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iMAG LTS Multi-Channel SQUID System

1. Figure 2 iMC 303 Multichannel SQUID Controller Rear Panel 2 5 System Interconnects 2 5 1 Composite Cable Connection The Composite Cable is used to transmit power and high speed control signals to the iFL 301 Flux Locked Loop and to transfer analog signals to the iMC 303 Multichannel SQUID Controller This cable contains a composite of shielded conductors and fiber optics Attach the 5 pin LEMO cable connectors to the iMC 303 Multichannel SQUID Controller Channel 1 2 or 3 mating LEMO connector on the rear panel and to the mating LEMO connector on the corresponding Flux Locked Loop To do this simply align the red dots on the mating connectors and push until it clicks in place To remove pull back on the knurled portion of the cable connector Do not twist the LEMO connector Remove the protective covers from the ends of the fiber optic cables labeled Clock and Data Insert the cables into the iMC 303 Multichannel SQUID Controller rear panel and iFL 301 Flux Locked Loop fiber optic connectors labeled Clock and Data Carefully thread the connectors to avoid cross threading then tighten snugly to assure that a good connection has been made Use caution when handling the fiber optic cables The ends have been highly polished and any surface abrasion or severe bending of the cables may cause an unrecoverable degradation in performance CAUTION USE CAUTION WHEN HANDLING AND ROUTING THE FI
2. Tristan Technologies Page 8 iMAG Multi Channel SQUID System 2 6 Mounting The iMC 303 Multichannel SQUID Controller 2 6 1 Bench mounting The iMC 303 Multichannel SQUID Controller comes supplied ready for bench use Rubber feet covers are supplied on the bottom of the instrument which can easily be removed The front of the instrument may be elevated by removing the rubber covers inserting a small straight blade screwdriver into the large gray tabs on the bottom cover and prying up Slide these tabs into the small gray feet and replace the rubber covers In order to stack more than one iMC 303 Multichannel SQUID Controller first remove the rubber feet covers and retract the large gray tabs into their original positions Then simply place one controller on top of the other and slide the feet into the alignment slots on the top of the instrument you wish to stack 2 6 2 Rack Mounting An optional rack mount kit for a standard 19 inch rack is available for the iMC 303 Multichannel SQUID Controller Tristan Technologies Page 9 MAG 303 Multi Channel SQUID System Chapter 3 Initial Power Up and Channel Installation 3 Initial Power Up and Channel Installation 3 1 Introduction Before applying power to the iMC 303 Multichannel SQUID Controller follow the INSTALLATION Procedure outlined in Chapter 2 of this manual Once the initial inspection of the system components has been completed and the system interconnects have been
3. QHPF SISTATE Format SISTATE lt 0 OFF 1 RUN 2 MANUAL TUNE 3 AUTOTUNE gt iMAG Response None Description Sets the system state of the iMAG When the system is in OFF mode voltage samples are not displayed on the front panel In RUN mode samples are displayed on the front panel and high speed data acquisition can be triggered In TUNE mode the user can perform a manual tune by adjusting the positive bias and modulation When set to AUTOTUNE the system automatically tunes the active channels and then displays the results on the front panel QTUNESTAT can be used to check the status of each channel as it is being tuned or to view the results after the tune is complete The default is 0 Related Commands QISTATE QTUNESTAT SHEAT Tristan Technologies Page 60 MAG 303 Multi Channel SQUID System SLEW Format SLEW lt Channel 1 3 gt lt 0 NORMAL 1 SLOW gt iMAG Response None Description Sets the system Slew value SLOW can only be used if the gain is set to x100 or higher The default is NORMAL Related Commands QSLEW SLLOCK Format SLLOCK lt 0 no lockout 1 local lockout gt iMAG Response Once the Local Lockout mode is set the front panel keyboard is disabled until the LOCAL key is pressed or SLLOCK 0 command is invoked from remote I O Description On the GPIB interface once the Local Lockout mode is set the front panel REM LED is lit and the fro
4. The iMAG enclosure measures 321mm wide 121mm high 300 mm deep 12 6 x 4 8 x 11 8 and weighs 6 3 kg 14 lbs It may be used either stand alone or incorporated in an instrument rack with an optional rack mount kit 8 5 Power 8 5 1 AC Power Requirements The instrument requires single phase AC power of 50 to 60 Hz Voltages are selectable at the power entry module for 100 120 220 240 VAC Tolerance on voltages is 10 8 5 2 Instrument Fusing A user replaceable fuse is mounted in the power entry module This module also includes a spare The fuse required is a 3A slow blow for 100 and 120 Vac and 1 5 A slow blow for 220 or 240 Vac Tristan Technologies Page 40 MAG 303 Multi Channel SQUID System 8 5 3 Power Grounding Requirements The Ground wire on the AC line cord must be connected to a safety ground that does not normally carry electrical current This safety ground becomes the Chassis Ground of the instrument and is used as the ground point for all cable shields Thus it is important to ensure a good quality connection Tristan Technologies Page 41 MAG 303 Multi Channel SQUID System Appendix A Remote Interface Commands Appendix A Remote Interface Commands Remote interface commands are used with a GPIB IEEE 488 or RS232 interface All commands are applicable to IEEE 488 but some are specific to IEEE 488 use The GPIB common commands and GPIB query commands described below cannot be used wi
5. 1 ON OFF N INSTALLED CHANNEL 2 ON OFF NOT INSTALLED CHANNEL 3 ON OFF NA AUXILIARY INPUT ON OFF NOT INSTALLED COMPOSITE DATA RATE IS 2 5kHz CHANNEL BIAS VOLTAGE OUT MODULATION CHANNEL 1 ON OFF LEVEL X X V CHANNEL 2 ON OFF LEVEL X X V CHANNEL 3 ON OFF LEVEL X X V CHANNEL MULTIPLIER EXPONENT 1 1 00 15 2 99 99 15 3 1 00 1 OFFSET AUX 1 0 INSTALLED CHANNELS 1 LTS 2 LTS HEATER ACTIVATION TIME 10 Sec WAIT TIME AFTER HEATER 30 Sec SUCCESSFUL TUNE VOLTAGE 2 00 Volt FLL MASTER CLOCK SETTING MASTER SLAVE AUTO INITIALIZATION ON OFF Figure 5 Menu Tree Page 15 MAG 303 Multi Channel SQUID System 4 8 OPERATING MODES AND MENU DESCRIPTIONS The iMC 303 Multichannel SQUID Controller has three distinct modes of operation the RUN SETUP and TUNE modes These are accessed using the buttons in the FUNCTION section of the front panel or via the remote interface If the iMC 303 Multichannel SQUID Controller is in the LOCAL condition REMOTE indicator LED turned off pressing any of these buttons will immediately place the iMAG into the indicated operating mode regardless of its current status 4 8 1 RUN RUN mode is entered by pressing the RUN button on the front panel The following screen will be displayed CHANNEL 1 HI PASS DC 3 1 69V LO PASS 5Hz GAIN x100 OFFSET 20 SLEW Normal CM Figure 6 Run Menu 4 8 1 1 CHANNEL Once the cursor has been moved to the CHANNEL position the disp
6. 41 Appendix A Remote Interface Commands iii 42 IEEE Command EE 46 a T EE 46 ELE E AT E 46 PR EE 46 e ET 46 WA A A EA 46 IEEE Query Command Reference aiii ad 48 VESES A A E ASA 48 INT A a 48 O NS EE 48 SR EE 49 ent NN EE 49 IMAC Commands EE 50 BH a Ge re EE DoT RL iE Sere 50 TINT es occ hice aa tia Fate aa ce te ol a dt oe am a NS 50 RE D NEE 50 CDC O al 50 EK et EE 51 TPC EE 51 COTE Sorts end abc Wana NAS te AN es Mee Ss eg 53 BEI E 53 DORE A EE 53 OSAMA 53 A a a a a E a aN 53 A an Ce antenne Ten ne 54 Tristan Technologies Page vi iMAG Multi Channel SQUID System QTBIAS N iii ta da tits 54 RRE 55 SUBA E 55 IM e a s 55 AE ha AS a E E E a DS 55 OTUNESTAT E A a eue 55 QUERREG ee 56 SADO EE 56 SAINT EE ee e 56 SARES EE 57 SARM airaa ida 57 GE 58 SDAPCK ee rsa Sn a ade ea 58 SDARM RE Sea ae hia at ct gu ope Na Sala en ed tat Palen oes 59 EE 59 SELEMCER A a 59 SGAN EE 60 SHEA Ti AA a Mra cece aoa 60 ei ias 60 SISTATE EE 60 Geer 61 EISEN 61 SELOCK anrasin ee ee eee a 61 O on so A Re ae eee tie eva ad anand nested cv aa Ca aan TH poe 61 SOFA a Aaa 61 SRATE pida 61 STBTASN A AA cue aeons 62 STBIAS AA 62 STMO D A ee 62 A ie ag a aah me ce 62 BK OS LAIN EE 62 SYSHEA EE 63 SYSVOL Lai A A 63 SYSWAI ias 63 SUERRE o oo tala nr tas 63 Appendix B Example E 64 E e dl e O 64 GPIB e 65 RS 232 Example PLO EE 66 GPIB Example PLO EC Ee ee EE e 67 Appendix C Application Notes on High Speed Data Acgut
7. Bandwidth Selections tin ee ie 38 Table 6 Summary of Remote Interface Commandes 43 Table 7 iFL 301 Pigtail Connector Pinout Face View 75 Tristan Technologies Page ix MAG 303 Multi Channel SQUID System Chapter 1 Introduction Congratulations You are now the owner of an iMAG Series SQUID System The iMAG Series is a family of advanced superconducting magnetic sensing components made by Tristan MAC products are designed to allow you to make use of the unique performance advantages inherent in superconducting quantum interference devices with a new generation of high performance sensors based on revolutionary high temperature superconductor technology The high temperature iMAG SQUID sensor provides magnetometer performance at 77 K that is commercially available nowhere else and that is competitive with any device reported in research laboratories Your high temperature or low temperature MAG System also includes high performance SQUID control electronics The iMC 303 Multichannel SQUID Controller is a microprocessor controlled instrument that provides advanced operation and control functions for up to three SQUID sensors and provides digital and analog outputs via standard interfaces The iMC 303 mates to a companion iFL 301 flux locked loop for each sensor channel via a copper and fiber optic interconnect The flux locked loop is an extremely compact module designed to be installed near the cryogenic sensor head multiple loops c
8. ESE ESR SRE SRE Tristan Technologies Page 49 MAG 303 Multi Channel SQUID System IMAG Commands Reference QADDR Format QADDR iMAG Response A three byte value indicating the GPIB address of the instrument Example QADDR 15 Description Inquire about the current IEEE 488 GPIB address setting for the instrument The number will be between 0 and 15 If the remote interface is set to RS232 the number 232 will be returned Related Commands SADDR QAINIT Format QAINTT iMAG Response A one byte value indicating automatic initialization selection 0 is OFF 1 is ON Example QAINIT 1 Description Inquire about the automatic initialization setting For an ON setting upon power on the iMAG controller will first check the installed channels and compare their respective triangle height against the GOOD TUNE VOLTAGE If any one of the installed channels is less than the GOOD TUNE VOLTAGE the system will do an AUTOTUNE for all installed channels If the system pass the AUTOTUNE it will proceed to the RUN screen Otherwise it will remained in the AUTOTUNE screen to show the AUTOTUNE results For an OFF setting upon power on the iMAG controller will proceed to the RUN screen without going through the auto initialization Related Commands SAINIT QARESET Format QARESET lt Channel 1 3 gt iMAG Response An 8 byte ASCII character string of 2 parameters each ended with a semicolon The firs
9. ESR SRE SRE STB RST Format RST iMAG Response None Description The Reset command resets the iMC 303 Multichannel SQUID Controller remotely This is equivalent of cycling the power on the iMC 303 Multichannel SQUID Controller Related Commands None SRE Format SRE lt register enable value gt iMAG Response None Description The Service Request Enable command sets the Service Request Enable Register as defined by the IEEE 488 2 1987 document Related Commands SRE WAI Format WA iMAG Response None Tristan Technologies Page 46 MAG 303 Multi Channel SQUID System Description The Wait to Continue command is a synchronization command It prevent the iMC 303 Multichannel SQUID Controller from executing any further commands or queries until there is no operation pending Since all iMC 303 Multichannel SQUID Controller commands are instantaneous executable commands this command is seen as a no operation command Related Commands OPC OPC Tristan Technologies Page 47 MAG 303 Multi Channel SQUID System IEEE Query Command Reference ESE Format ESE iMAG Response A 4 byte ASCII character string containing a value ranging from 0 to 255 Example ESE 255 Description The Standard Event Status Enable Query requests the Standard Event Status Enable Register content in the 1MC 303 Multichannel SQUID Controller The content of the register can be interpreted base
10. MAG 303 Multi Channel SQUID System User s Manual for IMAG LTS Multi Channel SQUID System f iMAG Multichannel SQUID Controller By Tristan Technologies www tristantech com San Diego California USA copyright 1993 1999 iMAG Multi Channel SQUID System TRISTAN TECHNOLOGIES Inc Part Number 3000 079 Revision Record 1999 by Tristan Technologies Inc All rights reserved No part of this manual may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording or otherwise without prior written permission of Tristan Technologies Inc Tristan Technologies Inc reserves the right to change the functions features or specifications of its products at any time without notice Any questions or comments in regard to this product and other products from Tristan please contact Tristan Technologies TRISTAN TECHNOLOGIES INC 6185 Cornerstone Court East STE106 San Diego CA 92121 U S A www tristantech com info tristantech com Technical Support 858 550 2700 Fax 858 550 2799 Page ii iMAG Multi Channel SQUID System WARRANTY Tristan Limited Warranty Tristan Technologies Inc warrants this product for a period of twelve 12 months from date of original shipment to the customer Any part found to be defective in material or workmanship during the warranty peri
11. using the INC or DEC keys iMAG supports RS 232 baud rates between 300 and 38 400 The Parity is set to None and Bits per Word as 8 and may not be changed by the user Once a selection has been made it will be entered into non volatile memory upon exit of the REMOTE I O menu 4 8 2 2 DIGITAL DATA ACQUISITION DIGITAL DATA ACQUISITION CHANNEL 1 ON CHANNEL 2 NOT INSTALLED CHANNEL 3 ON AUXILIARY INPUT OFF COMPOSITE DATA RATE IS 2 5 kHz Figure 10 Digital Data Acquisition Screen The DIGITAL DATA ACQUISITION screen displays the current status of data acquisition This is a status screen only data acquisition parameters may only be set over the IEEE 488 interface The channel status is ON OFF and NOT INSTALLED The data acquisition rate per channel is displayed on the lower portion of the display See Appendix A under SDACQ command and Appendix C High Speed Data Acquisition for details The iMC 303 Multichannel SQUID Controller is capable of Data Acquisition rates of 20 kHz for one channel Data Acquisition is limited to IEEE 488 interface only due to the inherent data transfer rate requirement The Data Acquisition rates are shown below for the different channel configurations Tristan Technologies Page 19 MAG 303 Multi Channel SQUID System Table 1 Data Acquisition Rates vs Channel Configuration 4 8 2 3 MANUAL TUNE The optimum SQUID TUNE parameters may be found manually via the MANUAL TUNE menu MANUAL TUNE C
12. Exponent value is displayed For the Auxiliary channel the display will use the result of MX B where M is the Multiplier and B is the OFFSET value This menu can be used for conversion of voltage to femtotesla or other units The range of Multiplier is between 99 99 to 99 99 The range of Exponent is between 15 to 15 4 8 2 6 CHANGE SYSTEM DEFAULT SYSTEM DEFAULT INSTALLED CHANNELS HEATER ACTIVATION TIME WAIT TIME AFTER HEATER SUCCESSFUL TUNE VOLTAGE Figure 14 System Default Menu Tristan Technologies Page 22 MAG 303 Multi Channel SQUID System 4 8 2 6 1 INSTALLED CHANNELS and CHANNEL CONFIGURATION The SYSTEM DEFAULT menu allows the user to set the basic operating parameters for each MAG channel To install a SQUID channel simply move the cursor to the Channel using the SELECT key and change the channel configuration from OFF to LTS or HTS The LTS selection is used for your Low Temperature SQUID system The operation of each channel requires the use of the correct iFL 301 Flux Locked Loop configuration iFL 301 L for your system The AUTOTUNE and AUTOTUNE after heat functions look at the configuration of each channel before performing the algorithms Any channels configured but not connected will still be HEATED and AUTOTUNED This will not damage the system or it s components but will slow the algorithms The AUXILIARY CHANNEL configuration menu selections are ON or OFF 4 8 2 6 2 HEATER The HEATER
13. HTS SQUIDs currently being fabricated Use the Vio value measured or that recorded in the System Integration Test report and scale accordingly Tristan Technologies Page 37 MAG 303 Multi Channel SQUID System 8 2 2 System Performance for SQUID with Open Input Coil The specifications below outline operation in the x1 x10 and x100 Gains for the LTS SQUID Sensor with open input coil The volts out may change by a small factor when an inductively matched load is attached to the input coil Gain Selection Input Current for Input Flux for Full Volts Out Amp In Volts Out p In Full Scale Output Scale Output 100 x 10 500 do 0 210x107 Table 4 System Performance for SQUID with Open Input Coil 8 2 3 System Noise Specification The equivalent input noise for the standard LTS SQUID system is less than 10x10 VHz from 1 Hz to 50 kHz in the 500 Range A Low noise version is available that has a SQUID with noise of less than 5x10 VHz from 1 Hz to 50 kHz in the 500 O Range 8 2 4 Bandwidth Selections There are two FLL operating bandwidths that are selected via the SLEW selection in the RUN menu See table below The response is flat from DC to the 3 dB points given below for the different selections fe 3dB 500 Hz 50 kHz Table 5 Bandwidth Selections 8 2 5 Slew Rate The Flux Locked Loop can track an input signal up to a maximum amplitude vs frequency before it flux jumps loos
14. Mounting 9 BIAS 20 C CHANGE SYSTEM DEFAULT MENU 23 CHANNEL 16 CHANNEL CONFIGURATION 23 Channel Installation 11 Clock Connections 8 Composite cable 35 Cursor Keys 13 D DATA ENTRY Keys 13 Determining the Voltage Flux Transfer Function V 30 DIGITAL DATA ACQUISITION 19 DIGITAL DATA ACQUISITION SCREEN 19 DISPLAY CONFIGURATION MENU 22 Tristan Technologies Page 76 E Enclosure 40 ENTER 13 Execution Error Register 46 56 64 F Fiber Optic Composite Cable 5 Flexible Cryogenic Cable 5 Front Panel 12 Function Keys 12 Fuse 6 41 G GAIN 17 Gain and Range Selections 37 GPIB 42 50 51 56 57 58 59 64 Grounding 6 H HEAT Key 14 HEATER 23 HEATER ACTIVATION TIME 23 Heater Status Screen 24 HIGH PASS FILTER 16 39 I IEEE Command Reference 46 IEEE Common Queries 42 IEEE Query Commands 48 IEEE Standard 488 1978 40 IEEE Standard Codes 42 TEEE 488 8 13 40 42 iFL 301 Flux Locked Loop 33 MAG Commands Reference 50 IMAG System Configuration 4 iMAG System Specifications 37 Initial Power Up and Channel Installation 10 Installation 5 INSTALLED CHANNELS 23 Tristan Technologies iMAG 303 Multi Channel SQUID System Page 77 K Keypad Summary 12 L Line Voltage 5 LOCAL 61 LOCAL Key 13 Low Noise Operation 32 LOW PASS FILTER 16 39 LTS Input Inductance 39 M Manual Tune 28 MANUAL TUNE MENU 20 MASTER 25 Mechanical Fo
15. a maximum 7 Ifthe TUNE levels just obtained are not within 20 of those on the Sensor Test Report it is possible that flux has been trapped in the SQUID Sensor Perform a heat cycle and manually retune the SQUID Remember that an AUTOTUNE will always be automatically executed after a heat cycle Tristan Technologies Page 28 iMAG 303 Multi Channel SQUID System 8 Once the TUNE parameters have been determined record them for future reference 5 1 3 Reset As discussed earlier the SQUID responds to applied flux in a periodic fashion Each periodic fluctuation is described as 1 Py or Flux Quantum Since the SQUID is sensitive to changes in magnetic flux there may be occasions when there is a relatively constant field which has caused the iMAG output to flux jump or lock on an operating point that is more than 1 Do from the zero field point For instance if a permanent magnet has been moved near the sensor This effectively decreases the dynamic range of the system Applying a RESET cancels the amount feedback current to the SQUID then resumes normal operation within 10 After a RESET the voltage out of the system is 0 the amount of voltage which corresponds to 1 for that GAIN setting set in the RUN display Tristan Technologies Page 29 MAG 303 Multi Channel SQUID System Chapter 6 Useful Operating Techniques 6 Useful Operating Techniques 6 1 Introduction This section of the manual describes some techniq
16. de power isolation and RFI filters e A Command decoder circuit executes commands transmitted from the MC 303 Multichannel SQUID Controller e A digital to analog converter circuit that generates levels for SQUID Bias and Modulation signals from SQUID to SQUID Preamplifier Bandpass Integrator Feedback Filter Range Select Figure 18 FLL Block Diagram 7 5 Control Unit Interface Connection to the iMC 303 Controller is via a five pin LEMO type connector and two fiber optic cables The bundle of five copper wires and two fiber optic links is assembled into a single 20 composite cable A single 5 pin LEMO circular connector is used to connect DC power to the iFL 301 from the iMC 303 Controller and Analog Output signals from the iFL 301 to the iMC 303 Controller e Analog Output consists of a shielded twisted pair e DC power is 8V 8V and ground e Two fiber optic cables are used to connect the 1 MHz clock and serial command data to the FL 301 Flux Locked Loop 7 6 Physical Description The iFL 301 contains a single electronic circuit board enclosed in a machined aluminum box It measures 3 5 x 3 5 x 0 6 and weighs 7 5 0z 210 grams The connection between the iFL 301 and the SQUID is made using an 18 pigtail wire assembly Tristan Technologies Page 35 MAG 303 Multi Channel SQUID System 7 7 Product Specifications iFL 301 L The Tristan Low Temperature Flux Locked Loop uses low noise DC biasing
17. in the iMAG command set This program can be used as a foundation on which more sophisticated programs can be built TEST3 C a better GPIB test program for the iMC 303 using National Instruments GPIB library include decl h DOS gpib header file include lt stdio h gt include lt string h gt void write_gpib char send void wait_loop long num void query_gpib char send char rcvd int HANDLE void main void char inbuf 80 int tuning HANDLE ibfind DEV15 connect to device el if HANDLE lt 0 printf error no connection established return ibeos HANDLE 0x140A EOS on linefeed ibtmo HANDLE 12 3 second timeout l write_gpib CLS reset buffers t wait_loop 6 query_gpib IDN inbuf get device id printf Connected to s n inbuf write_gpib SISTATE1 set to run mode Ei query_gpib QSAMP 1 inbuf read chl voltage F printf channel 1 reading s n inbuf write_gpib SYSCHAN2 1 enable channel 2 write_gpib SDPCHAN2 set display to ch2 vi query_gpib QSAMP 2 inbuf read ch2 voltage printf channel 2 reading s n inbuf query_gpib QHPF 1 inbuf query ch1 HP filter i printf channel 1 HP filter s n inbuf query_gpib QGAIN 2 inbuf query ch2 gain printf channel 2 gain s n inbuf printf now starting auto tune n write_gpib SISTATE3 tuning 1 while tuning sta
18. keys other than the LOCAL key are disabled if the REMOTE indicator LED is on Remote operation of the iMC 303 Multichannel SQUID Controller will return with the next command received on a remote interface 4 4 RESET Key This key resets the operating point of the SQUID sensors to an output level closest to 0 volts DC 4 5 HEAT Key Regardless of the menu displayed pressing the HEAT key heats the SQUID sensor on all installed channels for a user selected period of time and then finds new operating parameters using the AUTOTUNE algorithm Tristan Technologies Page 13 MAG 303 Multi Channel SQUID System 4 6 Special Key Assignments While in the MANUAL TUNE menu with the cursor in the channel field pressing the ENTER key will place the system in RUN mode while remaining in the MANUAL TUNE screen The user may then manually adjust the tune parameters while the system remains in RUN mode Tristan Technologies Page 14 4 7 Menu Tree SETUP SETUP SCREEN Remote UO Screen Digital Data Acquisition Screen Manual Tune Screen Reset Configuration Screen Display Configuration Screen Change System Default Values Screen Tristan Technologies MAG 303 Multi Channel SQUID System TUNE RUN RUN SCREEN AUTOTUNE VOLTAGE HI PASS Algorithm LO PASS GAIN Remote UO Selection OFFSET IEEE 488 Bus Address SLEW RS232 Baud Rate RS232 Parity RS232 Bits Per Word Bar Chart Display CHANNEL
19. parameters for each flux locked loop channel Setting Auto reset to ON will cause that channel to Auto tune each time the system is reset or the power is cycled The default is ON Related Commands QARESET SARM Format SARM iMAG Response Continuous stream of voltage samples from the iMC 303 Multichannel SQUID controller Description Triggers the high speed data acquisition mode When SARM is received the front panel indicates high speed data acquisition mode and a continuous stream of data is sent across the remote interface GPIB only until the SDARM command is received Before the SARM command is sent the user should set up the data acquisition parameters using SYSCHAN SRATE SDAPCK and SDACQ commands SYSCHAN is used to enable the SQUID channels SDACQ selects the channels to acquire data from and the composite rate SRATE and SDAPCK are used to change acquisition defaults Example SYSCHAN1 1 SDACQ 1 3 SARM The above example sets the instruments state to RUN mode sets channel for data collection with a data transfer rate of 20 000 words per second See Appendix C for further descriptions and examples Related Commands SDARM SRATE SDACQ QDACQ SDAPCK QDAPCK Tristan Technologies Page 57 MAG 303 Multi Channel SQUID System SDACQ Format SDACQ lt Channel select 1 11 gt lt Speed Select 0 3 gt us em SDACQ 4 lt 0 3 gt 4 AUX 0 15253 2 5K 5K 10K 20K SDACQ 6 lt 0 2 gt 0 1 2 2 5
20. 0 12 2 00 Description Inquires about the system default values Related Commands SYSCHAN SYSHEAT SYSVOLT SYSWAIT QTBIASN Format QTBIASN lt CHANNEL 1 3 gt iMAG Response A 5 byte ASCII character string containing a value between 0 and 100 Example QTBIASN 1 0 Description Inquires about the manual tune negative bias setting for the specified Flux Lock Loop channel The response is a percentage value Applies to Flux Lock Loop H configuration designed for use with HTS sensors Related Commands STBIASN Tristan Technologies Page 54 MAG 303 Multi Channel SQUID System QTBIASP Format QTBIASP lt CHANNEL 1 3 gt iMAG Response A 5 byte ASCII character string containing a value between 0 and 100 Example QTBIASP 1 57 Description Inquires about the manual tune positive bias setting for the specified Flux Lock Loop channel The response is a percentage value Related Commands STBIASP QTMOD Format QTMOD lt CHANNEL 1 3 gt iMAG Response A 5 byte ASCII character string containing a value between 0 and 100 Example QTMOD 1 29 Description Inquires about the manual tune Modulation setting for the specified Flux Lock Loop channel The response is a percentage value Related Commands STMOD QTSKEW Format QTSKEW lt CHANNEL 1 3 gt iMAG 1 Response A 5 byte ASCII character string containing a value between 0 and 100 Example QTSKEW 1 0 Description Inqui
21. 303 you will need a National Instruments IEEE 488 2 GPIB card or equivalent a GPIB cable and an IBM PC compatible with at least a 486 33 MHz processor or equivalent processing power IMAG and IEEE 488 commands In this document MAC commands will use the following font OM Are and IEEE 488 GPIB functions will use GPIB There are 8 data acquisition commands for the iMAG They are defined as follows SARM Triggers the flow of data from the MAG across the GPIB interface SDARM Halts the flow of data from the MAG SDACO Selects the channel s to sample and the data acquisition rate ODACO Query the MAG for the data acquisition parameters SDAPCK Set how often the SRQ line is set during high speed acquisition ODAPCK Queries how often the SRQ line is set during high speed acquisition SRATE Set up the format of the data packets for high speed data acquistion Some of the National Instruments GPIB functions that can also be used are IBFIND makes a GPIB connection IBTMO sets the timeout period for a read IBRD reads characters from the MAC IBWRT sends a command to the MAC IBRSP performs a serial poll Acquiring Data The first step in acquiring data is making sure you have a working GPIB connection between your PC and the iMC 303 Multichannel SQUID Controller Appendix B contains several test programs that may be helpful It should be noted that RS232 cannot be used for high speed acquisition Once your conne
22. 303 Multichannel SQUID Controller Operatpon 12 A Ne een EE EE 12 420 EEN 12 AR EE 12 422 DETUR REV er et as nn PR Net 12 425 EEN reegt 12 4 2 4 DATA ENTRY il las 13 ADS ELECTRA 13 4 2 6 INC increment and DEC decrement Keys 13 40 Teo E KR oeiseaseeo MeO 13 A3 LOCAL EE 13 A EE ba 13 4 5 HEAT E 13 4 6 Special e EE lathe durite ant 14 4T Mena rs tiia a A AA 15 4 8 OPERATING MODES AND MENU DESCRIPTIONS coooccnocccoccconicnninnono 16 A Sil ER eege 16 ARA CHANNEL e 16 Tristan Technologies Page iv iMAG Multi Channel SQUID System 4 8 1 2 HIGH PASS FILTER corrida lala stas 16 48 1 3 LOW PASS FILTER ot 16 EE e EE 17 E E 17 48 16 SLEW Eege EE eer 17 4 8 1 7 Output Voltage ee 17 AS BAC iS 17 4 8 1 9 Multi channel Barchart Dieplan 18 4827 EEN 18 482 de REMOTE VO tii 18 4 8 2 2 DIGITAL DATA ACQUISITION cocooccciccncconcnnninccnninnns 19 4 82 32 MANUAL TUNE le 20 A0 29 ET 20 4 8 2 3 2 MODULATION TEE 21 4 8 2 4 RESET CONFIGURATION cocoocccccccononncnnonncononnninccnninnos 21 4 8 2 5 DISPLAY CONFIGURATION 22 4 8 2 6 CHANGE SYSTEM DEFAULT ooooonconccccniccnoninncncnnonnos 22 4 8 2 6 1 INSTALLED CHANNELS and CHANNEL CONFIGURATION sassen 23 49 210 2 EE 23 4 8 2 6 3 SUCCESSFUL TUNE VOLTAGE issues 24 4 8 2 Te MISC MENU sidad tii 24 AS TUNE Sn A RS M os cn 25 5 Tuning and Operating the SQUID oi a seet deeg 27 SA AVOUE eessen een 27 5 1 1 Successful Tune E 28 Dole Manual KEE 28 DABS E EENE A E TEE 29 6
23. 5 continuous AUTORESETs may occur The range of the AUTORESET is 0 0 4 5 volts DC Channel overload hardware continuously monitors channels 1 3 signal levels before the High Pass Filter The outputs from each channel are wire ORed together If the signal on any channel exceeds 3 volts and any of the HIGH PASS Filters are engaged the Tristan Technologies Page 21 MAG 303 Multi Channel SQUID System microprocessor will be alerted If the AUTORESET is ON for any channel a RESET will be generated for all installed channels by the microprocessor The CHANNEL ON OFF field of the AUTORESET menu controls the RESET triggering from both the output voltage and channel overload conditions For either of the AUTORESET conditions to be triggerred the ON selection for the channel must be enabled 4 8 2 5 DISPLAY CONFIGURATION DISPLAY CONFIGURATION CHANNEL MULTIPLIER EXPONENT 1 1 00 0 2 1 25 15 3 1 00 0 1 00 3 Figure 13 Display Configuration Menu The DISPLAY CONFIGURATION menu allows the user to scale the display reading and unit The default settings for Multipliers and Exponents Offsets values are 1 00 and 0 respectively The front panel display will normally have a voltage value with a unit of V For channels 1 2 or 3 if the multiplier is other than 1 00 the multiplier will be applied to the voltage reading If the Exponent value is other than 0 the unit is V changed to read E for Exponent and the
24. AIT TIME AFTER HEATER 23 WARRANTY iii Tristan Technologies Page 80
25. BER OPTIC CABLES ANY SURFACE ABRASION OR SEVERE BENDING MAY CAUSE AN UNRECOVERABLE DEGRADATION IN PERFORMANCE Tristan Technologies Page 7 iMAG Multi Channel SQUID System 2 5 2 Cryogenic Cable Connection The Cryogenic Cable is the link between the SQUID Sensor immersed in a cryogen and the iFL 301 Flux Locked Loop at room temperature This is a flexible cable comprised of 5 shielded twisted pair transmission wires encased in a Teflon coated outer shield The inner and outer shields are constructed from 60 coverage braided phosphor bronze wire which provide excellent rejection of electro magnetic interference To connect the Cryogenic Cable to the iFL 301 align the red dot on the LEMO connector at the end of the iFL 301 Pigtail with the red dot on the connector at the mating end of the Cryogenic cable Push gently until it clicks in place To remove pull back on the knurled portion of the cable connector Do not twist the LEMO connectors To connect the Cryogenic Cable to the IMAG SQUID sensor align the red dot on the LEMO iMAG SQUID sensor connector with the mating end of the Cryogenic cable Push gently until it clicks in place To remove pull back on the knurled portion of the cable connector Do not twist the LEMO connectors 2 5 3 Remote Interface Connection Connection to the IEEE 488 is via an IEEE 488 connector on the rear panel Connection to the RS 232 is via a DB 9 connector on the rear panel The enabli
26. C increment and DEC decrement Keys The two keys labeled INC and DEC are used to scroll through the possible choices for a given item that has been selected using the SELECT Key For some fields like the BIAS and MODULATION selections in the MANUAL TUNE display it will increment or decrement numeric values for user selection Holding the INC and DEC keys will increment decrement the values more quickly These keys will also navigate through the selections in the SETUP menu 4 2 7 ENTER The ENTER key is used in the SETUP menu to choose which submenu to enter For instance to enter the MANUAL TUNE display press SETUP press SELECT or INC DEC until the cursor is on MANUAL TUNE then press ENTER The MANUAL TUNE display will appear on the front panel Pressing ENTER from the RUN screen will toggle between the RUN menu and the barchart view of the RUN menu Pressing ENTER from the Channel field of the MANUAL TUNE menu will transition the instrument to the RUN mode while remaining in the MANUAL TUNE menu This enables the user to adjust the TUNE parameters while the Flux Locked Loop is in the locked mode Pressing ENTER from any other menu has no effect on the state of the instrument 4 3 LOCAL Key Pressing the LOCAL key unconditionally terminates remote control of the iMC 303 Multichannel SQUID Controller via either the RS 232 or IEEE 488 port and turns off the REMOTE indicator LED This permits manual control via the front panel keys All
27. Function V A This is the relationship between the voltage output of iMAG input current at the SQUID Measuring this quantity requires injecting a known current into the input circuit of the SQUID and measuring the output voltage Again there is a potential for noise pickup in the leads connected to the input circuit so LC filtering may be necessary The setup is the same as that described in Section 6 3 The relationship of output voltage to current into the input coil of the SQUID is typically 5 0 x 10 in Gain x1 5 0 x 10 in Gain x10 5 0 x 10 V A in x100 Gain Tristan Technologies Page 31 MAG 303 Multi Channel SQUID System 6 5 Determining the Current Flux Transfer Function A The Current Flux transfer function is the amount of current flowing in the input coil which translates to 1 Do at the SQUID It may be calculated from the previous measurements from the test report or it may be measured by the following procedure 1 2 3 4 The same setup is used as described in Section 6 3 Observe the Voltage Flux Transfer Function V o on an oscilloscope If current is applied to the input coil a resultant flux will then be applied to the SQUID The V sinusoidal curve will move horizontally and each cycle corresponds to one flux quantum Do Place the peak of one cycle in the center of the oscilloscope by changing the input current or using the oscilloscope horizontal control Note the value of the input
28. HANNEL 1 BIAS 11 3 169V MODULATION 22 Figure 11 Manual Tune Menu The MANUAL TUNE menu allows the user to change the CHANNEL BIAS and MODULATION values Each of these values are displayed as a percent of full scale 0 100 The bar graph display and the large Voltage readout correspond to the peak RMS value of the SQUID Vid characteristic Full scale for these measurements is 0 4 5 volts DC Measuring the V characteristic is a quantifiable means of determining optimum SQUID TUNE parameters 4 8 2 3 1 BIAS The BIAS level is the actual amount of current applied to the SQUID sensor By increasing the amount of BIAS the current is increased across the superconducting Josephson junctions until a voltage is sensed by the iMC 303 Multichannel SQUID Controller This is the point called the critical current or I where the junctions can no longer support resistanceless current flow It is in a narrow region above the I that the optimum parameters for operating a SQUID are obtained Tristan Technologies Page 20 MAG 303 Multi Channel SQUID System BIAS can be adjusted from 0 100 The bar graph display and the Voltage readout on the screen will accurately show the SQUID s response to changes in the BIAS level 4 8 2 3 2 MODULATION MODULATION is the amount of current fed to a small discrete coil directly on top of the SQUID This current creates a small magnetic field which is sensed by the SQUID sensor and causes i
29. II character string containing a number from 1 to 4 Channels 1 to 3 are the Flux Locked loops and Channel 4 is the Auxiliary Analog input Example QDPCHAN 1 Description Inquire about the current controller display channel Related Commands SDPCHAN QDPMPL Format QDPMPL lt Channel 1 4 gt iMAG Response A 7 byte ASCII character string containing a value between 99 99 and 99 99 Example QDPMPL 1 1 00 Description Inquire about the multiplier value for a channel Related Commands SDPMPL QDPXO Format QDPXO lt Channel 1 4 gt iMAG Response A 4 byte ASCII character string containing a value between 99 99 and 99 99 Example QDPXO 1 0 Description Inquire about the exponent and offset value for a channel Tristan Technologies Page 51 MAG 303 Multi Channel SQUID System Related Commands SDPXO QFLLMCLK Format QFLLMCLK iMAG Response A 4 byte ASCII character string containing the value 1 or 0 1 indicates that the FLL master clock is set to Master 0 indicates Slave Example QFLLMCLK 1 Description Inquire about the FLL master clock setting Related Commands SFLLMCLK QISTATE Format QISTATE iMAG Response A 3 byte ASCII character string containing a value between 0 and 4 0 indicates that the instrument is in OFF mode 1 indicates RUN mode 2 indicates MANUAL TUNE mode 3 indicates that an AUTO TUNE is in progress and 4
30. K 5K 10K SDACQ 10 lt 0 1 gt 29 2 5K 5K SDACQ 11 lt 0 1 gt 3 AUX 2 5K 5K iMAG Response none Description Used to configure the high speed data acquisition parameters Parameter 1 selects the channel s to be sampled Parameter 2 selects the data acquisition rate for each individual channel Related Commands SARM SDARM QDACQ SRATE SDAPCK QDAPCK SDAPCK Format SDAPCK iMAG Response Sets the rate which determines how often the SRQ line is set during high speed data acquisition For instance a rate of 100 means the iMC 303 will output 100 packets of data and then set the SRQ line A packet contains 1 to 16 samples 2 32 bytes The default is 16 and can be changed using the SRATE command Example QDAPCK 100 Description Inquire about the current high speed data acquisition SRQ frequency Related Commands QDAPCK SARM SDARM SRATE SDACQ QDACQ Tristan Technologies Page 38 MAG 303 Multi Channel SQUID System SDARM Format SDARM iMAG Response none Description Halts high speed data acquisition When SDARM is received the front panel returns to run mode and the stream of data from the MAG is halted Related Commands SARM SDACQ QDACQ SRATE SDAPCK QDAPCK SDPCHAN Format SDPCHAN lt 1 4 gt iMAG Response None Description Sets the front panel display channel Channels 1 to 3 are the Flux Locked Loops 4 is the Auxiliary analog input channel The default displ
31. STBIASP lt CHANNEL 1 3 gt lt 0 100 gt iMAG Response None Description Sets the manual tune positive bias percentage level for the specified Flux Locked Loop channel value Applies to Flux Locked Loop H configuration designed for use with HTS sensors The default is 0 Related Commands QTBIASP STBIASN QTBIASN STMOD Format STMOD lt CHANNEL 1 3 gt lt 0 100 gt iMAG Response None Description Sets the manual tune modulation percentage level for the specified Flux Locked Loop channel The default is 0 Related Commands QTMOD STSKEW Format STSKEW lt CHANNEL 1 3 gt lt 0 100 gt iMAG Response None Description Sets the manual tune skew level percentage for the specified Flux Locked Loop channel value Applies to Flux Lock Loop H configuration designed for use with HTS sensors The default is 0 Related Commands QTSKEW SYSCHAN Format SYSCHAN lt Channel 1 3 gt lt for 1 3 O OFF 1 LTS 2 HTS for 4 Aux O OFF 1 ON gt iMAG Response None Description Configures the 4 system channels Channels 1 3 can be set to LTS HTS or Disabled Channel 4 aux can be set to ON or OFF The default is LTS for channel 1 OFF for the other channels Related Commands QSYSPARAM Tristan Technologies Page 62 MAG 303 Multi Channel SQUID System SYSHEAT Format SYSHEAT lt 1 50 Heater Activation Time gt iMAG Response None Description Sets the system heater a
32. The result of this biasing method is a clean FLL output spectrum that has a flat response to the specified bandwidth System Specifications 10 x 10 VHz Max from 1 Hz to 50 kHz in 500 range Full Scale Range 500 in GAIN selections of X1 X50 ee 5 in GAIN selections of X100 X500 Bandwidth 50 kHz in 500 range ee Selectable 50 kHz FAST or 500 Hz SLOW in 5 range Interface Modulation Drive Differential 500 kHz Square Wave Amplitude 0 to 50x 10 Amps Modulation Resolution One part in 256 Feedback Internal or external depending on internal jumper selection Differential DC Offset Flux Offset Resolution One part in 256 Interface Connector pin LEMO connector 8 VDC 8VDC Ground Analog Output Analog Return Analog Output Raw FLL output 3V Band limited to 50 kHz Output Impedance 500 Q FLL power requirement 175 mA at 8VDC Assumes SQUID input is connected to a 1800 nH load Table 2 FLL Specifications Tristan Technologies Page 36 MAG 303 Multi Channel SQUID System Chapter 8 Specifications 8 IMAG System Specifications 8 1 Introduction The iMAG DC SQUID System can be thought of as a very low noise current to voltage converter Since current flows in the SQUID input circuit in the presence of magnetic flux it can also be used as a flux to voltage converter It operates as a four terminal device with the current input leads at low temperature and the voltage output leads at r
33. Useful Operating LeCHMQUES tee EE eg 30 Gt OOo nr a tel ch re eas 30 6 2 Determining the Voltage Flux Transfer Function Ni 30 6 3 RE Interference and Shielding dass one sen dE nait 30 6 4 Determining the Voltage Current Transfer Function V A 31 6 5 Determining the Current Flux Transfer Function AO 32 6 6 Low Noise Op rations senisest ie E E ne 32 Ty APES OT Fl x Locked Loop EE 33 7 1 Background Infor ido 33 RE BE ENEE 33 1 3 IFL 301 L Wee 33 TA Funcional Descriptions en ne a 34 7 5 Control Unit Interface EE 35 0 Physical D s ription og oso nannan ae ald eee ta cee a atl ara 35 7 7 Product Specifications EE HE Eeer sed edd He 8 EE EE 37 8 1 Introduction EEN 37 EE ee 37 8 2 1 Gain and Range Selections venirse clio o arcada 37 8 2 2 System Performance for SQUID with Open Input Coil 38 Tristan Technologies Page v iMAG Multi Channel SQUID System 8 2 3 System Noise Specification iris tds 38 8 2 4 ee E TE EE 38 DD DIO Ee 38 ES A er Me A ds ue 39 E Output LS nn hued nie er St nn ne 39 82 8 KEEN 39 20 Low Pass EE 39 8 2 10 Auxiliary Analog put EE 39 E RR EE 40 A IN AAA A Ut dus 40 NA e EE 40 8 32 Remote Interfaces a ere dee Mela i Santee 40 8 3 1 LE Ee EE 40 8 3 2 RS 232 Eu EE 40 8 4 Mechanical Form Factors insu 40 E Mae ECOS de a EE PRE 40 DS PONT hee Ree 40 8 5 1 AC E Me ii 40 8 5 2 Instrument EE ee Eeer eng 40 8 5 3 Power Grounding Reoumrements
34. an be bolted together to minimize the space that they occupy This user s guide contains the information you need to install configure and operate the iMAG components that comprise the system you ordered It includes check out procedures and other useful information The iMAG Series is an innovative product that provides capabilities that in some cases have never been available before We at Tristan stand behind this product and are anxious to help you utilize it to its fullest potential Because iMAG is so new we ask that you take the time to study this user s guide in detail before attempting to use the system Once again thank you for becoming an iMAG customer Tristan Technologies Page 1 iMAG Multi Channel SQUID System 1 Introduction to the iMAG Multichannel System What is iMAG The 4 K System The basic LTS iMAG system essentially constitutes an extremely low noise ammeter that has zero input resistance The voltage output of the MAG system is proportional to current changes through the input terminals of the SQUID This ammeter has an input inductance of about 1800 nH negligible input capacitance and a frequency response that is flat from de to approximately 50 kHz A wide variety of input circuits can be connected to make different measurements Perhaps the most common input circuit is a simple pickup coil consisting of for example a single turn of niobium wire about one centimeter in diameter Such an input c
35. ange is automatically selected by changing the GAIN of the SQUID in the RUN mode The iMAG SQUID system operates in the 5009 range when GAINS of X1 X50 are selected and in the 59 range when GAIN is set to X100 X500 e Dual bandwidth in the 5 range 50kHz NORMAL and 500 Hz SLOW e DC Offset adjustment of 1 56 9 This adjustment is performed by driving de flux into the SQUID modulation coil e Two feedback modes Internal and external Selection made by internal jumper selection 7 4 Functional Description The Flux Locked Loop circuitry is a second order feedback loop plus required SQUID biasing circuitry see figure below It consists of the following e A SQUID signal preamplifier fabricated using a compound low noise JFET and op amp e A band pass filter which rejects the Modulation and frequency e A balanced demodulator circuit which is used to translate the SQUID signal to base band from its carrier frequency e A precision integrator plus a fixed pole filter which provides the desired second order loop response e The feedback drive circuit which drives the SQUID feedback coil e Peripheral FLL circuitry includes e A heater driver that provides DC power to the SQUID heater resistor This is activated from the control unit in order to drive the SQUID normal so that trapped flux may be purged Tristan Technologies Page 34 MAG 303 Multi Channel SQUID System e Local voltage regulators which provide
36. arity 4 A feedback circuit that uses the output of the phase sensitive detector to generate the feedback flux into the SQUID loop This circuit can be as simple as a resistor connected between the output of the phase sensitive detector and the modulation coil Typically an integrator circuit is used in addition to more accurately cancel the input flux FLUX LOCKED LOOP SUMMARY Feedback is used to keep the total flux constant in the SQUID Input signals are canceled by feedback and the feedback current is measured to determine the amplitude of the input signal 7 2 FL 301 L Configuration The version of the flux lock loop 1FL 301 L provided with your iMAG system has been specially designed for use with the Tristan LTS sensor 7 3 iFL 301 L Functions The iFL 301 Flux Locked Loop unit provides the following functions e Biasing of the SQUID DC Bias technique employed Tristan Technologies Page 33 MAG 303 Multi Channel SQUID System e Remote adjustment of BIAS and MODULATION levels are available from the iMC 303 Multichannel Control unit e Solid State heater a circuit available to purge trapped magnetic flux from the SQUID e Dual Range feedback loop Full scale ranges of 59 and 500 are selected by the user In the 50 the system provides the greatest sensitivity and the lowest noise sensor limited noise In the 500 range the system provides the greatest dynamic range electronics limited noise The r
37. auses the iMC 303 Multichannel SQUID Controller to enter the AUTOTUNE mode and determine the optimum SQUID TUNE parameters for each installed channel Once the TUNE key has been pressed the iMC 303 Multichannel SQUID Controller will display the AUTOTUNE screen and perform the AUTOTUNE sequentially for each installed channel TUNING will be displayed for all installed channels and the cursor will flash in the field of the channel currently being tuned AUTOTUNE CHANNEL 1 Tuning CHANNEL 2 Not Installed CHANNEL 3 Not Installed T_T rr rr Figure 17 Autotune Screen AUTOTUNE looks at the configuration HTS or LTS of the installed channels executes the appropriate AUTOTUNE algorithm to determine the optimum TUNE parameters Once the AUTOTUNE parameters have been determined they are saved in non volatile memory and are used to operate the SQUID sensor each time the RUN mode is entered The AUTOTUNE algorithm uses the SUCCESSFUL TUNE VOLTAGE in the CHANGE SYSTEM DEFAULT screen to determine whether the TUNE values resulting from the autotune are optimum This SUCCESSFUL TUNE VOLTAGE is the peak RMS magnitude of the periodic V signal observed at the Analog Output on the rear panel while in the MANUAL TUNE screen If the TUNE voltage for all installed channels is greater than the SUCCESSFUL TUNE VOLTAGE the system will automatically enter the RUN screen after completion of the AUTOTUNE If the TUNE voltage for any of the installed cha
38. ay channel is 1 Related Commands QDPCHAN SFLLMCLK Format SFLLMCLK lt 0 Slave 1 Master gt iMAG Response None Description Sets the FLL master clock setting 0 sets the FLL master clock to Slave 1 sets it to Master The default is 1 This is to link multiple iMAG controllers Related Commands QFLLMCLK Tristan Technologies Page 59 MAG 303 Multi Channel SQUID System SGAIN Format SGAIN lt Channel 1 4 gt lt 1 x1 2 x2 3 x5 4 x10 5 x20 6 x50 7 x100 8 x200 9 x500 gt iMAG Response None Description Sets the Gain value for the specified channel Parameters 1 9 are valid for channels 1 3 parameters 1 6 are valid for channel 4 auxiliary The default gain for each channel is x1 Related Commands QGAIN SHEAT Format SHEAT iMAG Response None Description Activates the system SQUID heater When SHEAT is received the front panel will indicate that the system heater is active The system will go into a heat cycle followed by a cool down period The command SYSHEAT is used to set the heater activation time and SYSWAIT sets the time for the cool down period An auto tune follows the cool down period Related Commands SYSHEAT SYSWAIT SYSVOLT QISTATE QSYSPARAM QTUNESTAT SHPF Format SHPF lt Channel 1 4 gt lt 0 DC 1 0 3Hz gt iMAG Response None Description Sets the High Pass Filter value for specified channel The default is DC Related Commands
39. cific operating environment 5 1 2 Manual Tune The optimum SQUID TUNE parameters are best found by using the AUTOTUNE algorithm Because the TUNE parameters may vary with the type of circuit connected to the SQUID Input Circuit or type of measurements being taken or even the level of electromagnetic noise present in the environmental setting the user may choose to set these parameters manually The TUNE parameters may be set manually by entering the MANUAL TUNE menu The MANUAL TUNE menu is obtained pressing the SETUP key on the front panel from any menu Select the MANUAL TUNE option by using the SELECT and ENTER keys MANUAL TUNE Procedure 1 Connect an oscilloscope to the Analog Output BNC of the appropriate channel on the rear panel Set the oscilloscope for DC coupling 2 0 volts div vertical scale and 1 msec div horizontal scale 2 Set the BIAS level to 0 and the MODULATION level to the value indicated in the Sensor Test Report It is possible that a new MODULATION value may be determined during the MANUAL TUNE procedure but this is generally the best starting point 3 Increment the BIAS level until the maximum signal peak is located Peak is the maximum voltage in a 20 window 4 Reduce the MODULATION to 0 then increment it until the maximum signal peak is seen on the oscilloscope 5 Again sweep the BIAS from 0 until the maximum peak signal is found 6 Readjust the MODULATION until the output on the oscilloscope reaches
40. correct value to prevent shock and fire hazards as well as damage to the MC 303 Mulitchannel SQUID Controller 2 2 2 Grounding The Ground wire on the AC line cord must be connected to a safety ground that does not normally carry electrical current This safety ground becomes the Chassis Ground of the instrument and is used as the ground point for all cable shields Thus it is important to ensure a good quality connection The iMC 303 Multichannel SQUID Controller comes equipped with a three conductor power cord that connects the instrument chassis to earth ground WARNING TO PREVENT SHOCK AND FIRE HAZARDS ALWAYS CONNECT THE POWER CORD TO A THREE CONDUCTOR GROUNDED RECEPTACLE 2 3 Operating Environment 2 3 1 Operating Temperature Range The iMC 303 Multichannel SQUID Controller is designed to operate over an ambient temperature range of 25 C 5 C 2 3 2 Humidity Altitude A normal laboratory environment is expected Proper operation over extremes of altitude or humidity is not guaranteed WARNING To prevent shock and fire hazards as well as damage to the iMC 303 Mulitchannel SQUID Controller it should not be allowed to get wet or operate in a condensing atmosphere Tristan Technologies Page 6 iMAG Multi Channel SQUID System 2 4 Rear Panel Layout The rear panel layout of the iMC 303 Multichannel SQUID Controller is illustrated in the following diagram 00000 0000
41. ction is established the next step is to enable the SQUID channels you want to acquire from SYSCHAN is used to enable the appropriate channels Next set the iMC 303 s data acquisition parameters SDACO allows you to select the channel or channels that will be sampled and also select the data acquisition rate If one of the channels you specify is not enabled the SDACQ command will not be accepted See Appendix A for valid configurations To trigger the flow of data use the SARM command When SARM is received the iMC 303 front panel display will indicate that a high speed transfer is in progress and data will be sent across the GPIB interface IBRD or IBRDA can be used to read the data into a character buffer IBTMO should be used to set the time out limit for IBRD If the time out period is too short IBRD will terminate before it has acquired all of the Tristan Technologies Page 71 MAG 303 Multi Channel SQUID System bytes you requested The size of the buffer can be as large as your computer will allow up to 1 gigabyte If you need to acquire data over a long period of time you can read smaller buffers in a loop See the Synchronization section below When you have acquired all the data desired issue the SDARM command to stop the flow of data Since there is a small lag time between sending the SDARM command and the time that the flow of data actually stops there may be a few bytes of data remaining in the iMC 303 s output bu
42. ctivation time constant from 1 to 50 seconds The default is 10 Related Commands QSYSPARAM SYSVOLT Format SYSTVOLT lt 0 4 5 Tune Voltage gt iMAG Response None Description Sets the system successful tune voltage value The default is 2 0 Related Commands QSYSPARAM SYSWAIT Format SYSWAIT lt 1 50 Wait After Heater gt iMAG Response None Description Sets the system wait time after heater activation The default is 12 Related Commands QSYSPARAM SUERREG Format SUERREG lt 1 Command Error Register 2 Execution Error Register gt lt Register value decimal gt iMAG Response None Description Sets the User Error Register enable bits The register value is converted from decimal to binary and the appropriate register bits are set User Error registers are internal iMAG registers The bits are normally set to zero If an error condition occurs and the enable bit for that condition is set the specific GPIB Standard Event Status Register bits are set accordingly bit 5 of ESR for command bit 4 of ESR for Execution Command Error Register Bit Definition Bit7 Bit6 BitS Bit4 Bit3 Bit 2 Bit 1 Bit 0 Not Not Not Not Not Bad Parameter Unterminated Unknown Used Used Used Used Used Command Command Execution Error Register Bit Definition Bit 7 Bit6 BitS Bit4 Bit3 Bit2 Bit 1 Bit 0 Not Not Not Transmit Buffer Parity Unknown GPIB Receive Buffer Transmit Buffer Used Used Used Overflow Error Error O
43. current Slowly increase the input current and count the peaks of the flux quanta as they pass the center of the screen The amount of current needed to move that number of flux quanta is the Current Flux Transfer Function A q Use at least 10 flux quanta to obtain an accurate measure of this relationship This reading is a set quantity and is independent of Gain setting on the iMAG controller 6 6 Low Noise Operation The following recommendations should be followed for operation in the lowest noise configuration 1 2 Unplug the fan by removing the connector from JP10 on the iMAG Controller PC board This will get rid of 220Hz and it s harmonics Operate with OFFSET at 100 to reduce low frequency noise Tristan Technologies Page 32 MAG 303 Multi Channel SQUID System CHAPTER 7 1F1 301 Flux Locked Loop 7 iF 1 301 Flux Locked Loop iFL 301 Flux Locked Loops are used in conjunction with LTS SQUID sensors provided with the iMAG Series of SQUID components These units operate under the control of the iMC 303 Multichannel SQUID Control The following discussion provides background and technical information about the iFL 301 7 1 Background Information The periodic outputs that are characteristic of the response of DC SQUIDs to external magnetic fields are not useful for practical applications Generally speaking a well behaved detector has an output that is linearly proportional to the input signal not periodic To ma
44. d on the IEEE 488 2 1987 document Related Commands CLS ESE ESR SRE SRE STB SUERREG QUERREG IDN Format IDN iMAG Response A 36 byte ASCII character string containing the device identification in the following format Tristan Model iMAG revision number Example IDN CONDUCT Model iMAG Rev 1 04 Description The Identification Query requests device identification The intent is to determine the unique identification of devices on the bus Related Commands RST OPC Format OPC iMAG Response A 2 byte ASCII character string containing the value 1 Example OPC 1 Description The Operation Complete Query returns a 1 when all pending operations are completed Related Commands OPC ESE ESE ESR SRE SRE STB Tristan Technologies Page 48 MAG 303 Multi Channel SQUID System SRE Format SRE iMAG Response A one byte value ranging from 0 to 63 or 128 to 191 Example SRE 255 Description The Service Request Enable query requests the Service Request Enable Register content The contents are defined by the IEEE 488 2 1987 document Related Commands SRE STB Format STB iMAG Response A one byte value ranging from 0 to 63 or 128 to 191 Example STB 115 Description The Read Status Byte query requests the Status Byte Register contents The contents are defined by the IEEE 488 2 1987 document Related Commands CLS
45. ecorded on the test report If the SQUID is sensing a signal which is greater than its bandwidth limit the output will appear small and distorted It is possible for the output not to appear at all if the interfering signal has an amplitude of Do 2 By placing the SQUID in a small shield the source of the interference may easily be determined 1 The following additional suggestions refer to the use of the LTS SQUID sensor 2 Ifthe transfer function indicates that interference is a problem the input circuit should be removed The SQUID can operate with an open or shorted circuit at this point Re check the transfer function to verify SQUID performance and a clean signal 3 Check the shielding around the entire input circuit Some environments contain huge amounts of RF interference and the shielding in this case must be excellent The optimum shield is of the superconducting variety which will also provide extra magnetic shielding 4 Ifthe shielding is not properly grounded to the system this may hinder the effectiveness of the shield 5 The input circuit must be entirely floating Any ground connected to the input causes the Voltage Flux Transfer Function to appear distorted 6 High impedance sources connected to the input circuit can degrade the transfer function so that it looks much the same as interference Best performance is achieved with a matching input impedance of 1800 x 10 H 6 4 Determining the Voltage Current Transfer
46. el 1 channel 3 channel 1 channel 3 Synchronization IBRD allows reading a buffer of up to 1 gigabyte provided the computer has that much available memory If the computer does not have sufficient space to store all the data you wish to acquire the computer can acquire smaller buffers in a loop and process the data in between reads When acquiring data in a loop over a long period of time it is advisable to use synchronization to ensure the integrity of the data To achieve synchronization the iMC 303 Controller asserts the SRQ service request periodically By default the SRQ line is always asserted once after 100 packets are sent The SDAPCK command can be used to change how often the SRQ line is set The frequency of the SRQ can be set from once after each packet to once after Tristan Technologies Page 72 MAG 303 Multi Channel SQUID System every 400 packets This allows you to use a serial poll to test for the SRQ line and then read a buffer of data when the line is asserted The following C code fragment shows a typical coding scheme using SRQ ibwrt handle SRE 255 9 enable status register ibwrt handle SDACQ1 0 9 channel 1 2500 KHz ibwrt handle SDAPCK100 10 set SRQ freq to 100 ibwrt handle SARM 5 start data flow count 0 while count lt bytes while bytes to acquire is less than the count statbyte 0 while statbyte amp 0x40 serial poll device un
47. en slowly reappear as the Sensor cools If the SQUID output signal does not completely disappear increase the HEATER ACTIVATION TIME until the SQUID output signal observed with the oscilloscope reaches zero Volts during a HEAT cycle If AUTOTUNE Tristan Technologies Page 27 MAG 303 Multi Channel SQUID System continues to fail after the HEAT cycle has been activated and confirmed to operate properly the TUNE parameters should be adjusted manually using the MANUAL TUNE menu It should be verified that the maximum RMS output signal observed at the Analog Output BNC on the rear panel is larger than the default SUCCESSFUL TUNE VOLTAGE value The SUCCESSFUL TUNE VOLTAGE value is displayed in the SYSTEM DEFAULT VALUES screen selectable from the SETUP menu The SQUID may still operate if the TUNE parameters cannot be adjusted manually to reach the default SUCCESSFUL TUNE VOLTAGE value but this can be a symptom of flux trapping excessive rf interference or inadequate shielding For further information see Section 8 4 on RF INTERFERENCE and SHIELDING or contact Tristan 5 1 1 Successful Tune Voltage The AUTOTUNE algorithm uses certain benchmarks to determine whether the TUNE values determined during the AUTOTUNE sequence are optimum One of these parameters is the SUCCESSFUL TUNE VOLTAGE This is the maximum RMS voltage of the SQUID voltage flux V output signal resulting from the AUTOTUNE This setting should be set by the user for his her spe
48. es its ability to track the input signal and locks on a different operating point for the SQUID The following figure shows typical vaues for the maximum input in bo peak for a sinusoid input vs Frequency that the Flux Locked Loop can track Tristan Technologies Page 38 MAG 303 Multi Channel SQUID System Slew Rate 10000 1000 100 Input phio 0 1 1 10 100 1000 10000 100000 Frequency Hz Figure 19 Slew Rate D vs Frequency Typical 8 2 6 SQUID Input The input inductance of the LTS SQUID is 1 8 x 10 H Connections are provided via two superconducting screw terminals for connection of an input coil 8 2 7 Analog Output The Analog Output BNC for each channel is found on the instrument back panel It is a pseudo differential type with an impedance of 500Q and full scale output of 4 5 volts 8 2 8 High Pass Filter The High pass is a single pole filter on the input circuit and is selected OFF for DC couple of 0 3Hz for a cut off frequency of 0 3 Hz 8 2 9 Low Pass Filter The low pass filter on the output circuit is a 4 pole Butterworth with selectable cut off frequencies of 5 Hz 500 Hz 5 kHz and Off When Off is selected the MAG system will have a maximum bandwidth of 50 kHz 8 2 10 Auxiliary Analog Input An auxiliary analog input is provided via BNC on the back panel This will allow a user provided signal to be digitized along with the SQUID signal This input will have the same signal condition
49. f x100 x500 Only the NORMAL selection is available when using the GAIN settings of x1 x50 The SLEW is set by default to NORMAL When selecting an SLEW setting the user should configure the instrument to track the signals from the SQUID Sensor Rf transients may cause the Feedback Loop to be unable to track the desired signal The NORMAL mode is generally less susceptible to rf transients and the SLOW mode is less effected by magnetic transients 4 8 1 7 Output Voltage The large characters in the display directly below the CHANNEL field display the SQUID Output Voltage This voltage corresponds to the amount of magnetic flux at the SQUID sensor V o The voltage is a function of the GAIN setting the higher the GAIN the higher the resultant output voltage The Output Voltage display is a digital representation of the level on the Analog Output BNC found on the rear panel The range for this output is 4 5 volts 4 8 1 8 Barchart The barchart at the bottom of the RUN screen is a graphical representation of the Output Voltage field and has a range of to 4 5 Volts Tristan Technologies Page 17 MAG 303 Multi Channel SQUID System 4 8 1 9 Multi channel Barchart Display When the cursor is in the CHANNEL field of the RUN menu pressing ENTER results in a multi channel display This multi channel display shows the numerical value of the selected channel and a graphical representation of the value of all 4 channels in barchart fo
50. ffer Use CLS to clear out the buffer Data Format In high speed data acquisition mode the iMC 303 Multichannel SQUID Controller sends out 2 byte ADC integer values from the selected channels To scale convert the 2 byte ADC integer value to a floating point voltage sample multiply by 4 5 32768 0 The following C routine shows how to convert a sample of binary data using an IBM PC void char_to_float char cval float fval union f num char cval 2 short ival fnum fnum cval 0 cval 1 fnum cval 1 cval 0 fval fnum ival 4 5 32768 0 Since the data is sent as individual bytes it must be pieced back together into meaningful data In the above routine a union is used to combine two individual character bytes into a single 2 byte short integer Notice that the two bytes must be swapped Finally the short is converted to floating point The 2 byte samples are sent across the remote interface in packets By default there are 16 samples 32 bytes in each packet The SRATE command sets the number of samples in each packet An SRATE value of 1 16 will set the number of samples in each packet to 1 16 respectively It should be noted that setting the SRATE to less than 16 will reduce the composite rate of transfer since fewer samples are being sent If more than one channel is selected the samples will be interleaved For example if you are sampling channels 1 and 3 the stream of data will look like this chann
51. gram ibconf GPIB Primary Address Secondary GPIB Address Terminate Read on EOS System Controller Assert REN when SC Enable Auto Serial Polling Enable CIC Protocol Bus Timing Cable Length for High Speed Parallel Poll Duration Use GPIB interface Base I O Address Interrupt Level DMA channel DMA Transfer Mode The following table illustrates the GPIB configuration dev15 accessed by executing the program National Instruments program ibconf In this case the iMC 303 Multichannel SQUID Controller is configured with GPIB address 15 which is the default address Primary GPIB Address Secondary GPIB Address Timeout setting Serial Poll Timeout Terminate Read on EOS Set EOI with EOS on Writes EOS byte Send EOI at end of Write Enable Repeat Addressing Tristan Technologies Page 65 MAG 303 Multi Channel SQUID System RS 232 Example Program The following is a sample C language DOS program written for the iMC 303 Controller TESTI1 C is a simple test program which verifies the communications link between the iMC 303 Controller and the host computer TEST 1 c A simple RS232 test program for the iMC 303 using National Instruments RS232 library define COMI 1 include rs232 h include lt stdio h gt include lt string h gt char inbuf 80 int i void main void OpenComConfig COM1 9600 0 8 1 80 80 0 0 initialize com1 ComWrt COM1 IDN 6 send co
52. her IEEE 488 or RS 232 interface ports and both are provided as standard features Full computer control of all front panel functions is provided e High Speed Data Acquisition The iMC 303 Multichannel SQUID Controller provides high speed data collection acquisition for all SQUID channels via the IEEE 488 interface port Configurable data acquisition rates up to 20 000 words per second are supported e Master Slave Configuration Multiple iMC 303 Multichannel SQUID Controller units can be configured to operate systems consisting of more than 3 SQUID sensors A clock input and output are provided on each unit so that a master clock can be used to drive all Flux Locked Loops in the system Tristan Technologies Page 3 iMAG Multi Channel SQUID System 1 1 MAG System Configuration iMC 303 SQUID CONTROLLER COMPOSITE CABLE iFL 301 FLUX LOCKED LOOP iFL 301 PIGTAIL CRYOGENIC CABLE SQUID SENSOR Figure 1 iMAG System Configuration Tristan Technologies Page 4 MAG 303 Multi Channel SQUID System Chapter 2 Installation and Setup 2 Installation and Setup 2 1 Unpacking And Inspection Prior to unpacking the iMAG system you should check the carton for any shipping damage If damage is observed notify the carrier immediately to allow for a possible insurance claim The following items are included with the standard iMAG system If any items are missing notify your Tristan
53. ichannel SQUID Controller will display Tuning and perform the AUTOTUNE sequence described above for each installed channel If the TUNE voltage detected is greater than the default SUCCESSFUL TUNE VOLTAGE setting the RUN mode will be automatically entered If the TUNE voltage detected is less than the DEFAULT setting the MANUAL TUNE mode will automatically be entered It is not necessary to perform an AUTOTUNE each time the power is removed from the iMC 303 Controller Once the AUTOTUNE parameters have been determined they are saved in non volatile memory and are used to operate the SQUID Sensor each time the RUN key is pressed or on power up The AUTOTUNE should be repeated under the following conditions 1 Tune voltage is significantly lower than previously known good values 2 SQUID will not lock 3 Range changed between 3 o and 500 Do GAINS of 1x 50x and 100x 500x The system will most likely perform adequately without retuning but for optimum performance but retuning may be necessary 4 A large field or transient has caused the SQUID to loose lock and rail the output signal Connect an oscilloscope to the Analog Output for the appropriate channel on the rear panel to observe the sinusoidal SQUID V f output signal Press the HEAT key on the front panel and verify that the output signal decreases to zero before the HEATER ON message displayed by the iMAG Controller turns off The sinusoidal SQUID output signal should th
54. indicates that the SQUID heater is activated Example QISTATE 1 Description Inquire about the current state of the instrument Related Commands SISTATE SHEAT QGAIN Format QGAIN lt Channel 1 4 gt iMAG Response One of the following 5 byte ASCII character strings x1 x2 x53 x10 x20 x50 x100 x200 x500 Example QGAIN 1 x1 Description Inquire about the GAIN value for the specified channel Related Commands SGAIN Tristan Technologies Page 52 MAG 303 Multi Channel SQUID System QHPF Format QHPF Channel 1 4 gt iMAG Response One of the following 7 byte ASCII character strings DC or 0 3Hz Example QHPF 1 DC Description Inquire about the High Pass Filter value setting for the specified channel Related Commands SHPF QLPF Format QLPF lt Channel 1 4 gt iMAG Response One of the following 7 byte ASCII character strings OFF 500Hz 5kHz SHz Example QLPF 1 OFF Description Inquire about the Low Pass Filter value setting for the specified channel Related Commands SLPF QOFFSET Format QOFFSET lt Channel 1 3 gt iMAG Response A 5 byte ASCII character string containing a value between 100 and 100 Example QOFFSET 1 1 Description Inquire about the OFFSET setting for the specified channel Related Commands SOFFSET QSAMP F
55. ing and filtering options as the SQUID channels Tristan Technologies Page 39 MAG 303 Multi Channel SQUID System 8 2 11 A D converter A two channel 16 bit 20 kHz Analog to Digital converter handles the A D conversion of the 3 SQUID channels as well as the AUX Analog Input channel 8 2 12 User Interface The user interface to the control unit is via a ten button keypad and an eight line by 40 character LCD display Menus allow easy access to all available functions 8 2 13 Front Panel The Front Panel is a membrane type with a ten key keypad and an LCD display of 40 characters on each of 8 lines An LED on the panel indicates that the controller is in remote mode the controller is currently being accessed by the IEEE 488 or RS 232 ports and the keypad is locked out 8 3 Remote Interfaces IEEE 488 and RS 232 interfaces are both standard All functions and read outs available from the instrument may be completely controlled by either interface via remote computer 8 3 1 IEEE 488 Interface The IEEE 488 interface allows complete remote control of the instrument as well as the ability to read all information to full internal accuracy The interface is compliant with IEEE Standard 488 1978 8 3 2 RS 232 Interface The RS 232 interface allows full operation of the instrument as does the IEEE 488 interface The Baud rate is selected by the front panel Maximum Baud rate is 38 400 8 4 Mechanical Form Factors 8 4 1 Enclosure
56. itialized channel TEST4 C get a buffer of data using high speed data acquisition and National Instruments GPIB library include decl h DOS gpib header file include lt stdio h gt include lt string h gt void write_gpib char send void wait_loop long num int HANDLE void main void char inbuf 1000 HANDLE ibfind DEV15 connect to iMAG ibtmo HANDLE 12 set timeout to 3 sec ibeos HANDLE 0x0 turn off EOS write_gpib SDACQ1 3 channel 1 20 KHz write_gpib SARM trigger data flow wait_loop 10 ibrd HANDLE inbuf 1000 read 1000 bytes printf read d bytes from iMAG ml ibent write_gpib SDARM stop data flow S write_gpib CLS clear MAC out buffer 24 See Appendix C for more information on high speed data acquisition Tristan Technologies Page 70 MAG 303 Multi Channel SQUID System Appendix C High Speed Data Acquisition Notes Appendix C Application Notes on High Speed Data Acquisition The iMC 303 Multichannel SQUID Controller is designed to make high speed data acquisition simple and reliable Data may be acquired at a composite rate of up to 20 000 samples per second via the IEEE 488 bus and you can sample 1 2 or 4 channels simultaneously There is no limit to the number of samples you can acquire For large acquisitions a synchronization signal is provided to ensure integrity To acquire voltage samples from the iMC
57. ke the output linear a flux locked loop is employed This circuit applies a feedback flux to the loop to cancel any signal flux Since the feedback signal is exactly equal to the input signal one needs only to measure the feedback to know how much the flux changed at the input A generic flux locked loop comprises 1 A modulation circuit that applies a small ac usually square wave flux to the SQUID loop It has a peak to peak amplitude of 1 2 Dy and a typical frequency of 500 kHz This circuit comprises a simple fixed frequency and fixed amplitude oscillator whose output is connected to a coil the modulation coil that couples this flux into the SQUID loop 2 A phase sensitive detector This circuit uses the modulation signal as a reference and measures the amplitude and phase of the signal coming from the SQUID that is due to the modulation flux It comprises a simple phase sensitive detector connected to the fundamental SQUID output described above 3 For those who are unfamiliar with phase sensitive detectors they require two inputs a reference input and a signal input to produce one output The output voltage is proportional to the ac amplitude of input signals whose frequency and phase are the same as that of the reference signal Other ac input signals with a few notable exceptions especially at harmonics create no output If the input signal is 180 degrees out of phase with the reference signal the output voltage reverses pol
58. layed channel can be scrolled using the INC and DEC keys The operating parameters may be changed for each installed channel If the displayed channel has not been installed Channel Disabled will appear on the screen Note that when changing the AUX CHANNEL settings in the RUN display the SLEW and OFFSET are disabled These are SQUID Sensor parameters and are not available with the AUX CHANNEL 4 8 1 2 HIGH PASS FILTER The HIGH PASS FILTER is a single pole filter that is applied to the input signal from the SQUID sensor prior to amplification This filter resides in the MC 303 Multichannel SQUID Controller It can be set for DC no filtering or 0 3 Hz equivalent to the AC coupling feature found on some instruments which has a corner frequency of 0 3 Hz 4 8 1 3 LOW PASS FILTER Each channel may be filtered by choosing one of three four pole Butterworth filters The LOW PASS FILTER settings are OFF 5 Hz 500 Hz and 5 kHz By selecting OFF the Analog Output bandwidth is limited by the FL 301 Flux Locked Loop to 50 kHz Tristan Technologies Page 16 MAG 303 Multi Channel SQUID System 4 8 1 4 GAIN The GAIN setting represents the gain applied to the signal prior to the LOW PASS FILTER and the Analog Output This voltage output is a direct conversion of the flux in the SQUID sensor For instance a gain of x5 will yield 5 times the voltage measured at the Analog Output as a gain of x1 will for the same amount of applied f
59. ler can be configured to support a multi channel SQUID system consisting of more than the 3 channels supported by each iMC 303 Multichannel SQUID Controller The rear panel CLOCK Input and Output BNCs provide a mechanism for all of the iFL 301 Flux Locked Loops to be driven by a Master Clock One iMC 303 Multichannel SQUID Controller is designated the MASTER and it s CLOCK Output is connected to subsequent controllers CLOCK Input These iMC 303 Multichannel SQUID Controllers are designated SLAVE If only one iMC 303 Multichannel SQUID Controller is used it must be designated MASTER Tristan Technologies Page 24 MAG 303 Multi Channel SQUID System If AUTO INITIALIZATION is set to ON each installed Flux Locked Loop channel will be checked for its RMS value against the SUCCESSFUL TUNE VOLTAGE upon power up If the level is lower than the SUCCESSFUL TUNE VOLTAGE the system will automatically perform an AUTOTUNE all channels If any one of the installed channels does not pass the check the system will automatically enter the MANUAL TUNE menu If all passed it will automatically enter the RUN menu If AUTO INITIALIZATION is set to OFF the iMC 303 Multichannel SQUID Controller will enter the RUN menu on power up 4 8 3 TUNE The easiest method for finding the optimum SQUID operating parameters is to take advantage of the MAC AUTOTUNE algorithm Regardless of the menu currently displayed pressing the TUNE key c
60. lux at the SQUID sensor There are nine possible GAIN selections in this menu x1 x2 x5 x10 x20 x50 x100 x200 and x500 The overall gain is a combination of gains in the iMC 303 Multichannel SQUID Controller out of loop gain and in the iFL 301 Flux Locked Loop in loop gain For GAIN selections x1 x2 x5 x10 x20 and x50 the in loop gain is unity For GAIN selections x100 x200 and x500 the in loop gain is set at x100 The range of the Feedback Loop also changes as a function of the selected GAIN The output can track 500 D 1000 Po peak to peak in x1 x2 x5 x10 x20 x50 selections and 5 Do 10 Do peak to peak in the x100 x200 and x500 GAIN selections 4 8 1 5 OFFSET The OFFSET feature allows the user to inject a DC offset current into the Modulation coil to effectively null the DC output of the SQUID sensor This gives the iMC 303 Multichannel SQUID Controller maximum dynamic range and allows the gain setting to be increased to obtain maximum sensitivity The OFFSET range on the display is 100 100 This corresponds to 1 5 Do at the SQUID in the 500 Dj range and is independent of the GAIN setting Low frequency noise will be injected by settings other than 100 4 8 1 6 SLEW RATE There are two SLEW selections operating bandwidths NORMAL 50KHz and SLOW 500Hz which allow the user to optimize feedback loop performance using the SQUID Sensor Both NORMAL and SLOW are available when using the GAIN settings o
61. made the SQUID sensor is ready to cool in liquid Helium 3 2 Connecting to the Tristan LTS SQUID Sensor The LTS Sensors are shipped with a superconducting short across the input terminals To make a connection with the input circuit of the sensor loosen the 0 80 brass screws Place the interconnect wires in contact with the Niobium terminals on the SQUID circuit board and tighten the screws It is important that this connection is of high quality especially if the input circuit must be superconducting 3 3 Cooling the Tristan SQUID Sensor IMAG SQUID sensors are mounted in a rigid assembly which provides mechanical support and protection for the SQUID The assembly also shields the sensor from certain levels of electro magnetic interference Cool the SQUID as slowly as is practical Slow cooling ensures that a minimal amount of thermal stress will occur and reduces the chances of any ambient field becoming trapped in the SQUID The sensor is shielded but some levels of high and low frequency electromagnetic interference can cause trapped flux especially if an inductive input circuit is connected to the SQUID This can significantly degrade the performance of the system and additional shielding may be required 3 4 Initial Power Up Sequence And Display When the iMC 303 Multichannel SQUID Controller is first powered up it goes through a series of internal tests The results of these tests is displayed on the Self Test screen show
62. mmand for 1 0 1 lt 10000 14 i i i delay loop ComRd COM1 inbuf 35 read response K inbuf strlen inbuf 0 null terminate string printf Connected to s n inbuf end of TEST1 C Tristan Technologies Page 66 MAG 303 Multi Channel SQUID System GPIB Example Programs The following are sample C language DOS programs written for the iMC 303 Controller TEST2 C is a simple program which verifies the communications link between the iMC 303 Controller and the host computer TEST2 c A simple GPIB test program for the iMC 303 using National Instruments GPIB library include decl h DOS GPIB header file include lt stdio h gt include lt string h gt int handle char inbuf 80 int i void main void handle ibfind DEV 15 connect to device if handle lt 0 printf error no connection established return ibtmo handle 11 set timeout to 1 seconds ibwrt handle IDN 6 query device ident for 1 0 1 lt 10000 14 1 1 i delay loop ibrd handle inbuf 80 read response inbuf strlen inbuf 0 null terminate string printf Connected to s n inbuf end of TEST2 C Tristan Technologies Page 67 MAG 303 Multi Channel SQUID System TEST3 C is a model program that verifies the communications link between the iMC 303 Controller and the host computer through a series of basic commands found
63. n in figure 15 The ROM checksum and revision are also displayed here Tristan Technologies Page 10 MAG 303 Multi Channel SQUID System SELF TEST IN PROGRESS CPU MC68331 PASS RAM 64K B PASS Non Volatile RAM PASS ROM Checksum 2200 PASS Remote I O PASS ispLSIRPC 1 Tristan Model MAC Rev 2 00 Figure 3 Self Test Screen After the self test is complete the MC 303 Multichannel SQUID Controller defaults into the RUN mode and the screen will change to the RUN display This process normally takes about 2 seconds The iMC 303 Multichannel SQUID Controller will use the TUNE values stored in memory to operate the SQUID sensor 3 5 Channel Installation and Using iMAG The correct SQUID sensor and channel information should be verified in the SYSTEM DEFAULT menu prior to operating the iMC 303 Multichannel SQUID Controller with a SQUID sensor The operation of each SQUID channel also requires the use of the correct iFL 301 Flux Locked Loop configuration To perform the channel configuration 1 Press the SETUP key to display the SETUP menu 2 Press the SELECT key to move the cursor to CHANGE SYSTEM DEFAULT 3 Press the ENTER key 4 Press the SELECT key to move the cursor to the channel you wish to install 5 Use the INC or DEC key to change the channel configuration to match the iFL 301 Flux Locked Loop and SQUID sensor connected to the rear panel The AUTOTUNE and HEATER functions poll the configuration of each channel bef
64. ng of the desired interface is done via menu selection on the front panel 2 5 4 Auxiliary Channel Connections The auxiliary input is provided for signal conditioning and digitizing of a user supplied signal This input has the same signal conditioning options as the 3 SQUID channels The user may monitor this channel via the analog output on the back panel or the remote interfaces 2 5 5 Clock Connections The CLOCK Input and Output BNC s make it possible for several MC 303 Multichannel SQUID Controllers to be interconnected for operation of systems consisting of more than three SQUIDs In this configuration one iMC 303 Multichannel SQUID Controller is designated MASTER via menu selection and its CLOCK Output is connected to subsequent controllers CLOCK Input The clock signal is then daisy chained from CLOCK Output to CLOCK Input of remaining Controllers These remaining iMC 303 Multichannel SQUID Controllers are designated SLAVE via menu selection In this manner the MASTER iMC 303 Multichannel SQUID Controller provides a common clock for all iFL 301 Flux Locked Loops Use of this common clock eliminates the need for multiple clocks to drive the SQUIDs ensuring that harmonics are not generated in multiple SQUID configurations Each iMC 303 Multichannel SQUID Controller is then controlled individually through the front panel or computer interface to change operating parameters and acquire data
65. nnel SQUID System Table 6 Summary of Remote Interface Commands Common IEEE Commands Name Description ESE Event Status Enable OPC Operation Complete RST Reset Command Tristan Technologies Page 43 MAG 303 Multi Channel SQUID System QLPF Query low pass filter value for channels 1 4 QSLEW Query slew rate value for channels 1 3 sus Tristan Technologies Page 44 MAG 303 Multi Channel SQUID System ES Tristan Technologies Page 45 MAG 303 Multi Channel SQUID System IEEE Command Reference CLS Format CLS iMAG Response None Description The Clear Status command clears the Standard Event Status Register s bit 4 and bit 5 Execution Error bit and Command Error bit and the content of Execution Error Register and Command Error Register This command also resets the input and output character buffers Related Commands ESE ESE ESR SRE SRE STB SUERREG QUERREG ESE ESE Format ESE iMAG Response None Description The Event Status Enable command sets the Standard Event Status Enable Register bits as defined by the IEEE 488 2 1987 standard Related Commands CLS ESE ESR SRE SRE STB SUERREG QUERREG OPC Format OPC iMAG Response None Description The Operation Complete command sets the Standard Event Status Register s bit 0 Operation Complete bit when all the pending operations are completed Related Commands OPC ESE ESE
66. nnels is less than the SUCCESSFUL TUNE VOLTAGE the system will automatically enter the Tristan Technologies Page 25 MAG 303 Multi Channel SQUID System MANUAL TUNE screen with channel 1 selected whether it is installed or not The SQUID may still operate but this may indicate flux trapping excessive RF interference or inadequate shielding Tristan Technologies Page 26 MAG 303 Multi Channel SQUID System Chapter 5 Tuning and Operating the SQUID 5 Tuning and Operating the SQUID 5 1 Autotune The best method to find the optimum SQUID operating parameters is to take advantage of the iMAG AUTOTUNE algorithm Regardless of the menu currently displayed pressing the TUNE key causes the iMC 303 Multichannel SQUID Controller to execute the AUTOTUNE algorithm and determine the optimum SQUID tune parameters for each installed channel The AUTOTUNE algorithm sequence is described below 1 Tune parameters are set to BIAS 0 MODULATION 15 or last current value if gt 10 2 BIAS is swept from 0 100 The corresponding to peak voltage is stored and BIAS set to that level Peak is the maximum voltage in a 20 window 3 MODULATION is swept from 0 100 The corresponding to peak voltage is stored and MODULATION set to that level 4 BIAS is again swept from 0 100 The corresponding to peak voltage are stored and BIAS set to that level 5 The AUTOTUNE is complete Once the TUNE key has been pressed the iMC 303 Mult
67. nt panel keyboard is disabled until the LOCAL key is pressed or SLLOCK 0 command is invoked from the remote I O For RS232 interface the REM LED is not changed The front panel keyboard is disabled when SLLOCK 1 command is invoked Related Commands QLLOCK SLPF Format SLPF lt Channel 1 4 gt lt 0 OFF 1 500 Hz 2 5000 Hz 3 5 Hz gt iMAG Response None Description Sets the Low Pass Filter for the specified channel The default is OFF Related Commands QLPF SOFFSET Format SOFFSET lt Channel 1 3 gt lt 100 to 100 gt iMAG Response None Description Sets the OFFSET percentage value for the specified channel Value must be a value within the range of 100 to 100 Volts The default is 0 Related Commands QOFFSET SRATE Format SRATE lt 1 16 gt iMAG Response None Description Sets the format of the data packets in high speed data acquisition A packet can contain 1 to 16 samples 2 32 bytes The default is 16 Setting SRATE to a value less than 16 will lower the overall composite acquisition rate Tristan Technologies Page 61 MAG 303 Multi Channel SQUID System Related Commands QTBIASP STBIASN QTBIASN STBIASN Format STBIASN lt CHANNEL 1 3 gt lt 0 100 gt iMAG Response None Description Sets the manual tune negative bias percentage level for the specified Flux Locked Loop channel The default is 0 Related Commands QTBIASN STBIASP QTBIASP STBIASP Format
68. od will be repaired or replaced without charge to the owner Prior to returning the instrument for repair authorization must be obtained from Tristan Technologies Inc or an authorized Tristan service agent All repairs will be warranted for only the unexpired portion of the original warranty plus the time between receipt of the instrument at Tristan and its return to the owner This warranty is limited to Tristan s products that are purchased directly from Tristan its OEM suppliers or its authorized sales representatives It does not apply to damage caused by accident misuse fire flood or acts of God or from failure to properly install operate or maintain the product in accordance with the printed instructions provided This warranty is in lieu of any other warranties expressed or implied including merchantability or fitness for purpose which are expressly excluded The owner agrees that Tristan s liability with respect to this product shall be as set forth in this warranty and incidental or consequential damages are expressly excluded SAFETY PRECAUTIONS The instrument chassis must be connected to an electrical ground The three contact power cord supplied with the instrument provides a connection the power source and a protective ground The protective ground contact is connected to the instrument chassis Use a power source outlet which has a properly grounded protective ground contact to minimize a shock hazard Do remo
69. oil would be able to measure magnetic fields with a resolution of better than 10 femtotesla By forming more complex pickup coils such as gradiometer coils it is possible to improve the rejection of distant noise sources with little loss in signal sensitivity For example gradiometer coil configurations are used in biomagnetic measurements to reject environmental noise they are also used in laboratory measurements to reduce the background signal caused by magnet drift or temperature changes SQUIDs are also commonly used as the null detector in a bridge circuit The output signal from the SQUID is nulled by balancing a bridge circuit connected to the input of the SQUID One can determine small voltages or impedances using this method in the same way one uses a conventional bridge circuit Control Electronics Description The iMAG system is based upon a high performance multichannel controller designed for use with SQUID Superconducting Quantum Interference Device sensors The system has a wide range of features which allow high sensitivity and low noise operation Flexible channel configurations make it possible to control SQUID sensors operating at 77K or 4 K The iMAG System standard features include e Three Configurable SQUID Channels The iMC 303 Multichannel SQUID Controller allows simultaneous control of up to 3 SQUID channels Each channel may be independently configured for operation with 77 or 4 Kelvin SQUID sensors e Compact Remo
70. oom temperature with the transfer functions being very linear The RMS input noise is guaranteed to be less than 10 x 10 Hz LTS SQUID for frequencies greater than 1 Hz In this expression is the flux quantum where D 2 07 x 10 Weber or 2 07 x 10 Gauss cm The input inductance of the LTS SQUID Sensor is 1800 x 10 H The best performance will be achieved for load impedances of 500 2000 x 10 H If operation with a larger source impedance is desired performance may be improved by placing a low resistance shunt at the SQUID input terminals The extreme sensitivity of the DC SQUID Sensor requires care in the design of the input circuit especially with regard to grounding and shielding The general rule is to have the input circuit floating and well shielded to minimize rf interference Improper shielding will significantly degrade noise performance and slew rate 8 2 System Specifications 8 2 1 Gain and Range Selections Nine different Gain selections may be selected via the front panel in the RUN menu or by remote interface The selections are 1 2 5 10 20 50 100 200 and 500 The figure below shows the V and ranges for the available gain selections HTS SQUID sensor specifications may vary so for actual sensor performance specifications please refer to the SQUID Sensor or System Integration Test Report for your system Table 3 Gain vs Range the values in this table assume a V go value typical of
71. ore performing these functions Channels configured but not connected will still be HEATED and AUTOTUNED This will not damage the system or its components but does slow the process The iMAG System should now be ready for basic use Although the HEATER ACTIVATION TIME WAIT TIME AFTER HEATER and SUCCESSFUL TUNE VOLTAGE have all been preset at the factory these parameters may require some adjustment due to the type of application level of shielding or amount of electromagnetic interference in the environment Tristan Technologies Page 11 MAG 303 Multi Channel SQUID System Chapter 4 MC 303 Multichannel SQUID Controller Operation 4 iMC 303 Multichannel SQUID Controller Operation 4 1 Keypad Summary The response of the iMC 303 Multichannel SQUID Controller to its various keys is summarized in the following sections The FUNCTION keys change the iMC 303 Multichannel SQUID Controller operating Mode and the menu displayed on the screen The DATA ENTRY keys change the settings within each menu The LOCAL key allows access to the front panel keys while the unit is interfaced with a remote computer Once a setting has been changed it is stored in non volatile memory When the instrument power is cycled the most recent setup and operating parameters are retained TRISTAN mMm S TECHNOLOGIES DATA ENTRY NC SELECT DEC ENTER iMAG Multichannel SQUID Controller Fig
72. ormat QSAMP lt Channel 1 4 gt iMAG Response A 12 byte ASCII character string containing a value between 4 5V to 4 5V or the 17 byte message Channel disabled Example QSAMP 1 1 350V Inquire about the current sensor voltage for the specified channel Related Commands SARM STEST SDARM SDACO QDACQ QSLEW Format QSLEW lt Channel 1 3 gt iMAG Response One of the following 7 byte ASCII character strings SLOW NORMAL Example QSLEW 1 NORMAL Tristan Technologies Page 53 MAG 303 Multi Channel SQUID System Description Inquire about the slew setting for the specified channel Related Commands SLEW QSYSPARAM Format QSYSPARAM iMAG Response A 32 byte ASCII character string of seven parameters each ended with an semicolon The first three strings are either OFF LTS or HTS denoting whether the respective channel is configured for LTS low temperature sensor HTS high temperature sensor or not installed The fourth string is either YES or NOT indicating whether or not the auxiliary channel is installed The fifth string is a value between 1 and 50 and it denotes the system heater activation time in seconds The sixth string is a value between 1 and 50 and denotes system wait time after the heater activation The seventh string is a value between 4 5 and 4 5 and it denotes the successful tune voltage Example QSYSPARAM LTS HTS OFF YES 1
73. provides a 16 volt source which is used to raise the temperature of the SQUID Sensor above its superconducting transition temperature inorder to purge any magnetic flux trapped in the sensor Trapped flux can cause the SQUID Sensor to operate with less than optimal parameters The heater current passes through a small resistor mounted close to the SQUID chip in the sensor package The HEATER ACTIVATION TIME is the amount of time maximum of 50 seconds that voltage is applied to each of the installed SQUID Sensor heater resistors Because of the many applications for SQUID sensors and the conditions in which they are used the amount of time required to heat the SQUID varies with the application The WAIT TIME AFTER HEATER is the amount of time maximum of 50 seconds that allows the SQUID Sensor to adequately cool below its superconducting transition temperature before an AUTOTUNE is performed to optimize the SQUID parameters To determine the appropriate HEAT and WAIT times perform the following procedure 1 Enter the MANUAL TUNE menu 2 Monitor the Analog Output BNC of the channel of interest with an oscilloscope 3 Press the HEAT key on the iMC 303 Multichannel SQUID Controller front panel The V response signal on the oscilloscope should decrease when heated until the magnitude of the signal drops to 0 volts DC Notice the display on the iMC 303 Multichannel SQUID Controller It should still be counting down the HEATER ON
74. r Parity Unknown GPIB Receive Buffer Transmit Buffer Used Used Used Overflow Error Error Overflow Under flow Related Commands SUERREG SADDR Format SADDR lt 0 15 or 232 gt iMAG Response None Description Set the IEEE GPIB address for the instrument This number must be between 0 to 15 The system default is 15 For an RS232 interface SADDR 232 will do the initial switch from IEEE to RS232 Related Commands QADDR SAINIT Format SAINIT lt 1 ON 0 OFF gt iMAG Response None Example SAINIT 0 Description Sets the automatic initialization setting For an ON setting upon power on the iMAG controller will first check the installed channels and compare their respective triangle height against the GOOD TUNE VOLTAGE If any one of the installed channels is less than the GOOD TUNE VOLTAGE the system will do an AUTOTUNE for all installed channels If the system pass the AUTOTUNE it will proceed to the RUN screen Otherwise it will remained in the AUTOTUNE screen to show the AUTOTUNE results For an OFF setting upon power on the iMAG controller will proceed to the RUN screen without going through the auto initialization Manufactory default sets it to ON Related Commands QAINIT Tristan Technologies Page 56 MAG 303 Multi Channel SQUID System SARESET Format SARESET lt Channel 1 3 gt lt 0 OFF 1 ON gt lt Reset voltage 4 5 to 4 5 gt iMAG Response None Description Sets the Auto reset
75. representative immediately 2 1 1 Packing List e 1 iMC 303 Multichannel SQUID Controller Configured for your line voltage e to 3 iFL 301 Flux Locked Loop Module s e 1 to 3 SQUID Sensor s e to 3 Flexible Cryogenic Cable s e 1 to 3 Fiber Optic Composite Cable s 6 1 meters each e to 3 System Integration Test Report s e 1 to 3 SQUID Test Report s e one LTS iMAG Multi Channel SQUID System User s Manual e AC Power Cord 2 2 Power Requirements All system power is supplied to the SQUID Controller The iMC 303 Multichannel SQUID Controller is configured to support ac voltages of 100 120 220 240 Volts at either 50 or 60 Hz These voltage selections are enabled by rotating the jumper block in the fuse drawer on the back of the unit to display the desired operating voltage in the window Tolerance on voltages is 10 WARNING Never attempt to operate the iMC 303 Multichannel SQUID Controller at a different input line voltage than is shown on the power input module on the rear panel Serious injury or damage may result Tristan Technologies Page 5 iMAG Multi Channel SQUID System 2 2 1 Instrument Fusing A user replaceable fuse is mounted in the AC power entry module This module also includes a spare The iMC 303 Multichannel SQUID Controller requires a 3 Amp slow blow fuse for 110 and 120 VAC configurations and a 1 5 Amp slow blow fuse for 220 and 240 VAC configurations WARNING Always replace the fuse with the
76. res about the Manual Tune SKEW percentage value Applies to Flux Lock Loop H configuration designed for use with HTS sensors Related Commands STSKEW QTUNESTAT Format QTUNESTAT iMAG 1 Response A 9 byte ASCII character string containing 3 parameters each ended with a semicolon Each of the three parameters represents the AUTO TUNE status of one of the three flux lock loop channels The value 0 indicates that the channel auto tuned successfully The value 1 indicates that the channel failed to auto tune The value 2 indicates that the channel is currently being auto tuned and 3 indicates that the channel is not installed Example QTUNESTAT 1 3 3 Description Inquires about the AUTO TUNE status of the 3 flux lock loop channels Tristan Technologies Page 55 MAG 303 Multi Channel SQUID System Related Commands QISTATE SISTATE SYSVOLT QUERREG Format QUERREG lt 1 Command Error Register 2 Execution Error Register gt iMAG Response One ASCII byte indicating the register contents in decimal Example QUERREG 1 5 Description Queries the User Error registers This command will also clears the register content Command Error Register Bit Definition Not Not Not Not Not Used Bad Parameter Unterminated Unknown Used Used Used Used Command Command Execution Error Register Bit Definition Bit 8 Bit7 Bit6 Bits Bit4 Bit3 Bit 2 Bit 1 Not Not Not Transmit Buffe
77. rm The full scale corresponds to 4 5V to 4 5V CHANNEL 1 3 169V Figure 7 Multi channel Barchart Screen 4 8 2 SETUP The SETUP menu allows the user to enter the appropriate menu to manually change any of the desired operating parameters of the iMC 303 Multichannel SQUID Controller The selections under the SETUP menu are REMOTE I O DIGITAL DATA ACQUISITION MANUAL TUNE RESET CONFIGURATION DISPLAY CONFIGURATION CHANGE SYSTEM DEFAULT and MISC The SELECT key and the INC and DEC keys are used to navigate through the selections The ENTER key brings up the menu for the selection highlighted by the cursor SETUP REMOTE UO DIGITAL DATA ACQUISITION MANUAL TUNE RESET CONFIGURATION DISPLAY CONFIGURATION CHANGE SYSTEM DEFAULT MISC Figure 8 Setup Menu 4 8 2 1 REMOTE I O Select the REMOTE I O menu from the SETUP Menu to change the remote I O configuration Details on Remote commands are described in Appendix A Tristan Technologies Page 18 MAG 303 Multi Channel SQUID System REMOTE I O Remote I O Selection RS232 IEEE 488 Bus Address 15 RS232 Baud Rate 38400 RS232 Parity OFF RS232 Bits Per Word 8 Figure 9 Remote I O Menu The iMAG comes configured with IEEE 488 as the default setting Use the SELECT and the INC or DEC keys to change the setting Please note that only one of the interface connections can be activated at a time Enter any desired IEEE 488 address between 1 31 inclusive
78. rm Factors 40 MENU DESCRIPTIONS 16 Menu Tree 15 MISC MENU 25 MODULATION 21 O OFFSET 17 Operating Environment 6 OPERATING MODES 16 Output Voltage 17 18 P Packing List 5 Power Grounding Requirements 41 Power Requirements 5 R Rack Mounting 9 Rear Panel 7 Receive Buffer Overflow 56 64 Remote Control 13 40 REMOTE I O 19 REMOTE I O MENU 19 Tristan Technologies iMAG 303 Multi Channel SQUID System Page 78 iMAG 303 Multi Channel SQUID System Remote Interface Connection 8 RESET CONFIGURATION 21 RESET CONFIGURATION MENU 21 RESET Key 13 Revision Record ii RF Interference and Shielding 30 RS 232 8 13 40 RUN 11 RUN KEY 12 RUN Menu 16 S SAFETY PRECAUTIONS iii SELECT Key 13 Self Test Screen 11 Setup 5 SETUP Key 12 SETUP MENU 12 18 SLAVE 25 SLEW RATE 17 38 Special Key Assignments 14 SQUID Interface Connector Pinout 75 SQUID Reset 29 SQUID Sensor Connection 10 SQUID Sensor Cooling 10 Standard Event Status Register 46 64 SUCCESSFUL TUNE VOLTAGE 24 System Interconnects 7 System Noise Specification 38 System Performance for SQUID with Open Input Coil 38 T Technical Support ii The iMAG System 2 Transmit Buffer Overflow 56 64 TUNE 25 Tuning and Operating the SQUID 27 Tristan Technologies Page 79 MAG 303 Multi Channel SQUID System U Unpacking 5 Useful Operating Techniques 30 User Error Register 64 W W
79. rt auto tune printf query_gpib QISTATE inbuf loop until done if stremp 3 inbuf 0 tuning 0 wait_loop 12 Tristan Technologies Page 68 MAG 303 Multi Channel SQUID System query _gpib QTUNESTAT inbuf get tune results printf nresults of auto tune s n inbuf end main a routine to send a command to the iMC 303 void write _gpib char send ibwrt HANDLE send strlen send ay if ibsta amp 0x8000 check for GPIB error printf GPIB error d on ibwrt n iberr end write_gpib a delay loop void wait_loop long num long 1 j 0 for 1 0 i lt num 10000 i j 2 j end wait_loop a routine to send a query to the iMC 303 and read the response void query_gpib char send char recv char buffer 80 write_gpib send send command wait_loop 5 wait for response ibrd HANDLE buffer 80 read response RI if ibsta amp 0x8000 check for GPIB error printf GPIB error d on ibrd n iberr return buffer ibent 1 0 null terminate string strepy recv buffer end query gpib Tristan Technologies Page 69 MAG 303 Multi Channel SQUID System TEST4 C is a test program that verifies the Data Acquisition function of the iMC 303 Controller The Data Acquisition is initialized and assigned a 1000 byte buffer then the iMC 303 acquires 1000 bytes of data from each in
80. spon 71 IMAG and IEEE 488 commands di ii 71 PC GUAT EE 71 Data Format EE 12 A O A ed 72 Appendix D SQUID Interface Connector Pinout ooonoccnccccnoncconccconaconnnonn conc ccnnncnonocinnos 75 Tristan Technologies Page vii iMAG Multi Channel SQUID System Tristan Technologies Page viii MAG Multi Channel SQUID System Table of Figures Figure 1 1MAG System Configurations cin a di Ana cees malins 4 Figure 2 iMC 303 Multichannel SQUID Controller Rear Panel 7 Piste 3 Self A a E a E E e EEN E A mene 11 Figure 4 iMC 303 Multichannel SQUID Controller Front Panel 12 ree 5 Menu a EE 15 Fig r RE EEN 16 Figure 7 Multi channel Barchart SON at uae eddi 18 Figures Setup Kaz ee nn mn aa e Ra dee 18 Fig re 9 Remote VOM A A AR 19 Figure 10 Digital Data Acquisition Screen 19 Fig re Manual Tune Ee o 20 Figure 12 Reset Configuration Men Eege 21 Figure 13 Display Configuration enge et 22 Figure 14 System Default MO deer eebe 22 Figure 15 Heater Status ri henanemn nanas 24 Figure 16 Misc Settings Met uri 24 Figure 17 A tot ne SO nn nina nent nanas As 25 Figure 18 FEL Block DRASS RS taeda nn ni ou dde 35 Figure 19 Slew Rate o vs Frequency sn naine dinde 39 Figure 20 iFL 301 Pigtail Connector Pinout Face View 75 Table of Tables Table 1 Data Acquisition Rates vs Channel Configuration 20 Table 2 FEL Specifications A 36 Table Gain VS Range EE 37 Table 4 System Performance for SQUID with Open Input Col 38 Table 5
81. t parameter is the value 1 or 0 indicating if auto reset is turned on or off for that channel The second parameter is a value between 4 5 and 4 5 indicating the reset voltage Example QARESET 1 0 0 0 Description Inquire about the current auto reset settings for channels 1 3 Related Commands SARESET QDACQ Format QDACQ iMAG Response Returns a 6 byte ASCII character string with 2 parameters each ended with a semi colon Parameter is the channel configuration parameter 2 is the composite data acquisition rate Example QDACQ 1 3 Tristan Technologies Page 50 MAG 303 Multi Channel SQUID System Description Inquire about the current high speed data acquisition channel configuration and rate Related Commands SDACQ SARM SDARM SRATE SDAPCK QDAPCK QDAPCK Format QDAPCK iMAG Response Returns a 4 byte ASCII character string containing a number from 1 to 400 This number corresponds to how often the SRQ line is set during high speed data acquisition For instance a rate of 100 means the iMC 303 will output 100 packets of data and then set the SRQ line A packet contains 16 samples 32 bytes by default You can change the packet size using the SRATE command Example QDAPCK 100 Description Inquire about the current high speed data acquisition SRQ frequency Related Commands SDAPCK SARM SDARM SRATE SDACQ QDAPCK QDPCHAN Format QDPCHAN iMAG Response Returns a 3 byte ASC
82. t to exhibit very periodic behavior that looks much like a sine curve The periodic nature of the SQUID allows it to be used as a very sensitive magnetic detector These periods are expressed in terms of Do or Flux Quanta As the MODULATION level is incremented the voltage level and bar graph displayed will slowly increase reach a peak and then begin to decrease Up to five peaks in the voltage out will be seen as the MODULATION is incremented from 0 to 100 The first peak that with the lowest MODULATION level typically provides optimum SQUID performance 4 8 2 4 RESET CONFIGURATION The AUTORESET menu displays the status ON or OFF and the RESET LEVEL in volts for channels 1 3 AUTORESET CHANNEL 1 ON LEVEL 1 5 V CHANNEL 2 OFF LEVEL 1 5 V CHANNEL 3 ON LEVEL 0 00 V Figure 12 Reset Configuration Menu If ON is selected for any of the channels A SQUID RESET may be automatically triggered in one of two ways by the output voltage level exceeding the LEVEL value set in the AUTORESET menu or by an input signal exceeding 3V when the HIGH PASS FILTER is engaged The digitized channel output voltage is continuously monitored by software and if the signal level exceeds the range set by the user in the LEVEL field of the AUTORESET menu an automatic RESET is triggered Note that the setting of this voltage level parameter is dependent on the GAIN setting chosen in the RUN display If this voltage value corresponds to less than 0
83. te Electronics The iFL 301 Flux Locked Loop contains advanced hardware designs for signal amplification and conditioning in a compact package e Flexible Connections from the iFL 301 Flux Locked Loop to the SQUID sensor are provided via flexible shielded cable permitting numerous sensor positioning options Tristan Technologies Page 2 iMAG Multi Channel SQUID System e Digital Control The iMC 303 Multichannel SQUID Controller is based on a 32 bit microprocessor operating at 16 MHz to implement advanced signal processing techniques control and data acquisition e Auxiliary Channel An Auxiliary Channel provides a means for processing an external signal and synchronizing it with the data from the SQUID channels This can be used with a cryogenic level meter or for acquiring data from external sources e Accurate Use of a 16 bit dual channel Analog to Digital converter ensures accuracy and high speed The converter inputs are multiplexed to accommodate the 3 SQUID channels and the Auxiliary Channel e Fiber Optic The iMAG composite cable uses optical fiber communication to the iFL 301 Flux Locked Loop to eliminate grounding and shielding problems that often affect SQUID electronics e Autotuning An Autotune function determines optimum SQUID operating parameters with the touch of a single key on the front panel e Remote Control The iMC 303 Multichannel SQUID Controller is designed for incorporation in automated systems using eit
84. th RS232 These commands are broken down into 3 major types 1 GPIB common commands XXX These types of commands always have a as the first character and do not have a as the fifth character 2 Generic GPIB query commands XXX These types of commands always have as the first character and as the fifth character 3 IMAG device dependent commands If the command is not a GPIB common or GPIB query command this function is assumed to be an iMC 303 Multichannel SQUID Controller command e g SHPF QSAMP 1 Some of the iMC 303 Multichannel SQUID controller commands have more than 1 parameter The separator between the parameters is an ASCII comma and the terminator is an ASCII semicolon For input spaces CR and LF characters are stripped out by the parser You may use them when appropriate to make your source code more readable The character string returned by the iMC 303 in response to a query is terminated by a semicolon character and a linefeed n character and is not null terminated CAUTION There is NO separator between the command and its first parameter Reference Please refer to the IEEE Standard Codes Formats Protocols and Common Commands manual ANSVIEEE Std 488 2 1987 for the definition and intent of IEEE Common Commands and IEEE Common Queries Appendix B contains sample programs with both RS232 and GPIB protocol Tristan Technologies Page 42 MAG 303 Multi Cha
85. til ibrsp TC_handle amp statbyte SRQ line is set ibrd TC_handle inbuf 3200 read buffer of data process data here process and write to file count ibentl add bytes read to count ibwrt handle SDARM 6 disarm data flow Further Information For more detailed information on iMAG commands see Appendix A Appendix B provides some sample C language programs to help you get started For information on GPIB IEEE 488 products and software please contact National Instruments directly Tristan Technologies Page 73 MAG 303 Multi Channel SQUID System Appendix D SQUID Interface Connector Pinout Appendix D SQUID Interface Connector Pinout 0 000 FACE VIEW Figure 20 iFL 301 Pigtail Connector Pinout Face View Table 7 iFL 301 Pigtail Connector Pinout Face View Note The connector shell twisted pair shields and cable shield are grounded to the connector shell and a circuit board ground Tristan Technologies Page 75 iMAG 303 Multi Channel SQUID System INDEX A A D converter 40 AC Power 40 Analog Output 39 ANSIVIEEE Std 488 2 1987 42 Appendix A Remote Interface Commands 42 Appendix B Example Programs 65 Appendix C High Speed Data Acquisition 72 AUTORESET 21 AUTOTUNE 25 27 AUTOTUNE Key 12 Autotune Screen 26 Auxiliary Analog Input 39 Auxiliary Channel Connection 8 B Bandwidth Selections 38 Bench
86. time If it has already started to display the COOL DOWN TIME the HEATER ACTIVATION TIME should be increased slightly Start with a short time period such as 5 seconds and increase until the V signal at the Analog Output BNC is at the 0 volt level for a few seconds before the COOL DOWN Time counter is activated The WAIT TIME AFTER HEATER should be set at a minimum of 15 seconds Tristan Technologies Page 23 MAG 303 Multi Channel SQUID System SQUID HEATER ACTIVATED PLEASE WAIT Heater On 23 THE SYSTEM WILL AUTOTUNE WHEN DONE Figure 15 Heater Status Screen 4 8 2 6 3 SUCCESSFUL TUNE VOLTAGE This field allows the user to set a minimum voltage level for the SQUID AUTOTUNE It is the peak RMS magnitude of the periodic V y signal observed at the Analog Output on the rear panel while in the MANUAL TUNE screen Upon each AUTOTUNE the tune result will be compared to this voltage level If the RMS voltage of the tuned SQUID is equal to or above this level the RUN menu will be automatically entered upon completion of the AUTOTUNE If the tune voltage is less than this level the MANUAL TUNE menu will be automatically entered upon completion of the AUTOTUNE 4 8 2 7 MISC MENU This menu allows the user to select the FLL clock source and to enable the AUTO INITIALIZATION feature MISC SETTINGS FLL MASTER CLOCK SETTING MASTER AUTO INITIALIZATION ON Figure 16 Misc Settings Menu The iMC 303 Multichannel SQUID Control
87. ues that are useful for operating SQUID systems 6 2 Determining the Voltage Flux Transfer Function V The Voltage Flux Transfer Function for each SQUID sensor is measured prior to shipment and is recorded on the test report However it is sometimes useful to re measure this parameter This can be accomplished by introducing an offset to the operating point of the SQUID while operating in the RUN mode of just over 1 then RESETTING the SQUID The change in output voltage will correspond to the voltage flux transfer function V for that particular GAIN setting 1 Assure the SQUID is TUNED and is operating in the RUN mode with the HIGH PASS filter set to OFF Monitor the SQUID output voltage either on the display or at the analog output for the channel being used 2 There are a few different methods to introduce offset in order to achieve a 1 change One method is to use the OFFSET adjust in the RUN menu Start by setting the GAIN to X100 OFFSET to 0 and pressing the RESET Key Refer to the SQUID Sensor or System Integration Test Report to determine the approximate NI value The output displayed on the iMC 303 front panel should be less than the quantity shown in the Test Report Note the actual voltage output Using the INC and DEC Keys change the OFFSET so that the voltage output on the display has changed by approx 20 more than the V O value described in the Test Report Press the RESET Key The change in the
88. ure 4 iMC 303 Multichannel SQUID Controller Front Panel 4 2 FUNCTION Keys 4 2 1 RUN Key Pressing the RUN key causes the iMC 303 Multichannel SQUID Controller to enter the RUN mode and show the normal operating display The MAG Controller will begin or continue controlling the SQUID sensors immediately using the parameters shown on the RUN menu display and from the most recent TUNE cycle 4 2 2 SETUP Key Pressing the SETUP key displays the main SETUP menu used to change the iMC 303 Multichannel SQUID Controller operating parameters The iMAG Controller will continue to operate the SQUID sensor until a parameter is changed which will directly effect SQUID control 4 2 3 TUNE Key The TUNE Key causes the iMC 303 Multichannel SQUID Controller to determine the optimum SQUID TUNE parameters for each installed channel and show the result in the AUTOTUNE Display The AUTOTUNE algorithm is executed regardless of the menu currently displayed and is a fully automatic feature Tristan Technologies Page 12 MAG 303 Multi Channel SQUID System 4 2 4 DATA ENTRY Keys The DATA ENTRY keys change the settings within each menu Entering data from the front panel is a straightforward process using the following keys 4 2 5 SELECT Keys The SELECT key moves the cursor indicated by flashing text around the display allowing the selected text to be changed Each time the SELECT key is pressed the cursor moves to the next position 4 2 6 IN
89. ve product covers or panels or operate without all covers and panels in place Do not attempt to repair adjust or modify the instrument this could void product warranty For service return the instrument to Tristan Technologies Inc or any authorized representative Do not operate this instrument in a volatile environment such as in the presence of any flammable gases or fumes Tristan Technologies Page iii iMAG Multi Channel SQUID System Table of Contents 1 Introduction to the IMAG Multichannel System 2 1 1 AMAG System Configuration EE 4 2 NTRS Ee NEE 5 2 1 Unpacking And np ia 5 LL Packing EE 5 2 2 Power REQUIF MENES EE 5 2 2 1 Instrument E 6 X22 Grondin eege dee d e e 6 23 Operating EE ut EE 6 2 3 1 Operating Temperature Range 6 2 3 2 eet in AUS EES 6 24 Rear ENEE 7 229 OV stem Eent 7 2 5 1 Composite Cable Connection sssssssssssesseesesseossessesresseessesressee 7 2 5 2 Cryogenic Cable Conner ii ii 8 2 5 3 Remote Interface Connections ori 8 2 5 4 Auxiliary Channel Connecttons 8 2 959 Clock e 8 2 6 Mounting The iMC 303 Multichannel SQUID Controller 9 2 6 1 Te te EE H 2022 Rack Mounting EE H 3 Initial Power Up and Channel Installation ci 10 A A 10 3 2 Connecting to the Tristan LTS SQUID Sensor 10 3 3 Cooling the Tristan SQUID E 10 3 4 Initial Power Up Sequence And Display 10 3 5 Channel Installation and Using IMAG cooooonoccnocccooonconnnconncconocnnn cono cconnccnnocnnos 11 4 iMC
90. verflow Under flow Related Commands QUERREG Tristan Technologies Page 63 MAG 303 Multi Channel SQUID System Appendix B IEEE 488 2 and RS 232 Example Programs Appendix B Example Programs Introduction The iMAG may be controlled remotely using either the RS 232 or GPIB IEEE 488 protocol All of the functions available on the front panel are also available via remote interface This allows you to write simple programs to control your iMAG or even create an instrument driver You can also perform high speed data acquisition using GPIB protocol Voltage samples can be acquired from all four channels at a composite rate of up to 20 000 samples per second To control your MAG using a computer you will need the following RS232 1 RS 232 cable GPIB 1 GPIB cable and 1 National Instruments GPIB IEEE 488 card or equivalent For high speed data acquisition applications with GPIB we recommend using at least an IBM PC compatible computer with a 486 33 MHz processor or equivalent processing power DISCLAIMER Tristan Technologies Inc IN NO WAY ATTEMPTS TO REPRESENT OR RECOMMEND NATIONAL INSTRUMENTS PRODUCTS IF YOU HAVE ANY QUESTIONS CONCERNING NATIONAL INSTRUMENTS PRODUCTS PLEASE CONTACT NATIONAL INSTRUMENTS DIRECTLY Tristan Technologies Page 64 MAG 303 Multi Channel SQUID System GPIB Notes The following table illustrates the GPIB configuration GPIBO accessed by executing the National Instruments pro
91. voltage output on the display will reflect the actual Voltage Flux Transfer Function NI 0 3 Another method of offsetting the SQUID operating point is to use a simple magnet Remember that the shielding around the SQUID and the strength of the magnet have a major impact on the effectiveness of this technique To offset the SQUID slowly move a magnet closer to the sensor while observing the voltage output When the output reaches a level greater than the recorded Voltage Flux Transfer Function V 0 place the magnet in a stationary position The magnet must remain stationary Press the RESET Key Again the change in the voltage output on the display will reflect the actual Voltage Flux Transfer Function V 6 3 RF Interference and Shielding The SQUID sensor is sensitive to electromagnetic interference Interference may enter the system in a number of places such as the cabling improper grounding of instruments in the test setup and the SQUID input circuit The iMAG has been specially designed to minimize the effect that interference has on the system The majority of the interference does enter at the input of the SQUID Tristan Technologies Page 30 MAG 303 Multi Channel SQUID System Monitoring the Analog Output while in the MANUAL TUNE menu see Section 6 2 is a good diagnostic of the effect that interference is having on the system The output should be a clean signal with a peak to peak amplitude of the same magnitude as r

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