2126 Constant Fraction Discriminator User`s Manual
Contents
1. mended The external cable length estimated on the basis of 4 8 ns per meter for RG 58 cable would be L External Delay _ Total Delay Internal Delay 7 4 8 J 4 8 _ 3 0 0 3 ns 56 3 cm 22 in 4 8 ns m Walk Trim The adjustment of the amplitude sensitive variation of the timing mark time walk in the Constant Fraction and CFRR modes remains a less exact procedure Proper adjust ment is possible only when the dc offset present on the input to the 2126 is less than 6 mV dc Thus detector leakage or dark current errors must be minimized before at tempting adjustment 11 Operation 12 Laboratory trimming of the unit can be demonstrated by using a suitable pulse genera tor with a known fast clean wavefront and a delay chosen as discussed above A very broadband 50 ohm attenuator such as the Hewlett Packard HP 3496 or one whose time walk is very precisely known should be used An externally triggered oscillo scope capable of displaying at least 1 ns division is also necessary Step attenuations should be then yield a stable time position of the 2126 s output signal when starting from a reference 5 V peak pulse input Care must be taken that the pulse generator offset is small and does not change for different attenuatcr settings The WALK ADJUST trimming potentiometer can be used to find the best adjustment of the finite time walk over a narrower amplitude range as desired When the 2126 is used with the in2. 49 c oere Bde be EA RR ER ERD EOE EOS REE ROE EE EO 19 Typical CablesLengths RG 58 e ea isa we Eee e a a ee 20 Power Requirements io corriera Aa awa aS 20 Physical osc won a ate ce a eR aie A es ay LM A wea ee ew ah A ae ea 20 B Installation Considerations 21 1 Introduction The Model 2126 is a 200 MHz Constant Fraction Discriminator in a single width NIM It has independent controls for threshold walk output pulse width and operat ing mode and provides maximum flexibility for use in any timing application The 2126 is fully de coupled and provides two operating modes for use over a wide range of input count rates In the standard operating mode the 2126 operates to 150 MHz with the front panel potentiometer controlling both the output width and the internal dead time Alternatively a special high rate operating mode can be selected which provides operation to 200 MHz typically 250 MHz with fixed output width and dead time The 50 Q input of the 2126 accepts negative pulses with amplitudes up to 5 V Input protection is provided for inputs outside the expected range An internal jumper can connect a X2 attenuator to each input to extend the input range to 10 V A plug in module provides a means of changing the constant fraction factory set to 40 In ad dition to its normal Constant Fraction CF timing mode the 2126 provides a Constant Fraction with Slow Risetime Reject SR timing mode the S
3. Typical input signals to the 2126 are generated by a scintillation detector using a photomultipiier tube or a solid state detector with a charge sensitive preamp and tim ing filter amplifier Such signals are negative going from a baseline of ground Risetimes can vary from 1 ns to greater than 100 ns and widths from 1 ns to greater than 500 ns For the laboratory test bench a logic pulser can be used as an input to the 2126 See Figure 6 for a typical input signal produced by a logic pulser Figure 6 Typical Input Signal Produced by a Logic Pulser Operation Operating Mode Selection of operating mode depends or the requirements of the given experiment Some general compromises worth considering are discussed in the following para graphs Constant Fraction CF Mode In the Constant Fraction CF mode timing is derived from a comparison between a fixed ratio 40 in the 2126 and the peak amplitude of each successive pulse This in stantaneous self reference yields a time mark that is theoretically independent of the pulse height as contrasted to the behavior of the leading edge mode In the 2126 the ratio reference signal is taken internally and the full amplitude pulse is delayed for the comparison by an external cable connected between the two front panel DELAY con nectors When the length of this external cable is chosen to generate a time delay less than the rise time of the input pulse the resulting time mark is stabilized
4. for both amplitude and rise time variations of that pulse This is the basis for ARC Amplitude and Rise time Compensated timing The compromise in Constant Fraction and also ARC timing is the ability to provide proper delays for the rise time of the input pulse considering either rate and pileup ef fects or the distortions introduced by varying wavefront shapes due to charge collec tion deficit ballistic effects or trapping effects in the detector It is these accommodations that lead to empirical determinations of the optimum delay cable length for a given detector and setup Constant Fraction With Slow Risetime Reject SR Mode In the Constant Fraction with Slow Risetime reject SR mode a further accommoda tion is offered for the longer rise times of solid state detectors The timing mark for the Constant Fraction is derived from the slightly delayed pulse with the presumption that the THRESHOLD level has been set quite low and this level is exceeded prior to the derivation of the timing mark In the case of solid state detectors where long varying wavefronts of the input pulse are common a relatively short delay cable is frequently used and the above timing premise may not be satisfied In that case the amplitude discriminator keyed to the THRESHOLD setting may switch late and the resulting timing will represent some mix of the intended Constant Fraction timing with Leading Edge timing This effect causes either tailing or a sat
5. in connection with such equipment such as site supervision and installation services relating to the equipment shall be free from defects for a period of one 1 year from the date of performance of such services If defects in materials or workmanship are discovered within the applicable warranty period as set forth above we shall at our option and cost A in the case of defective software or equipment either repair or replace the software or equipment or B in the case of defective services reperform such services LIMITATIONS EXCEPT AS SET FORTH HEREIN NO OTHER WARRANTIES OR REMEDIES WHETHER STATUTORY WRITTEN ORAL EXPRESSED IMPLIED INCLUDING WITHOUT LIMITATION THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR OTHERWISE SHALL APPLY IN NO EVENT SHALL CANBERRA HAVE ANY LIABILITY FOR ANY SPECIAL EXEMPLARY PUNITIVE INDIRECT OR CONSEQUENTIAL LOSSES OR DAMAGES OF ANY NATURE WHATSOEVER WHETHER AS A RESULT OF BREACH OF CONTRACT TORT LIABILITY INCLUDING NEGLIGENCE STRICT LIABILITY OR OTHERWISE REPAIR OR REPLACEMENT OF THE SOFTWARE OR EQUIPMENT DURING THE APPLICABLE WARRANTY PERIOD AT CANBERRA S COST OR IN THE CASE OF DEFECTIVE SERVICES REPERFORMANCE AT CANBERRA S COST IS YOUR SOLE AND EXCLUSIVE REMEDY UNDER THIS WARRANTY EXCLUSIONS Our warranty does not cover damage to equipment which has been altered or modified without our written permission or damage which has been caused by abuse misuse acciden
6. loads through any rea sonable length of suitable 50 ohm coaxial cable such as RG 58 Figure 9 shows the typical negative output pulse shapes into 50 ohm loads with the WIDTH control set to minimum For optimum performance terminate unused negative outputs in 50 ohms 13 Operation 14 Figure 9 Typical Negative Output Pulses Into 50 Ohms Load Since the WIDTH control also sets the DEAD TIME following a given pulse in the NOrmal count rate range the user should set this control consistent with the pulse rate requirements of the given experiment In the minimum fully counterclockwise posi tion of the WIDTH control a count rate in excess of 150 MHz can be expected for the NOrmal mode of the 2126 The WIDTH control off the 2126 is inoperative in the High Rate mode The 2126 s positive logic outputs are designed to drive relatively high impedance loads with logic levels of nominally 0 and 5 V Since this type of output is inherently slower than current mode outputs the negative outputs the positive outputs may not provide proper logic transitions at the high count rates the 2126 is capable of Power Supply 5 Circuit Description The 2126 is a high performance Constant Fraction Discriminator in a single width NIM It also includes a power supply circuit to provide logic power to the unit This section describes the operation of both the power supply and the Constant Fraction Discriminator Power Supply The 2126 consists p
7. outputs each providing 2 V minimum into 50 Q rise time lt 10 ns pulse width controlled by WIDTH potenti ometer in Normal mode undefined in High Rate mode de coupled front panel BNC connectors Front Panel Controls 18 THRESHOLD Front panel 10 turn potentiometer to set acceptance threshold for in put pulses range 3 mV to 1 V TIMING MODE Front panel three position rotary switch to select constant fraction with slow rise time reject SR basic constant fraction timing CF or leading edge timing LE modes of operation WALK ADJUST Front panel potentiometer to compensate walk of the internal zero crossing discriminator Internal Controls WIDTH Front panel 10 turn potentiometer to vary internal dead time and width of negative outputs in Normal mode range 2 100 ns or 10 500 ns as determined by internal jumper Inoperative in High Rate mode Internal Controls ATTENUATION Board mounted DIP jumper selects no attenuation or X2 attenua tion of input signal FRACTION Board mounted DIP jumper selects value of constant fraction 0 4 stan dard other values available by special order OPERATING MODE Board mounted jumper selects NOrmal NO or High Rate HR operating mode OUTPUT WIDTH RANGE Board mounted jumper selects 2 100 ns X1 or 10 500 ns X5 output WIDTH range POWER SUPPLY Board mounted jumpers select 12 V or 6 V as input power for 2126 logic Performance DYNAMIC RANGE
8. under test During the design and assembly of the module reasonable precautions were taken by the manufacturer to minimize the effects of RFI and EMC on the system However care should be taken to maintain full compliance These considerations include e A rack or tabletop enclosure fully closed on all sides with rear door access e Single point external cable access e Blank panels to cover open front panel Bin area e Compliant grounding and safety precautions for any internal power distribution e The use of CE compliant accessories such as fans UPS etc Any repairs or maintenance should be performed by a qualified Canberra service representative Failure to use exact replacement components or failure to reassemble the unit as delivered may affect the unit s compliance with the specified EU requirements 21 22 Notes A CANBERRA Warranty Canberra we us our warrants to the customer you your that for a period of ninety 90 days from the date of shipment software provided by us in connection with equipment manufactured by us shall operate in accordance with applicable specifications when used with equipment manufactured by us and that the media on which the software is provided shall be free from defects We also warrant that A equipment manufactured by us shall be free from defects in materials and workmanship for a period of one 1 year from the date of shipment of such equipment and B services performed by us
9. 1000 1 WALK 50 ps 30 ps typical for a 1 ns rise time pulse over a 100 1 dynamic range referenced to 5 V in the CF mode COUNTING RATE Normal mode to 150 MHz as limited by dead time High Rate mode to 200 MHz PULSE PAIR RESOLUTION Normal mode lt 7 ns as limited by dead time High Rate mode lt 5 ns THRESHOLD STABILITY 2 0 02 C 200 ppm C TEMPERATURE RANGE 0 to 50 C THRESHOLD LINEARITY 0 25 integral 19 Specifications Typical Cable Lengths RG 58 For Plastic Nal and SSB detectors 0 3 to 1 0 m 1 0 to 3 3 ft For Planar Ge Detectors 1 0 to 2 0 m 3 3 to 6 6 ft For Coaxial Ge Detectors 2 0 to 4 0 m 6 6 to 13 ft Power Requirements Power jumpers set to 12 V 12 Vde 30 mA 12 V de 350 mA Power jumpers set to 6 V 12 Vdc OmA 6Vdc 30mA 12 Vde 12mA 6V dc 340 mA Exceeds the normal NIM power allotment of 167 mA for a single width module Physical SIZE Standard single width NIM module 3 43 x 22 12 cm 1 35 x 8 71 in NET WEIGHT 0 9 kg 2 0 Ib SHIPPING WEIGHT 1 8 kg 4 0 1b 20 B Installation Considerations This unit complies with all applicable European Union requirements Compliance testing was performed with application configurations commonly used for this module i e a CE compliant NIM Bin and Power Supply with additional CE com pliant application specific NIM were racked in a floor cabinet to support the module
10. DULE IN SPARE POSITION Figure 4 Constant Fractiion Module Including Resistor Values for Field Changes Count Rate Range Two count rate ranges are provided on the 2126 The user can select the desired count rate range by moving a jumper mounted on the circuit board NOrmal range NO is intended for most uses of the 2126 It provides for count rates up to 150 MHz In the NOrmal range the front panel WIDTH potentiometer controls the width of the nega tive and positive timing outputs and the internal deadtime of the 2126 Setup Information In certain extremely high rate applications the user should select the High Rate range HR This range provides for usable count rates of greater than 200 MHz However certain precautions should be observed in using the HR range of the 2126 In this range the front panel WIDTH potentiometer is inactive The width of the negative timing outputs and the internal deadtime of the 2126 are internally set at approxi mately 2 ns The input signal should be approximately 2 ns in width and show a clean return to the baseline in order to fully utilize the speed of the HR mode of the 2126 In addition the user should verify that companion NIM modules used with the 2126 in its HR range are capable of accepting negative NIM inputs of 2 ns width The NO HR jumper is located just to the right of A2 on the circuit board See Figure 2 NO is the upper position of the jumper HR is the lower position of the jumper Th
11. Model 2126 Constant Fraction Discriminator 9231701B User s Manual ISO 9001 SYSTEM CERTIFIED Copyright 2005 Canberra Industries Inc All rights reserved The material in this document including all information pictures graphics and text is the property of Canberra Industries Inc and is protected by U S copyright laws and international copyright conventions Canberra expressly grants the purchaser of this product the right to copy any material in this document for the purchaser s own use including as part of a submission to regulatory or legal authorities pursuant to the purchaser s legitimate business needs No material in this document may be copied by any third party or used for any commercial purpose or for any use other than that granted to the purchaser without the written permission of Canberra Industries Inc Canberra Industries 800 Research Parkway Meriden CT 06450 Tel 203 238 2351 FAX 203 235 1347 http www canberra com The information in this document describes the product as accurately as possible but is subject to change without notice Printed in the United States of America Table of Contents 1 Introduction acd oe wk he ee ae ee a ae 1 2 Controls and Connectors 2 2 oaae 2 ErontiBanel a tas Lo nS Se MO es UR BILAL he wes a es eee ie a 2 Internal Controls soe m an a de hehe eee e he Ses wade GMS eee 3 3 Setup Information es 4 Attenuator M
12. R mode rejects the slow rise time signals characteristic of some detectors thus improving timing performance Two independent fast negative timing outputs and two independent positive timing outputs are provided This provides maximum flexibility for most timing applications In addition a front panel LED indicates the presence of input signals The 2126 can operate from standard NIM bin 12 V and 24 V power supplies If a 6 V power supply is available the 2126 can be configured to use those supplies for most of its power requirements Controls and Connectors 2 Controls and Connectors Front Panel This is a brief description of the 2126 s front panel controls and connectors For more detailed information refer to Appendix A Specifications THRESHOLD CONTROL selects threshold for sig nal acceptance from 5 mV to 1 V INPUT accepts 5 mV to 5 V linear pulses 10 mV to 10 V with X2 attenuator in place Zin 502 OUTPUT LED indicates 2126 is processing pulses WALK ADJUST CON TROL varies relative zero cross timing to provide minimum time walk OUTPUTS Two inde pendent outputs provide 16 mA into 50 Q loads OUTPUTS Two inde pendent outputs provide 5 V nominal into high impedance loads mC DISCRIMINATOR Q 2126 Q THRESHOLD Figure 1 Front Panel MODE SWITCH deter mines timing mode SR Slow Reject CF Con stant Fraction LE Leading Edge WALK INSPECT OUT PUT d
13. a logic high When an input signal is applied the inverting output of A4a goes to a logic low when the input signal crosses the selected threshold voltage This logic transition occurs ahead of the output from the constant fraction comparator since the input to the constant fraction output is delayed by the front panel delay cable Thus the 10H209 OR NOR A3b gate has a high input from the threshold comparator and an indeterminant input from the constant fraction comparator prior to the application of an input signal When an input is ap plied A3b pin 7 goes low if the threshold is crossed Shortly later A3b pin 5 goes low due to the constant fraction comparator The inverting output ofA3b pin 3 goes high when the constant fraction comparator fires if the threshold was crossed This logic signal is the clock to the ultra fast 11C70D flip flop A2 When the 2126 is used in the Constant Fraction mode the D input of A2 pin 11 is held at a logic low by A3a pin 14 After the preceding signal was processed A2 was left in the SET state with the O output high and the Q output low When the clock sig nal arrives at A2 pin 7 from A3 pin 3 the D flip flop is RESET by clocking in the low at A2 pin 11 the outputs are active and the channel is unable to process further inputs A2 is SET via the HR or NO jumper thus terminating the outputs and the internal deadtime In the NOrmal mode of operation the Q output of A2 is pulled down by the current source co
14. ave our express permission to make one archival copy of the software for backup protection You may not copy our software or any part of it for any other purpose Revised 1 Apr 03
15. aws current is excess of the single width NIM module limit when connected to a 12 V supply operation of the 2126 from 6 V will reduce the current drawn to within the single width module limits If a 6 V power supply is available set the in put power jumpers to the 6 V position otherwise use the 12 V position See Figure 2 The 6 V position for both jumpers is towards the bottom of the module and is labeled B The 12 V position is toward the top of the module and is labeled A Standard Setup The Model 2126 is shipped from the factory in the standard configuration Attenuator module Fraction module Timing range Operating mode Output width range Power supply X1 no attenuation Constant Fraction F 0 4 NO normal CF constant fraction X1 1 100 ns 12 V Input Signals 4 Operation The 2126 is intended to be operated in a NIM bin equipped with a power supply pro viding 12 V and 24 V Alternately a NIM bin providing 12 V 24 V and 6 V can be used See Standard Alternate Power Supplies page 8 For lab bench testing a NIM power supply extension cable may be used However excessive voltage drops in the extension cable may be encountered due to the relatively high current require ments of the 2126 For use in experiments secure installation in a NIM bin is recom mended The NIM bin power supply should be off when the 2126 or other NIM are installed or removed from the NIM bin Input Signals
16. e 2126 is shipped in the NO position The Modes The 2126 provides three operating modes Constant Fraction CF Constant Fraction with Slow Reject SR and Leading Edge LE Refer to Operating Mode on page 10 for a description of the modes e The Constant Fraction CF mode is intended for use with detectors such as fast plastic detectors which exhibit fast rise time outputs with little risetime variation e The Constant Fraction with Slow Risetime Reject SR mode is often used with germanium detectors which exhibit a wide range of rise time variation e The Leading Edge mode is used with detectors which provide fast outputs with little amplitude or risetime variation CF and SR Modes Both Constant Fraction CF and Constant Fraction with Slow Risetime reject SR modes use the internal fraction module supplied with the 2126 To use either mode verify that the fraction module is properly installed in its socket near the front of the circuit board Figure 4 shows the proper installation of the fraction module With the fraction module installed the front panel Mode Switch allows selection of Constant Fraction CF mode or Constant Fraction with Slow Risetime reject SR LE Mode To select the Leading Edge Mode remove the Constant Fraction module from its socket near the front of the board and replace it with the Leading Edge module A socket is provided near the bottom of the circuit board to hold the unused module The fr
17. ellite peak in a time spectrum In the SR mode a logic alternation causes rejection of pulses which do not exceed the THRESHOLD prior to the derived Constant Fraction timing mark The result is en hanced timing resolution due to elimination of the Leading Edge errors but with some loss of counting efficiency 10 Delay Cable Leading Edge LE Mode The Leading Edge mode is used less often than the two Constant Fraction modes It is typically used for detectors with fast risetimes and little amplitude variation Since the Constant Fraction function is disabled when the 2126 is used in Leading Edge mode amplitude and risetime variation can introduce timing walk If the input signals are all essentially of the same amplitude and risetime the Leading Edge mode can offer good timing performance Delay Cable The delay cable used to set the Constant Fraction timing mark should provide a delay less than the known rise time of the applied input pulse for full compensation of both amplitude and rise time variations for a fixed shape For fast and moderately fast de tector pulses up to 10 ns rise time a delay of nominally 75 of the rise time is most effective For solid state detectors a delay of 40 of the pulse rise time is commonly used for the reasons given above The internal delay of the 2126 is 0 3 ns and this must be corrected by picking a suit able cable For example if the detector rise time is 4 ns a 3 ns delay would be recom
18. he X2 attentuation should be selected The attenuator module is a small assembly containing two resistors and a short jumper wire mounted near the front of the circuit board Figure 2 The attenuation factor can be changed by removing the module from the socket rotating it 180 degrees and re placing it in the socket Figure 3 illustrates the two choices of attenuation provided by the attenuator module The attenuator modules are factory set to the no attenuation position a NO ATTENUATION b x 2 ATTENUATION Figure 3 Options for the Attenuator Module Fraction Module Fraction Module In timing experiments one of the important variables to consider is the fraction of the input signal used to derive the constant fraction function Most applications provide optimum timing with a fraction of 0 4 This fraction is provided by the 2126 How ever the 2126 offers the user an easy means to change the fraction The fraction module is located immediately below the attenuator module near the front of the circuit board The user can change the desired fraction in two ways Figure 4 il lustrates the fraction module and lists values for two resistors that can be changed by the user to implement different values for the fraction Alternately contact the factory regarding other values of fraction modules available on special order P C BOARD EDGE PINI JP2 LEADING EDGE MODULE IN JP2 POSITION HETH 0 GR 0 HEZH Pn FRACTION MO
19. ip flop A2 The line driver receiver A1b is driven by the Q output of A2 and serves to drive the two independent negative outputs differentially It also toggles Alc the one shot driv ing the front panel LED The negative output transistors are conventional differential switches with the collectors driving the 50 ohm outputs directly A4 pin osv A4pin7 o svt A4 pin 15 1 0V Ma Figure 10 Timing Signals 17 Specifications A Specifications Inputs Outputs INPUT Accepts 5 mV to 5 V 10 mV to 10 V with internal X2 attenuator lin ear pulses rise time 21 ns Z 50 Q de coupled front panel BNC connector pro tected to 100 V duration limited DELAY Two BNC connectors between which a delay cable is connected to form the internal constant fraction signal Recommended lengths are based upon RG 58 cable propagation delay of 4 8 ns m 1 5 ns ft to provide a delay of 0 2 tase for germa nium detectors and 0 8 t for most other detector types rise rise WALK INSPECT Displays output signal of zero crossing discriminator for use in trimming time walk Z 50 Q front panel BNC connector NEGATIVE OUTPUTS Two independent negative current outputs each providing 16 mA into 50 Q rise time 1 ns pulse width controlled by WIDTH potentiometer in Normal mode 2 ns nominal in High Rate mode de coupled front panel BNC con nectors POSITIVE OUTPUTS Two independent positive voltage
20. isplays output of Constant Fraction com parator Attenuated ECL levels 85 mV and 190 mV DELAY CONNECTORS accept external delay cables Cable length determines delay WIDTH CONTROL varies width of outputs and sets channel dead time in NO Normal range Disabled in HR High Rate range Internal Controls Internal Controls Figure 2 shows the internal layout of the 2126 The function of the internal controls and their normal configuration is illustrated PC Board NOrmal or High Rate Jumper Plug E Tig A A JP3 JP4 ae power selection Jumper Plug A 12 V operation B 6 V operation Leading Edge Output Width Range Module in spare Jumper Plug position Front Panel Figure 2 Internal Controls Setup Information 3 Setup Information This section describes the function of the various jumpers and modules mounted on the printed circuit board of the 2126 Any adjustments should be made prior to install ing the 2126 in a NIM bin or connecting the 2126 to a power source Remove the left cover of the 2126 to expose the circuit board Attenuator Module The 2126 is provided with an input attenuator module This module provides the choice of no attenuation or X2 attenuation of the input signal The input range of the 2126 is 5 mV to 5 V If the peak input signal is expected to be 5 V or less no at tenuation should be selected For applications where the peak input signal is between 5 V and 10 V t
21. nsisting of Q9 and associated bias resistors The line driver receiver Ala senses the falling edge of A2 pin 2 and drives the SET input of A2 high thereby SETting A2 and terminating the output The front panel WIDTH potentiometer varies the current source Q9 and thus varies the rate of fall of A2 pin 2 Thus the width of the one shot formed from A2 is varied In the High Rate mode the current source Q9 and Ala are bypassed The rising edge of A2 Q is coupled directly to the SET input of A2 Thus the propagation delays associated with A2 determine the output widths and the internal dead time In the Slow Reject mode the circuit functions virtually the same The D input of A2 is driven by A3a pin 14 which now has a low going logic signal driven by the threshold comparator through A3a A slight delay is provided by R14 and C7 For fast rise time signals the D input of A2 is low before the clock drives pin 7 high However slow rise time signals cause the threshold comparator to fire slightly later For these slow rise time signals the falling edge of the signal at A2 pin 11 arrives after the clock at pin 7 and a high is clocked into the flip flop Since the flip flop is already SET no change occurs at its output and the input signal is ignored Constant Fraction and Threshold Circuits In the Leading Edge mode the Constant Fraction comparator A4b is disabled in a state that permits the Leading Edge comparator A4a to generate the clock for fl
22. odule iv daga oo e e a e Bue ee a E E 4 Fraction Module atasco Dl bas pa gy eee te al ad nce a 5 Count Rate Range ce eee eh SSE oros EER ORE ETE REE ES Ee He A 5 Ne NIOdES rin ots Sse oat Dn eto SAAR Secs SUAS hte GL aes E 6 Output Width Range 0 8a 40 sea ee dee ee nad a e eG 7 Standard Alternate Power Supplies 2 2 a 8 Standard SOUP vs ato ene te o are he a ee bg areas e oe Homey Gian Goons 8 4 Operation a oo a be ee we Ee ee we ES es 9 Input Signals ota ese Ae See ea RE OS owe ho BOM A pad OES DR aed 9 Operating Mode uri a ee es ee ee Dee ae a ee A eee a a 10 Constant Fraction CF Mode 2 snresk enert sts Korusa Sa 10 Constant Fraction With Slow Risetime Reject SR Mode 10 Leading Fdge LE Mode og iw a aod a Oe ee ke we 11 Delay Cable usaran a Shee eo OR ee Md we oe bw olde oe 11 Walk Trim cea a eee ie ee e ew Ee ee we ee 11 Threshold Adjustment lt 23 0 4 9 4 449d etaa BOG wa we gee e Bes eB ei a 13 Outputs and Width Control scssi eposda ae a a e ee 13 5 Circuit Description 2 a sosoo ee ee es 15 Power SUPPLY esus a aui a a Be a ia A 15 Constant Fraction and Threshold Circuits a a a 00008 48 15 PUS far on ee sh AA NN 18 OQutputSs e see EE HEE er He ODE HEE a ORE EER SE Ce ee a a 18 Front Panel Controls ss Rh bg aes aes See aos eee SPO bee Be ee gains 18 Internal Controls 4 4 Boa ecm andl Se Ae See Se Od RAO el eH ee ae eas Mages 19 Performance 2
23. ont panel Mode Switch should be set to Leading Edge LE Figure 5 shows the proper installation of the Leading Edge module Output Width Range PIN1 JP2 LEADING EDGE MODULE IN JP2 POSITION CTION MODULE IN FRA SPARE POSITION Figure 5 Leadilng Edge Module Table 1 summarizes the module and switch settings for the three operating modes Table 1 Operating Mode Summary F Front Panel Operating Mode Module Swltch Constant Fraction Fraction CF Constant Fraction with Slow Risetime Reject raci n oe Leading Edge Leading Edge LE Output Width Range Two ranges of adjustment are provided for the front panel WIDTH potentiometer Since the WIDTH potentiometer controls the output widths as well as the 2126 s inter nal dead time the proper range for the WIDTH adjustment should be selected Use X1 for fast plastic detectors and most sodiurn iodide detectors Detectors that provide in put signals of 100 ns width or greater or that cause baseline perterbations extending longer than 100 ns should use the X5 range The X1 X5 jumper is located below A2 on the circuit board See Figure 2 X1 is to the right and X5 is to the left The X1 X5 jumper is shipped in the X1 position Setup Information Standard Alternate Power Supplies The 2126 can operate from NIM bins equipped with the standard 12V and 24 V power supplies as well as those with the optional 6 V power supply Since the 2126 dr
24. rimarily of ECL logic which uses a supply voltage of 5 2 V In addition a TTL supply voltage of 5 0 V is required Two methods of obtaining these voltages are provided selectable by a jumper plug When the 2126 is used in a NIM bin with the standard supply voltages of 12 V and 24 V the logic supply voltages of 5 2 and 5 0 V are provided by adjustable three terminal regulators Q1 and 02 together with their associated circuitry provide stable well regulated logic voltages If a 6 V NIM power supply is available the circuit board s jumpers can be set to pro vide the required logic voltages directly from the 6 V supplies In each case a diode D1 for 6 V D2 for 6 V drops the power supply voltages to the logic voltages re quired by the 2126 In either case the 2 V ECL pull down voltage is provided by an additional three terminal regulator Q3 operating from the 5 2 V logic supply Constant Fraction and Threshold Circuits The input signal is applied directly to pin 10 of the threshold comparator D1 provides a temperature compensated voltage which is divided to produce 1 V across the threshold potentiometer RV 1 The wiper voltage of RV1 which varies from 5 mV to 1 V is applied to pin 10 of the threshold comparator The constant fraction function is implemented at the inputs of the ultrafast comparator A4b The input attenuator module is a X2 attenuator that maintains the proper 50 ohm input impedance It can be
25. rotated to provide no attenuation short between the input and pin 5 of the fraction module or X2 attenuation 100 ohms between the input and pin 5 of the fraction module The fraction module serves to attenuate both the prompt and delayed inputs to the constant fraction comparator A4b while providing the proper 50 ohm input impedance The prompt input to A4b pin 8 is attenuated more than the delayed input pin 7 resulting in the fraction f 0 4 This combination of at tenuation and delay provides the following signals at the inputs of the constant fraction comparator pin 8 0 3 input amplitude prompt pin 7 0 67 input amplitude delayed by cable selected 15 Circuit Description 16 See Figure 5 1 which illustrates the signals associated with the constant fraction and threshold comparators Prior to the application of an input signal the inverting output of A4b pin 2 can be in either logic state depending on the offset voltage applied to A4b pin 8 by the WALK ADJUST potentiometer Upon application of an input signal A4b pin 8 initially is lower than A4b pin 7 driving the inverting output A4b pin 2 to a logic high When the delayed signal arrives at A4b pin 7 it causes this pin to become more negative than A4b pin 8 which causes the inverting output A4b pin 2 to fall to a logic low The timing of this low going signal is input amplitude independent The inverting out put of the threshold comparator A4a pin 15 is normally
26. t neglect or unusual physical or electrical stress as determined by our Service Personnel We are under no obligation to provide warranty service if adjustment or repair is required because of damage caused by other than ordinary use or if the equipment is serviced or repaired or if an attempt is made to service or repair the equipment by other than our Service Personnel without our prior approval Our warranty does not cover detector damage due to neutrons or heavy charged particles Failure of beryllium carbon composite or polymer windows or of windowless detectors caused by physical or chemical damage from the environment is not covered by warranty We are not responsible for damage sustained in transit You should examine shipments upon receipt for evidence of damage caused in transit If damage is found notify us and the carrier immediately Keep all packages materials and documents including the freight bill invoice and packing list Software License When purchasing our software you have purchased a license to use the software not the software itself Because title to the software remains with us you may not sell distribute or otherwise transfer the software This license allows you to use the software on only one computer at a time You must get our written permission for any exception to this limited license BACKUP COPIES Our software is protected by United States Copyright Law and by International Copyright Treaties You h
27. tended detector timing resolution may be trimmed experimentally by successive measurements in the setup at hand A qualitative moni toring is available by monitoring the front panel INSPECT output with an oscillo scope For fast detectors the output should indicate an attenuated logic low ECL level approx 0 19 V dc into 50 Q where noise just disappears into this level and pulses are seen as transitions to logic high ECL approx 0 085 V do into 50 Q Reference Figure 7 Figure 7 Walk Inspect Wave Form Using Plastic Detectors Threshold Adjustment For slower detectors a noise band between the ECL levels may be seen with transi tions to ECL logic high and low of about equal intensity Reference Figure 8 Figure 8 Walk Inspect Wave Form for Slow Detectors Threshold Adjustment The 2126 threshold adjustment can be used as a lower level control to select the threshold above which input pulses will generate an output signal A front panel test point is provided to allow easy measurement of the selected threshold voltage As a general rule of thumb select a threshold voltage as high as possible while not exclud ing input signals of interest Unless experimental conditions dictate otherwise do not use minimum settings of the threshold since input signals often show ringing or base line perterbations which may generate unwanted outputs Outputs and Width Control The 2126 s negative logic outputs are intended to drive 50 ohm
Download Pdf Manuals
Related Search