1 The Quarknet/WALTA/CROP Data Acquisition (DAQ) Card
Contents
1. 75 ns gt 48 ns from trigger count at event start line 1 21 gt input 0 rising edge 0x01 gt 0 75 48 48 75 ns 01 gt input 0 has no falling edge 00 gt input 1 has no rising edge 23 gt input 1 falling edge 0x03 gt 2 25 48 50 25 ns 00 gt input 2 has no rising edge 01 gt input 2 has no falling edge 00 gt input 3 has no rising edge 01 gt input 3 has no falling edge 80EE004C 01 2A 00 01 00 01 00 01 0x80EE004C 2163081292 decimal gt 72 ns from trigger count at event start line 1 01 gt input 0 has no rising edge t 0 falling edge 0x0A gt 7 50 72 79 50 ns t 1 has no rising edge t 1 has no falling edge t 2 has no rising edge t 2 has no falling edge 00 gt input 3 has no rising edge 01 gt input 3 has no falling edge 5 80EE004D 00 01 00 01 00 39 32 2F 0x80EE004D 2163081293 decimal gt 96 ns from trigger count at event start line 1 00 gt input 0 has no rising edge 01 gt input 0 has no falling edge 00 gt input 1 has no rising edge 01 gt input 1 has no falling edge 00 gt input 2 has no rising edge 39 gt input 2 falling edge 0x19 gt 18 75 96 114 75 ns 32 gt input 3 rising edge 0x12 gt 13 50 96 109 50 ns 9 2F input falling edge OxOF gt 11 25 96 107 25 ns 28 Ouarknet WALTA CROP Card 11 23 2003 6 2 Appendix Brief history of card development Development of the2. Fig A3 pulse timing diagram of example C 24 Ouarknet WALTA CROP DAQ Card 11 23 2003 The next example is an actual event recorded by the DAQ card on Aug 8 2003 when we had a mini array of 4 counters set up In this example the card was set with d 6 w 10 the default startup values and for 2 fold or greater coincidence level Notice the data stream had 5 lines of data for this single event Example D 80EE0049 80 01 00 01 38 01 3C 01 7EB7491F 202133 242 080803 A 2 80EE004A 24 3D 25 01 00 01 00 01 7EB7491F 202133 242 080803 A 2 80EE004B 21 01 00 23 00 01 00 01 7EB7491F 202133 242 080803 A 04 2 0389 80 04 01 2A 00 01 00 01 00 01 7EB7491F 202133 242 080803 A 2 80EE004D 00 01 00 01 00 39 32 2F 81331170 202133 242 080803 A 2 04 04 0389 0389 04 04 0389 0610 The pulse timing diagram Fig A4 below shows the four PMT channels trigger bits vs time in nanoseconds Remember channels are numbered 0 through 3 Pulse edge times are recorded with 0 75 ns precision Recall however that the trigger logic works in time bins of 24 ns Fig 5 shows the channel trigger bits vs time in units of 24 ns The following sequence of events occurs 1 The first pulse arrives on channel 2 at t 1 in units of 24 ns Trigger gate 2 is set for 10 ticks The TMC records the pulse s leading edge at 18 ns relative to the last 24ns clock tick Three nanoseconds later a pulse arrives on channel 3 Trigger gate 3 is
3. delay this detailed timing information so that it is read out after the trigger is generated Then the card only needs to save information that happens when the gates overlap In the old days when NIM modules were state of the art this could not be done just by programming a chip It had to be done by splitting the signal using part of it for the trigger and sending the other part through long cables so that it arrived late after the trigger logic was firmly set in motion Consider the card s startup default settings d 6 and 10 Imagine a physics event where one pulse arrives three clock ticks after another The trigger will occur when the second pulse arrives so three clock ticks after the first the card detects trigger bit overlap and the TRG output goes high But internally pulse edge time information is delayed six clock ticks d 6 so the information about that first pulse is now available after just three more clock ticks the trigger is still on The information about the second pulse arrives after another three ticks again the trigger is still on Because both edges appear when the trigger is on they will appear in the data stream sent to the computer As an exercise for the reader using these default values and remembering that the width of the trigger varies depending on whether the pulses are close together or far apart what would cause a pulse edge to not appear in the data stream even though the card actua
4. 4 1 6 What major parts of 1 4 1 6 1 IDI THIN MO an 5 1 6 2 CPLD cU 5 1 6 3 PDCS 5 1 6 4 Microcontroller na bah bin Bb 5 1 6 5 GPS receiver ewes 5 Ouarknet WALTA CROP Card 11 23 2003 2 2d TEMPS STOLE dt nei BIA nte uem 6 2 2 An Aden ee tated RE inn 6 d etes J 24 AGP rc C NB BB ads 7 2 4 1 EP rig e M CE 7 2 4 2 CNS PPS SHO A i aout tt 7 2 4 3 How to calculate the event time ooWoWoWo WmoWoWoooWo W W 8 3 vOutput Data itti dieit ci etx sit suce i Ee cesi 10 Se TODTTIdE A co ds 10 d Use the acute esee tent i SAN KAN s ecce e den sug NAN 11 4l Basic coincidence deii eri inp RN NAN 11 42 GPS ODSetVatiOns esee tere caede aia eie sine a side eee ta 12 4 3 Measuring singles and coincidence rates oooooo 12 5 6 da a e verte Uo e d e Ea pra e anal ids 19 6 1 Appendix A Details of time and coincidence data handling 19 6 2 Appendix B Brief history of card development oooooo 29 6 3 X Appendix C Acronym and Jargon Dictionary 30 Quarknet W ALTA CROP Card 11 23
5. the elapsed time is long by a fraction of a second depending on how quickly you can enter the pairs of commands needed to start and stop 13 5 Figures Figure 1 a Block diagram of DAQ card b System hookup diagram Quarknet WALTA CROP DAQ Card 11 23 2003 QuarkNet DAQ card V 2 block PUSEEDGE ooo o TIMES COMP to DIGITAL threshold ae TRIGGER custom ab ea threshold PMT gt LOGIC _ LOGIC TIME CPLD uC RS232 gt to Computer a DIGITAL threshold 12 50 Port PMT3 MHz TIME Y O RdPAMP2 F COMP PLL t 1 3 333 ae fases DM aa a apenn a a 4 1 Internet PC serial port 12VDC to PMT igi d S 14 Quarknet WALTA CROP Card 11 23 2003 Fig 2 a Photo of card with components identified QuarkNet DAQ Board Layout CPLD Programmable fast logic Time to digital converter TMC Serial port Trigger output to PC output GPS input Reset switch Inputs for 4 counter 5V DC input signals Channels 0 1 2 3 Microcontroller Programmable slow logic interface b LeadTek GPS module with custom connector 15 Quarknet WALTA CROP Card 11 23 2003 Standa
6. 11 23 2003 6 3 Appendix Acronym and Jargon Dictionary Here are some abbreviations and terms used in this document One Pulse Per Second GPS signal used for precise time synchronization Alternating Current American Standard Code for Information Interchange Numeric code for text files S Application Specific Integrated Circuit A custom made chip like the TMC chips used in our DAQ card A Toroidal LHC ApparatuS a large international collaborative experiment at the Large Hadron Collider LHC at CERN Laboratory in Switzerland http atlas web cern ch Base 2 number system with only 2 digits 0 and 1 For example the decimal numbers 1 2 3 4 are written 1 10 11 and 100 in binary See also Hex below es j z gt gt 5 z z 2 gt A un Binary Digit Component of a number expressed in the binary system using Os and 1s only w A block of 4 binary bits which can store one ASCII character Unit of capacity for computer storage devices hard disks memory chips etc Either Bayonet Neill Concelman the inventors of the BNC connector or Berkeley Nucleonics Corporation opinions differ name for a commonly used connector for coaxial cable w In particle and nuclear physics a set of events that occurs simultaneously 1 within some small period of time For example 3 fold coincidence means particles are detected simultaneously in 3 separate detectors Complex Pro
7. 2003 1 1 1 Overview Development of the QuarkNet DAQ card was a collaborative effort involving Fermilab U Nebraska Lincoln and U of Washington Seattle See Appendix B for a brief summary of the project history 1 2 Purpose The Quarknet W ALTA CROP Data Acquisition card DAQ card for short takes signals from photomultiplier tubes PMTs and provides the kind of signal processing and logic that is basic to most nuclear and particle physics experiments Signals from up to 4 PMTs can be analyzed The board produces a record of output data whenever the PMT signals meet a pre defined trigger criterion for example when 2 or more PMTs have signals above some predetermined threshold voltage within a certain time window The output data record which can be sent via a standard RS 232 serial interface to any PC contains information about the PMT signals including how many channels had above threshold signals their relative arrival times precise to 0 75 nanoseconds and the starting and stopping times for each detected pulse In addition an external GPS receiver module provides the absolute UTC time of each trigger accurate to about 50 nanoseconds This allows counter arrays using separate DAQ cards for example different schools in a wide area array or two sets of counters at the same site to correlate their timing data Commands can be sent to the board to allow users to define trigger criteria select various options and retrieve a
8. DAQ card was driven by the need to provide a very low cost set of front end electronics to participants in school network cosmic ray detector projects Initially projects like CROP and WALTA supplied schools with NIM crates and modules on loan from Fermilab The loaned equipment had a book value of about 10K per school although in fact most of the modules were obsolete and no longer in demand for current experiments However off the shelf NIM modules to handle GPS timing data and interface to PCs in a simple way did not exist Thus while adequate for training and initial experiments by teachers and students these wide area network projects could not begin real data taking with the NIM hardware Meanwhile it was clear to engineers working in particle physics that for experiments like these with very small numbers of channels off the shelf fast electronics modules could be replaced with new programmable logic and time digitizer chips at very low cost At the request of Tom Jordan of Quarknet engineers Sten Hansen and Terry Kiper at Fermilab developed a prototype front end card for a simple table top cosmic ray demonstration detector This Version 1 Quarknet card put together components that were cheap and reliable but highly capable integrating on a single small board the discriminator logic and scaler functions of NIM modules for four PMT channels with a simple universal PC interface However only relatively coarse 20 ns pulse timi
9. set for 10 ticks The TMC records this pulse s leading edge at 21 ns Trigger gates 2 and 3 are set simultaneously so a trigger gate TRG is asserted If no further signals arrived the trigger would stay on for ten 24ns time bins 240 ns since the signals on channels 2 and 3 arrived inside the same clock tick In 24ns time bin 2 pulses arrive in channels 0 and 1 setting their trigger gates for 10 ticks Thus the 2 fold coincidence requirement is met continuously from time bin 1 until time bin 11 a total of 11 clock ticks or 264 ns shaded area in Fig A5 At the end of this interval the trigger gates for all channels are down so the TRG gate is dropped The pulse edge times stored during the time the trigger was on are read out of the TMC chip and reported Only edges that are within the trigger interval after they have been delayed by 6 ticks are put into the data stream Thus all the pulses in Figure A4 are recorded but the second falling edge of channel three which is off the figure to the right will fall outside the shaded area in Figure A5 and will not be recorded Note The actual values encoded in the data stream represent the delayed times If it is vital to get the actual time for each edge then each of them actually arrived d x 24 ns earlier than the time given in the data record Usually only relative timing matters and this kind of accuracy is not necessary The interpretation of the edge time data is explained in
10. singles will quickly overwhelm the card with the serial port set at 38 kbd trigger rates over 30 Hz cannot be handled When the card is set for two fold coincidences a trigger is declared any time that two or more channels trigger bits are 1 simultaneously If you set the card for three fold coincidence then it requires three channels with their bits set simultaneously and similarly for four fold However the trigger bits must overlap by at least one 24 ns clock tick to activate a trigger If one channel s bit drops and another rises no trigger will occur Also the trigger is active for exactly the overlap period The card has a TRG output that will go high when a trigger occurs you can watch this on the oscilloscope and see its duration change as the signals are closer or further apart The TMC Delay d is very different than the almost just like NIM coincidence described above The technical issue is this we don t just want to count triggers we also want to record all the edges that contributed to a given trigger It is hard to program the circuits inside the board to look back in time to the first pulse that contributed to the trigger when the second pulse might have arrived a significant amount of time later It was also hard to make the old NIM modules do this Instead we separate the thing that generates the trigger from the part that reads out the timing information and then we 20 Quarknet WALTA CROP DAQ Card 11 23 2003
11. unit s LED display blinks red when first powered up and searching and changes to steady green when it has acquired enough satellite data to locate itself accurately Time data are not accurate until then The GPS module provides several kinds of data The commercial GPS module directly supplies the date and coarse time in UTC not local time down to milliseconds or three decimal places after seconds and reports its geographic location in latitude and longitude down to the equivalent of a few 10s of meters 2 4 2 The 1PPS signal The stock LeadTek GPS module was modified slightly for our application to allow the more precise timing we need down to 10s of nanoseconds 8 decimal places following integer seconds The GPS receiver outputs a logic pulse at the beginning of each UTC second called the 1PPS 1 Pulse Per Second signal In principle the leading Quarknet W ALTA CROP Card 11 23 2003 edges of 1PPS signals from GPS receivers anywhere in the world are all in synch to within the accuracy of the non military GPS system about 100 ns This feature allows us to do accurate time synchronization between school sites The special connector and cable we attach to the commercial GPS module allows us to transmit the 1 PPS signal about 100 feet or more without excessive timing degradation 2 4 3 How to calculate the event time The way we get nanosecond accuracy is simple The DAQ card has onboard a simple cheap 41 667 MHz
12. 1 5 1 Serial data stream The DAQ board connects to your PC s serial port with a standard serial cable If your PC does not have a standard RS 232 serial port you can use a USB to serial converter available commercially 1 5 2 On board display The board has a 4 digit numerical display which advances when counting just to amuse your students By default it counts coincidence events since the last reset 1 5 3 TRG output There is an extra port which puts out a NIM standard logic pulse whenever a trigger occurs This can be used to trigger other equipment if desired at present it is not used in CROP or WALTA 1 6 What are the major parts of the system Fig 1 shows a functional block diagram of the DAQ card and Fig 1b shows how the counters and other components should be connected to set up a counter system Fig 2a shows a photo identifying the main components Quarknet W ALTA CROP Card 11 23 2003 1 6 1 Discriminators PMT signals are first pre amplified by a factor determined by a set of changeable resistors amplification factor x10 is used for Quarknet x2 by CROP x1 by WALTA Then discriminators are implemented using voltage comparator chips with the reference voltage adjustable via screwdriver adjustable trimpots Threshold levels can be set from 0 to 750 mV by adjusting each pot while monitoring voltage at a nearby test point Remember that the voltage comparators look at the amplifier output so raw PM
13. 1 The Quarknet WALTA CROP Data Acquisition Card R J Wilkes Hans Gerd Berns Richard Gran Univ of Washington Version 2b 23 Nov 03 Note This manual is a work in progress which attempts to compile information from many sources including technical documentation by Hans Berns Rik Gran Sten Hansen and Terry Kiper see http www phys washington edu walta qnet_daq and the practical experience of many other beta testers It is perpetually under construction Please send corrections and comments to wilkes u washington edu if you find errors or omissions Quarknet DAQ Card Development Team members e Fermilab Sten Hansen Tom Jordan Terry Kiper e U Nebraska Lincoln Dan Claes Jared Kite Victoria Mariupolskaya Greg Snow e U Washington Seattle Hans Berns Toby Burnett Paul Edmon Rik Gran Ben Laughlin Jeremy Sandler Graham Wheel Jeffrey Wilkes 1 The Quarknet WALTA CROP Data Acquisition Card 1 1 1 1 ooi ecu ien 3 V2 ee eee ree 3 13 Whatdoes the card do wanna 3 k4 What NN ANU 4 1 4 1 Power en 3 4 14 2 PMT sigalg NN 4 143 Qu 4 LS origeoer crore 4 1 5 1 Senaldata Sea sores 4 1 5 2 On board display ea akn Wana 4 1 5 3 TRO
14. 71 last IPPS 7EE62DDD y 2129014237 previous 1PPS 7C6A6587 208734759 1 must look back in datafile for previous R 2129014237 2087347591 41 666 646 ticks sec 7 _ 2129581371 2129014237 567 134 Ja 41 666 646 _ 41 666 646 tevenr SS 3 013611222 so this event occurred at 17 54 03 013611222 on 8 8 03 0 013611222 Quarknet W ALTA CROP Card 11 23 2003 3 Output Data Fig 4 shows the command summary obtained when you send the command elp Several of the commands will only be needed by experts Here we will focus on the commands highlighted in Fig 4 and their response formats 3 1 Output format Fig 5 shows screen shots with typical data displays as viewed in a terminal connected to the card Scaler data The command CD disables counters CE enables starts the counters and DS displays the counter contents in hexadecimal followed by a continuous record of event data as described below Scalers 0 3 store the singles rates for channels 0 3 and counter 4 records the number of n fold coincidences where n is whatever level you set These counts are running totals since the last time the counters were zeroed The reset commands RB reset counters and TMC only or RE reset everything including card setup parameters you may have changed will zero all counters Individual channel pulse data The command sequence CE DS will cause event records to be written as coi
15. F78 005533 AG F2PFF 00 28 91 98 98 98 98 98 98 98 98 98 98 98 a8 Read thermometer 802 2 Read scalers BBS D4CF19B4 DG Date Time 05 08 83 01 03 37 194 Display GPS data Status A valid PosFix 1 Latitude 47 39 2189 N Longitude 122 18 6513 W Altitude 14 9 Sats used 88 PPS delay 0571 msec 08229 FDCD CPLD time E13A CiS last 2 DEBE4291 DC4277EE1 CPLD freq 41667892 Hz 2 sec 41667091 Hz e Sample data running from terminal program on PC gt BA 2480 0 Request barometric pressure kReguest temperature at card 235 1 WCO4FF 7 Write to register 4 enable all channels 0004 003F v 4 L Start collecting trigger data 00 000016EA 01 00001EC2 card first reports its counter contents 02 000067E3 03 00000000 then data stream 04 0024E1E4 305 B25EBEOE B388F1B7 AE 01 3101 01 0001 B25EBEOE 195439 340 060603 V 00 2 0638 B388F 188 01 0001 37 32 2 00 01 B25EBEOE 195439 340 060603 V 00 2 0638 B388F 1B9 27 22 00 01 00 01 0001 B25EBEOE 195440 340 060603 V 00 2 0361 B388F1BA 00 01 31 34 0001 00 01 B25EBEOE 195440 340 060603 V 00 0 0361 etc 18 Quarknet W ALTA CROP Card 11 23 2003 6 Appendices 6 1 Appendix A Details of time and coincidence data handling This appendix is for users who want to understand the operation of the card in more detail Warning it gets technical
16. Fig A6 25 Ouarknet WALTA CROP Card 11 23 2003 Discriminator outputs c lt 10 20 30 40 50 60 70 80 90 100 110 120 nanoseconds Fig A4 Discriminator output timing diagram of example D Channel gates Channel E 8 24 ns time bin Fig A5 Channel gate timing diagram card trigger interval is shaded 26 Ouarknet WALTA CROP Card 11 23 2003 Fig A6 Interpretation of data records for example event See also http www phys washington edu berns WALTA Qnet2 misc DAQ output format txt 80EE0049 80 01 00 01 38 01 3C 01 7EB7491F 202133 242 080803 A 04 2 0389 80EE004A 24 3D 25 01 00 01 00 01 7EB7491F 202133 242 080803 A 04 2 0389 80EE004B 21 01 00 23 00 01 00 01 7EB7491F 202133 242 080803 A 04 2 0389 80EE004C 01 2A 00 01 00 01 00 01 7EB7491F 202133 242 080803 A 04 2 0389 80EE004D 00 01 00 01 00 39 32 2F 81331170 202133 242 080803 A 04 2 0610 5 data lines for this event the first line has a trigger tag in the REO number 2nd field is gt 80 followed by 4 lines without trigger tag 2nd field lt 80 In all 5 lines GPS date is the same 080803 August 8 2003 GPS status A valid Number of GPS satellites tracked 04 4 satellites DAQ status flag 2 in all 5 lines bit0 0 no 1PPS pulse pending bitl 1 trigger interrupt pending data in TMC not empty possible high rate if bitl is not 0 at end of event bit2 0 G
17. PS data OK bit320 CPLD frequency OK 1PPS count in lines 1 4 0x7EB7491F 1PPS count in line 5 0x81331170 gt difference 0x027BC851 gt CPLD freqency currently 41666641 Hz gt 1 CPLD cycle 1 41666641 sec 24 000014784 ns GPS time down to integer second of the 1PPS signal leading edge Delay is 389 milliseconds for lines 1 4 last field in the line round 202133 242 0 389 20 21 33 UTC Delay is 610 milliseconds for line 5 GPS time of the 1PPS pules in line 5 round 202133 242 0 610 20 21 34 UTC trigger count in line 1 0x80EE0049 gt difference from 1PPS count 0x80EE0049 0x7EB7491F hex 37140266 decimal gt time since last 1PPS pulse 37140266 24ns 0 891366384 seconds assuming CPLD frequency is the nominal 41666667 Hz gt absolute trigger time of this event 8 8 2003 20 21 33 891366384 computing the corrected absolute time by using the measured CPLD frequency of 41666641 Hz from consecutive 1PPS counts see above gt time since last 1PPS pulse 37140266 41666641 0 891366933 seconds gt absolute trigger time of this event 8 8 2003 20 21 33 891366933 So assuming the nominal frequency exactly 24 00 ns CPLD ticks would result in a 549 ns error in this example Pulse edge data line 1 80EE0049 80 01 00 01 38 01 3C 01 trigger count 0x80EE0049 2163081289 decimal REO 80 gt bit7 1 trigger flag for this event bit5 0 input 0 has no rising edge FEO 01 gt i
18. Status Display Scalar Fifo Counters 0 3 Triggers and 1 PPS Time Display Time Control Registers of TMC address 0 3 FL Load Binary File FR Read SumCheck FC Copy to CPLD Init Link with GPS unit GGA 1 sec RMC 1 sec disable others HF Trigger format HS Status format HB Barometer format NMEA GPS Data Append n 1 On n 1 Off add GPS to output NMEA GPS Data Echo n 1 On n 1 Off GPS Baud 9600 RB TMC CPLD RE MSP430 TMC CPLD SA Save TMC CPLD Registers to Flash SA 1 Restore Defaults Set Baud Rate PC Link 1 19200 2 38400 3 57600 4 115200 Serial Number BCD SN Display Number SN nnnn Store Serial Number Send Status Data n 1 On n 1 Off See HF Thermometer Data Display 40 to 99 degrees C Write Counter Control Registers CPLD address mm with data nn Write Time Control Registers TMC address mm with data nn 17 Quarknet W ALTA CROP Card 11 23 2003 Figure 5 Screen shots showing results from common commands Screen shots Startup event data Guarknet Scintillator Card QNET2_U2 HEsHELP CLeClear Screen 1F836D3B AB 01 66 01 00 01 BA 01 IDCD78ED 885526 219 058883 A 88 A 0543 12936065 Al 35 88 01 BH 01 A 01 1DCD7SED 885526 219 0508803 A 08 05 12036066 01 91 1DCD78ED 8 2426 C8E 68 22650015 8 24267037 91 22C58D15 24267C38 91 22658015 226581015 91 226581015 91 68 2N386B51 61 68 2N386B51 61 20386851 91 2F2FFF78 005533 2F2FF
19. T signal levels are multiplied by any amplification factor present For example if you used 30 mV threshold with NIM discriminators and have x2 amplification your threshold level on the DAQ card should be set to 60 mV To avoid damage to the trimpots use only the special sleeved screwdrivers supplied 1 6 2 CPLD Trigger logic is implemented using a CPLD Complex Programmable Logic Device chip Software revisions for this chip must be prepared using special software but can be then downloaded via the serial port allowing us to distribute updates that alter the fast logic if necessary Any trigger logic level from singles to 4 fold can be set by commands to the card Majority logic is used any combination of 3 active channels causes a trigger at the 3 fold level for example 1 6 3 TDCs Discriminator output pulses are fed into TDCs Time to Digital Converters which are used to measure the arrival time of leading and trailing edges of pulses They keep track of their state high or low at 0 75nstime intervals If the trigger criterion is satisfied the TDC data are latched and read out giving leading and trailing edge times for each channel relative to the trigger time in units of 0 75 ns This allows us to calculate PMT pulse widths Time Over Threshold or TOT see Fig 3 as a crude estimate of pulse area Note TDC is a generic term in particle physics technology The specific chips used on the board were named TMCs T
20. W ALTA CROP Card 11 23 2003 4 Using the card Fig 1b shows how to hook up the components of your detector system Here we give simple command sequence recipes for common experiments 4 1 Basic coincidence counting We want to set up the card by disabling and zeroing the onboard counters and setting our desired values for the parameters d and w see Appendix A for details Note that d and w are in units of 24 ns The startup defaults are d 6 and w 10 which are good for muon telescopes For air shower detectors set d 50 and w 100 Reset the card to zero counters and set everything to defaults unless the card was just turned on RE Disable the counters and TMC CD Set the value of d TMC delay Set the time registers with read pointer register 01 00 and the write pointer register 02 to d in hexadecimal The TMC delay d will be the difference of these values so in fact you could set 01 to some value nn and 02 to nn d For example if we want d 6 WT 01 00 WT 02 06 To get 4 50 ticks we would set register 02 to 32x 5010 The maximum is 7 12710 Set the coincidence level and enable desired channels Set control registers with the WC Write Control register command Register 0 sets the coincidence level using its first left hex character Here 0 means singles 1 means 2 fold and n 1 means n fold coincidence level is to be required The second right hex character represents the desir
21. characters 0 9 and A F or a f to represent numbers with decimal values of 0 to 15 Widely used in computers since one hex digit represents 4 binary bits and data storage in bytes of 4 bits or multiples of 4 8 16 32 etc is very common Example A37F hexadecimal 41855 decimal 1010 0011 0111 1111 binary KE Koh Enerhughi Ken Kyu Sho High Energy Accelerator Research Organization Tsukuba Japan http www kek jp intra html Japan s equivalent to Fermilab L Light Emitting Diode LEMO Company name Miniature coax cable connectors same function as BNCs MCU Micro Controller Unit See also CPU N Nuclear Instrument Module A standard for interchangeable nuclear physics electronics modules dating back to the 1950s AL K U ex D IM NMEA National Marine Electronics Association commonly used data specification with navigation instruments e g GPS receivers NSF National Science Foundation http www nsf gov nanosecond 1 billionth 10 of a second Op Amp Operational Amplifier an integrated circuit element that amplifies a 31 Quarknet W ALTA CROP Card 11 23 2003 signal Op amps are the building blocks of many kinds of digital circuits ee Computer generic term covers Windows Mac or Linux boxes Photo Multiplier Tube Vacuum tube that converts extremely low light levels down to a single photon into electrical signals Science outreach program
22. dapter is shown in Fig 2c Parts shown in the wiring diagram can be obtained at any electronics supply store The LED is optional and just blinks to display the IPPS signal indicating valid data The GPS module itself is weatherproof but the connectors should be protected Also we find the screws on the cover of the GPS module tend to rust so they should be covered with plastic paint or nail polish before deployment outdoors 1 6 6 Auxiliary sensors There is a temperature sensor built into the microcontroller chip so CPU temperature can be measured This temperature and the supply voltage are reported whenever the board is started up While the board components are rated for temperatures between 20C and 80C the board temperature should not normally go above about 50C A second temperature sensor is located on the booster board built into the GPS cable s far end DB9 connector i e about 3 feet from the GPS module This can be used to log outdoor temperature at the counter locations for example This sensor is read out with a special command as described below A barometric pressure sensor is built into the board Details on its use will come later 2 Functionality The way the DAQ card defines event triggers differs subtly from the way the NIM coincidence units work Please read the following carefully 2 1 Threshold detection As mentioned the PMT signals are fed first to amplifiers then to voltage comparators The co
23. dditional data such as counting rates auxiliary GPS data and environmental sensor data in addition to trigger and PMT pulse information 1 3 What does the card do First the DAQ card replaces the functions of the NIM electronics used initially in CROP and WALTA It effectively provides discriminators and trigger logic for 4 channels of PMTs The board includes 5 built in scalers allowing simultaneous counts of singles on each channel plus triggers at whatever logic level the user specifies 2 to 4 fold majority logic These counters can be zeroed and then read out upon command The DAQ card provides other functions not supplied by our NIM electronics There is a simple standard RS 232 interface which should work on any PC Windows Linux or Mac The data stream consists of simple ASCII text lines which should be readable by any terminal emulator program In addition a GPS clock provides accurate event time data synchronized to Universal Time UTC so widely separated sites can compare data In data stream mode the DAQ card outputs a series of text lines reporting event data trigger time in UTC with 24nsresolution and absolute accuracy about 100 ns leading and trailing edge times for each pulse recorded within the coincidence time window with 0 75nsprecision and data from the GPS and internal clocks Additional commands to the board allow temperature and barometric pressure sensors to be read or download GPS housekeeping data suc
24. e of arriving particles to be between 10 m and 200 m thick so the earliest and latest particles might arrive at our counters about 0 6 microseconds apart for a vertical shower Thus we want to have be about 1 microsecond can be about the same So we might want to set d 50 1 2 microseconds and w 100 However we should not set huge time windows just to be safe or the card will be busy all the time and its effective dead time will become a serious problem The values of dand w should be kept as small as possible consistent with the given physics goals Default values effective when the card is powered up are d 6 1 144 ns and w 10 240 ns These values are optimal when the card is used for a muon telescope experiment but for air shower detectors larger values are preferable and must be set by the user We suggest using values of d 50 and w 100 for air shower detectors as in the example above Now back to the details that go into the formula for d and w Whenever an above threshold voltage is detected on any channel that channel turns on an internal trigger bit for w clock ticks w x 24 ns At the end of that time the internal trigger bit is reset to zero The card s startup default setting is for 1 fold coincidence which means it will trigger on singles any above threshold signal on any channel produces output data Unless your PMTs are extremely quiet actually triggering on
25. e channels not just for the 2 channels that launched the trigger with empty data entries for channels that remained inactive during the trigger window For a single event trigger the DAQ card may need to output several lines of data depending on how many pulses are present in the event The first line has an event flag for identification Any following lines without this flag are simply additional data for the same event 2 3 Rate counters The card has 5 built in counters numbered 0 through 4 which work just like NIM scalers Counters 0 through 3 record the singles count for each channel and counter 4 records the trigger count for whatever coincidence level you have set By zeroing these counters with a software command then running the card for a fixed length of time and reading out the counters at the end you can obtain singles rates for each channel and the rate of coincidence events 2 4 GPS data 2 4 1 GPS startup Once powered up the GPS module should quickly find itself if it is in a location with a clear view of about half the sky or more Usually it does not work well through windows and should be physically outdoors but in some buildings it can be left on a windowsill The receiver will lock onto 4 or more satellites download the data needed to operate accurately and start averaging its position and clock settings at one second intervals Within a few minutes after startup you should have accurate GPS data The
26. e story There is an additional delay of 150 250 millisec which is unresolvable since it is buried in the manufacturer s firmware Luckily it is too small to cause the rounding procedure described above to go wrong Remember all this is just about determining the integer seconds part of the time Nanosecond level timing is not affected Also we have not discussed corrections for the antenna cable delay the event time calculated is when coincidence occurs at the DAQ board not at the counters This is of no consequence as long as all school sites in an array use approximately the same cable lengths within a few 10s of meters Here is an algorithm showing how to get the precise event time teourse hh 55 555 mm dd P delay 0 ddd integer seconds ss round ss sss 0 ddd to nearest second clock count at time X Clock rate ipes N previous ipps ticks sec N TRIGGER N LATEST 1pp3 SS 1 Alternatively use second running average for the clock rate Inanosec CN Luresr 1 previous iPPS m K The following example illustrates this calculation EXAMPLE 7EEED53B 36 30 00 01 00 01 7EE62DDD 175402 082 080803 V 00 0 0887 hh mm 55 555 217 54 02 082 ss sss 02 082 887 0 ddd 0 887 ss 2 082 0 887 2 969 round gt ss 03 trigger 7EEED53B py 21295813
27. ed pattern of enabled disabled channels in its bits with Os for disabled channels and 15 for enabled channels Thus for example WC 00 1 means set 2 fold coincidences with all 4 channels enabled Fy 1111 If you wanted to disable channel 2 you would use 1101 Dy So to enable 3 fold coincidences with channel 2 turned off you would use WC 00 2D Set the value of w gate width Registers 2 and 3 hold the gate width setting in integer clock ticks units of 24 ns Just to confuse you the lower 8 bits of the binary number representing w go in register 2 and the higher 8 bits in 3 So if abcd is the desired gate width w in hexadecimal we would use WC 02 cd 11 Quarknet W ALTA CROP Card 11 23 2003 WC 03 ab For example to get w 100 clock ticks 1001 00644 0000 0000 0110 0100 notice how handy hex is for representing binary numbers compactly WC 02 64 WC 03 00 Re enable the onboard counters counting will begin immediately CE When done counting to read out the counts first stop the counters CD Then read and display their contents DS 4 2 GPS observations To read out the current GPS time latitude longitude altitude and number of satellites in view GP Note You can directly monitor the GPS module s serial data stream by sending the command NM 1 This command will pass all data from the GPS module directly to your PC Normally the board s MCU reads interprets and distill
28. fast To keep the cost low our great engineers created a very clever scheme for handling the tasks we need with minimal resources Of course clever also means not simple For this reason the way in which triggering is handled differs in some details from what one would expect from simple modular fast electronics like NIM coincidence units The card handles coincidences as described below We define define two parameters which the user can set 1 w Gate Window just like the width setting in a NIM module it determines how close together pulses must be to cause the card to trigger Note in digital electronics the term gate means a signal used to enable open the gate for passage of other signals or data 2 d TMC delay complicated to define precisely but it determines which pulse edges get read out into the data stream when a trigger occurs by delaying this information until the trigger actually happens Both w and d are measured in units of 24 nanoseconds the internal clock tick interval The meaning of w is familiar if you have used NIM coincidence modules before but both w and d will be explained below First we consider the actual physical quantities that interest us and then relate them to these two parameters maximum time window during which real physics processes we want to study might cause a trigger In other words if we set the card for 2 fold coincidences and one channe
29. funded by NSF and DOE http quarknet fnal gov RS232 Recommended Standard 232 commonly used for computer serial IL interfaces SALTA Snowmass Area Large scale Time coincidence Array http faculty washington edu wilkes salta P PMT QuarkNet Scaler TDC TMC TOT TRG UNL U Pulse counter Time to Digital Converter Time Memory Cell Name of the specific TDC chip used in the DAQ card see http research kek jp people araiy TEG3 teg3 html TOT Time Over Threshold Trigger In nuclear and particle physics the digital signal that indicates an event of interest has occurred and data should be logged University of Nebraska Lincoln Universal Serial Bus Universal Serial Bes Time GMT WALTA Washington Large scale Time coincidence Array http www phys washington edu walta 32
30. grammable Logic Device a general purpose integrated circuit chip which can be used in many ways as programmed by the user Central Processing Unit The heart of a computer Cosmic Ray Observatory Project http physics unl edu gsnow crop crop html Data Acquisition Serial Communications D Shell Connector with 9 pins E 9 c 5 eg 30 Quarknet W ALTA CROP DAQ Card 11 23 2003 DC Direct Current Discriminator In particle and nuclear physics an electronic circuit that produces an output pulse only when its input voltage exceeds a selected level US Department of Energy http www doe gov Event In particle and nuclear physics a coincident pattern of detected particles that is likely to be of interest and should be recorded Derived from the use of the same term in Special Relativity an occurrence at a particular point in space and time FIFO First In First Out type of memory buffer where data is taken out in the same order as it s put in FN Fermi National Accelerator Laboratory also known as Fermilab http www fnal gov FPGA Field Programmable Logic Array One variety of CPLD which see Gate In digital electronics a signal that enables another signal to be transmitted the digital equivalent of a toggle switch Global Positioning System http tycho usno navy mil gps html H Hexadecimal number system with base 16 Uses the
31. h as the number of satellites visible Quarknet W ALTA CROP Card 11 23 2003 1 4 What goes in 1 4 1 Power The board requires a stable 5 VDC power supply with 800 mA or greater capacity A modular 110VAC to 5V 2 4A modular switching power supply of the type used for many small electronic devices is supplied with the board Replacements are readily available at Radio Shack or similar stores NOTE it is important to distinguish these DAQ power supply modules from the 12V units used for the WALTA HV supply boxes which are very similar in appearance Connection of a 12V supply to your DAQ card will probably fry it 1 4 2 PMT signals BNC coax connectors accept cables from the individual counters Note that the channels are numbered 1 2 3 and 4 on the board but we will refer to them as channels 0 1 2 and 3 This numbering scheme starting from 0 instead of 1 is consistent with engineering and computer programming practice get used to it 1 4 3 GPS data The external GPS module is connected through a special cable which has a seemingly standard D connector serial port connector on the far end This connector mates with the commercial GPS module s serial connector However the special cable s D connector actually contains a tiny circuit board with components needed to ensure good performance over 100 foot or longer cables The GPS clock will not work if the special cable is not used 1 5 What comes out
32. ime Measurement Chips by their designers and you may see this designation in some documentation 1 6 4 Microcontroller The microcontroller chip MCU it is really just a special purpose CPU provides the onboard slow logic with time scale microseconds not nanoseconds which interfaces the board to the user via a terminal window or equivalent on your PC At present the MCU can be reprogrammed to redefine functionality only by using special software and burn in hardware not a do it yourself project but at least the logic can be changed and updated if necessary 1 6 5 GPS receiver and interface The external GPS module Fig 2b is interfaced to the Quarknet DAQ board with a special cable which can be over 100 long if necessary Although the GPS module s RS Quarknet W ALTA CROP Card 11 23 2003 232 D plug appears conventional it has been modified with a special connector which contains the circuitry required to deliver DC power to the module and interface the 1PPS signal to the board This connector should not be inserted directly into your PC s serial port You may wish to use the GPS module alone for example to observe satellite data without operating the DAQ card For standalone operation of the GPS module you will need to construct a special adapter to allow connection of a SVDC power supply directly to the module you can use the same power supply used for the DAQ card The wiring diagram for the a
33. l gets a signal at t 0 at least one other channel must show a signal before t or we will lose detailed information about that pair of pulses See examples below the duration after the first pulse in a trigger during which we want to record all rising and falling edge times The channel in which these extra pulses occur does not matter all of them will be saved Then we should set the values of w and d as follows Set d gt Trpo but no smaller than two clock ticks Set w gt 1 For example if we want to build a muon telescope with counters less than a meter apart is the time it takes a muon to go from the top counter to the bottom counter traveling at the speed of light about a foot per nanosecond Thus Tra is only few ns so we should set d to the minimum value of 2 clock ticks or 48 ns Similarly to simply count muons we are only interested in a short time window for edges so we could take Twiptu 48 ns also Then we should set d 2 and w 3 19 Quarknet WALTA CROP DAQ Card 11 23 2003 However if we want to look for muons that stop and decay 2 2 microseconds mean lifetime in a third counter we need to look for the decay electron pulses several microseconds after the trigger so we should have Twrpru 400 9600 ns or about 10 microseconds Thus we would set d 2 and 401 As another example in extensive air showers we expect the main pancak
34. lly triggered The conclusion of this problem is that there might be information in the data stream that does not correspond to the physics processes we want to study On to some concrete examples 21 Quarknet WALTA CROP Card 11 23 2003 Here are three examples of event timing diagrams showing 2 fold coincidences with d 6 w 10 In each case pulses of width 2 clock ticks 48 ns arrive at inputs 0 and 1 but with different time separations in each example The timing diagrams show the discriminator output the channel trigger gate and the TMC output after delay d for each channel plus the coincidence trigger gate and the edge time information obtained from the TMC upon readout Example A Signal in channel 1 arrives 2 clock ticks 48 ns after signal in channel 0 Notice that the trigger gate is 8 ticks long overlap time of the two 10 tick channel gates All edges get reported Signal and gate timing input 0 gate 0 TMC delay 0 input 1 gate 1 TMC delay 1 2 fold TRG Edges 0 Edges 1 0 4 8 12 16 20 24 28 24 ns time bin Fig Al pulse timing diagram of example A 22 Quarknet WALTA CROP Card 11 23 2003 Example Signal in channel 1 arrives 3 clock ticks 72 ns after signal in channel 0 In this case the trailing edge of the delayed TMC signal for channel 1 lies outside the card trigger ga
35. lone adapter wiring diagram Construct this adapter to allow direct operation of the GPS module via a PC serial port without a DAQ card The LED is optional and simply blinks to display the 1PPS signal to indicate when the GPS module has locked onto a position and time fix SVDC power can come from a 110VAC adapter or a PC mouse jack Shown Power is taken from your PC or laptop s PS 2 mouse jack Power drawn is equivalent to what a mouse would consume and will not affect your computer You can substitute a connector to mate with a standard 5VDC power adapter available from any electronics store Coptional gt to from GPS Pi Di P2 Ri 1PPS 1 d 6 ik LED GPS TX 2 GPS RX 3 DOM DSub 9 pin male 16 Quarknet WALTA CROP Card 11 23 2003 Figure 3 Time Over Threshold TOT thresh Figure 4 Command list help screen Scintillator Card QNET2 Firmware Ver2 3 09 09 03 HE Help Serial 1002 Barometer Counter DC DF DG DS DT Flash GP Help NA NM n n Reset SA SB SN ST TH WC WT n nnnn mm nn mm nn uC Volts 3 3 uC TempC 26 6 GPS TempC 235 0 kPa 0 BA Display BA bb b gg g calibrates kPa Baseline Gain See HB CE Enable CD Disable Controls TMC Running bit CPLD CCR1 Display Counters and Control Registers of CPLD address 0 4 Display Scalar Fifo Data first 12 Bytes as three 32bit numbers Display GPS Date Time Position and
36. mparators set a HIGH logic level whenever the amplified PMT signal exceeds their reference voltage setting This logic level has 0 75nsresolution This means we can actually measure the time difference between pulses on different channels at the same site down to less than a nanosecond Of course we depend upon the GPS clocks with 24nsresolution for timing between school sites 2 2 Coincidence logic In the NIM coincidence modules the majority trigger logic is easy to understand For example if we select 2 fold coincidence whenever any 2 inputs which are discriminator output logic signals go HIGH within a fixed time interval 100 ns typically the logic unit outputs a pulse of fixed width typically also 100 ns Ouarknet WALTA CROP Card 11 23 2003 The DAQ card works in a slightly more complicated way This compromise was necessary to implement the performance we need on a low cost board For example if the trigger criterion is set to 2 fold then as soon as any channel goes above threshold a 240 nanosecond wide time window is opened window width is adjustable If any other channel goes above threshold during this time window all event data are latched and output for the overlap time interval when both are active Notice that pulse data are reported for a time interval that is not of fixed length but just covers the overlap period when 2 or more channels are active Leading and trailing edge times are reported for any activ
37. n doing the arithmetic There is a caveat to the previous paragraph if the data rate is very slow less than about one event per 100 sec the internal counter may roll over more than once between readings In this case all bets are off and the seconds cannot be reliably calculated In the next firmware update we will implement commands to produce an output line at each 1PPS and or automatic DG commands at regular intervals ensuring that the necessary information is logged between counter rollovers One minor correction is also needed the GPS module reports the time in down to milliseconds but there is a delay of a fraction of a second relative to the 1PPS edge For example when the IPPS signal tells us it is exactly 12 01 25 000000000 the GPS time field in the data record may say it is 12 01 24 850 This delay reported as 0 150 sec in this example will cause us to associate the wrong integer second with the event time if we are not careful The GPS time delay may be negative i e a forward shift with the ASCII time data ahead of the 1PPS signal The DAQ card is programmed to list the delay in milliseconds for each data record so the reported time in seconds can be corrected to match the 1PPS data The algorithm described below implements these calculations Quarknet WALTA CROP DAQ Card 11 23 2003 Note for people who like really deep down details the delay mentioned above which we can determine and correct is not the whol
38. ncidences are found after first giving scaler contents Each event record may contain several lines of data Appendix A gives a detailed description of the data format and its interpretation Housekeeping and auxiliary sensor data The command TH reports the reading of the temperature sensor on the GPS module connector about 3 feet from the GPS module itseslf The miniature circuit board inside the connector does not generate significant heat so the sensor s reading will provide an accurate measurement of the temperature at the sensor s location e g outdoor air temperature or temperature inside a counter housing The GPS module may be damaged if its temperature goes below 40C or above 85 This temperature is also reported at power up or reset The command BA reports the pressure sensor reading this function has not been fully implemented yet as of 9 03 At DAQ card power up or reset the temperature on the DAQ card actually inside the MCU chip is reported Note that this is not a good indicator of air temperature at the card site even if the card is located outdoors since the chip generates considerable heat while operating It is a useful way to make sure the card is healthy however Temperatures over 40 may be dangerous to the card s chips At power up housekeeping data like the MCU voltage which should be 3 3V and the card s unique serial number which may be needed for upgrades are reported 10 Quarknet
39. ng information could be provided At the SALTA Workshop held as part of the Snowmass 2001 meeting the Quarknet team from Fermilab joined the WALTA and CROP teams to plan an improved Version 2 card The goals were nanosecond local timing lt 100 nanosecond absolute timing report all pulse edge times within a reasonable time window up to 4 fold majority logic total cost under US 500 Remarkably these goals were quickly achieved A team at KEK the Japanese equivalent of Fermilab had developed a time to digital module for the ATLAS particle physics experiment using a custom made ASIC chip called TMC Time Measurement Cell Samples were available at Fermilab and were used in the new board design to provide the detailed precise timing data needed for air shower detectors In addition the TMC chips allowed us to perform TOT estimates for pulse area UW engineer Hans Berns designed and implemented an on board system to integrate data from a very low cost US 100 GPS receiver module providing the final piece of missing functionality The Fermilab team revised the board and its firmware to better encompass the needs of air shower experiments Team members at Seattle and Lincoln worked on user friendly Lab View interfaces for the cards as well as black box software for standard tasks After CROP and WALTA lab tested prototypes production specimens of Version 2 cards were distributed in summer 2003 29 Quarknet W ALTA CROP DAQ Card
40. nput 0 has no falling edge bit5 0 so ignore bits0 4 RE1 00 gt input 1 has no rising edge FE1 01 gt input 1 has no falling edge RE2 38 gt bit5 1 input 2 rising edge bits0 4 0x18 27 FE2 FEA line 2 trigger count REO FEO RE1 FEl RE2 FE2 RE3 line 3 trigger count REO FEO FE1 RE2 FE2 RE3 FE3 line 4 trigger count REO FEO RE1 FEl RE2 FE2 RE3 FE3 line trigger count REO FEO RE1 FE1 RE2 FE2 RE3 FE3 Quarknet W ALTA CROP Card 11 23 2003 24 32 24ns 18 0 ns 01 input 2 has no falling edge 3C gt bit5 1 gt 18 32 24ns 21 0 ns 01 gt input 3 has no falling edge 24 3D 25 01 00 01 00 01 24 gt input 3D gt input 0 input 3 rising edge 0x1C 0x80EE004A 2163081290 decimal 00 ns 75 ns gt 24nsfrom trigger count at event start line 1 rising edge 0x04 gt 3 00 24 27 falling edge 0 1 gt 21 75 24 45 rising edge 0x05 gt 3 75 24 27 25 input 01 input 00 gt input 01 input 00 gt input 01 input WN N bb 3 80EE004B 21 2A inpu 00 gt inpu 01 inpu 00 gt inpu 01 inpu has no falling edge has no rising edge has no falling edge has no rising edge has no falling edge 01 00 23 00 01 00 O1 0x80EE004B 2163081291 decimal
41. oscillator which thus ticks every 24 nanoseconds 1 41 667x10 sec Of course such a device does not maintain its frequency very accurately and our oscillator s frequency may drift by 10 to 100 Hz from its nominal value or more under extreme temperature changes We simply keep a counter scaler counting the clock ticks Whenever this 32 bit counter reaches its maximum capacity of 4 3 billion approximately every 100 seconds it just rolls over back to zero like an old car s odometer and continues counting All we need to do is log the reading of the internal clock counter every time a 1PPS signal arrives Then we know how many oscillator cycles actually occurred during the past second and can calibrate our clock using the GPS system In this way we can take advantage of the US government s multimillion dollar array of atomic clocks that calibrate the GPS system continuously So if we log the counter reading every 1PPS and also whenever a trigger occurs we can find the precise event time as follows get the date and time down to the nearest second from the GPS module s coarse time with one correction described below find the number of clock ticks between the last 1PPS and the event trigger and divide by the number of clock ticks between the last two 1PPS pulses to get the fraction of a second down to 24nsprecision Of course if the counter rolled over during the last second we have to take that into account whe
42. s the raw GPS information to produce the DG command output this will continue to be true even after you send the NM 1 command but you will get many more lines of detailed data in the GPS industry s standard NMEA format see for example http www phys washington edu berns archive Leadtek GPS Protocol ReferenceManual pdt To disable NMEA data forwarding and return to normal operation send the command NM 1 1 Note If you connect the GPS module directly to your PC s serial port via the adapter shown in Fig 2c you can also use a software package provided by LeadTek see http www phys washington edu berns archive Leadtek GMonitor exe to display sky maps of satellites and other interesting data 4 3 Measuring singles and coincidence rates The previous section described how to get total counts of coincidences Of course you could start stop and read the counters using a stopwatch as when using NIM scalers but the GPS clock is a better stopwatch To get rates do the following Do the setup procedures described above up to the CE command 12 Quarknet WALTA CROP DAQ Card 11 23 2003 Get the GPS time and immediately start counting DG CE After an appropriate length of time stop and immediately get the GPS time CD DG Read out the total counts DS Then divide counts by elapsed time difference between times reported in the before and after GPS readings to get rates Of course
43. te overlap time of the individual channel gates so only its leading edge is reported Signal and gate timing input 0 gate 0 TMC delay 0 input 1 gate 1 TMC delay 1 2 fold TRG Edges 0 Edges 1 24 ns time bin Fig A2 pulse timing diagram of example B 23 Quarknet WALTA CROP Card 11 23 2003 Example Signal in channel 1 arrives 5 clock ticks 120 ns after signal in channel 0 Note that the delay value is 6 clock ticks 144 ns So in this case both edges of the signal on channel 1 lie outside the trigger overlap window and are not reported If your physics application involves simply counting triggers as in a muon telescope no problem But if you are analyzing edge time data as in a muon decay or air shower experiment this would appear to be a 1 fold event If this situation represented real physics process you wanted to study you would need to lengthen the values of d and w to accept all the edges in this event Otherwise it will look like a random background event that you have to eliminate or ignore when you analyze the data Homework problem what would happen if we had set w 2d 1 13 instead of 10 Signal and gate timing input O gate 0 Edges 0 Edges 1 17171 Tio Uem 11 Too 1711 12 16 20 24 ns time bin
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