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CFD Testing How To

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CFD Testing HowTo by Thomas Roche I. Introduction II. Setup III. Mode IV. DAClinearity (A and B) V. RFB Calibration VI. Width VII. Threshold VIII. Noise Calibration IX. Rate Feed Back X. Timing XI. Database Connection XII. Appendix I I. Introduction The following HowTo will instruct the reader in testing Cross Fractional Discriminators for use with the VERITAS telescope array. This is not meant to be an exhaustive explanation of the testing procedure but a more direct, step by step approach. For a more detailed explanation please consult the manual. There are nine (9) tests to be performed for each CFD. They vary in length from a few minutes to over 10 hours. Some of the tests require the use of LabView. The DAClinearity, RFBlinearity and DACBthreshold tests are run solely from the command line. All of the tests should be run in the order presented here. II. Setup The testing area consists of 1 computer, 1 oscilloscope, (some amount) of signal generators, 1 linear fan out and 15 test rigs. Everything is controlled by the computer via serial and GPIB communications. LabView LabView is used for most of the data gathering. The executable is: /usr/local/lv70/labview All of the test programs or “Vi s” are located in: /usr/local/lv70/user.lib/ Auxiliary Programs In addition to the LabView programs there are a collection of programs that deal with data analysis and database interaction. The binaries are located in: /home/cfduser/CFDdata/bin/ This path is included in the $PATH environment variable so you don't need to type the full path when using them. III. Mode Test This is a simple test that tests all of the functions of the CFD very quickly. Follow these steps: 1. Connect standard signal generator as described in appendix 1 to CFD and scope. 2. Connect Input from CFD to scope as described in appendix 1. 3. Open CFD.vi LabView program. 4. Select proper VISA device. 5. Set DACA = 4095, DACB = 1450, Mode = Threshold, POT = 0. 6. Read Voltages: Width should ~ 1.27V, Threshold ~ ‐50mV, RFB ~ ‐3 mV 7. Read Scope Output: Should see signal and it should be about 28 ns wide. 8. Set DACA = 0, DACB = 1550, others same. 9. Read Voltages: Width ~ ‐0.57, Threshold ~ ‐100mV 10. On the Scope the position of the output pulse should shift to the right by ~ 4 ns 11. Set DACB = 0, Mode = CFD. 12. Run VI and watch output. Output should disappear then turn into noise when the CFD mode is activated. 13. Check Threshold voltage should read ~ 1356mV 14. Set DACB = 1450. 15. Set POT = 127. 16. Turn off all SET options and tell the VI to Run Continuously. 17. You should see an immediate drop in RFB ~ ‐3V which will quickly increase to ~ ‐50mV. 18. Set DACB = 4095. 19. Threshold voltage should read ~ ‐2630mV. 20. Next run the program in a terminal “modetest” and follow the instructions. IV. DAClinearity (A and B) This test will verify that the digital to analog converters on the CFD are functioning correctly. A is responsible for the width and B is responsible for the threshold. There are 4096 settings for each DAC. The test takes a little longer than 10 hours to run. This is why there are 15 test rigs. This program does NOT use LabView. I found a simple c program was more efficient. It is called DAClinearity. If you type that at the prompt you will be given the following: [[email protected] troche]$ DAClinearity_test usage: DAClinearity_test [‐l <lLimit> ‐u <uLimit> ‐s <step> ‐n <samples>] ‐p <port> ‐i <CFDid> ‐l <lLimit> Lower DAC limit ‐u <uLimit> Upper DAC limit ‐s <step> Step between DAC values ‐n <samples> Number of Samples at each DAC value ‐p <port> Serial port to use [MOXA channel 1‐15] integer 1‐15 ‐i <CFDid> ID of the CFD being tested [[email protected] troche]$ Generally you will only need to set the port and CFDid. To run the test do the following: 1. Run the program with at least ‐i and ‐p switches given. 2. Wait for it to finish (~ 10 hours). Caution: Do not open a new session of lab view while running this program. It will reset the serial ports and disrupt the test. 3. Run the “insert” program to put the data into the database. 4. Next run the “linear_test” program. Give it the CFDid of the data you have inserted in the previous step and it will fit lines to the data and determine the chi squared. 5. If chi‐squared for both lines are less than one (<1) then the DACs are behaving normally. V. Width test This test will measure the actual width of the output pulse of the CFD. Since you must use the scope for this test it is only possible to do one at a time. The procedure takes about 16 minutes to complete. Follow these steps: 1. Open LabView program “DACAwidth.vi” 2. Set the Horizontal Position of the trigger on the scope to 5% or less. 3. Connect signal generator as described in Appendix 1. 4. Connect output of CFD to scope channel 1. 5. You may need to adjust the delay between chan nels A and C depending on your cable length. 6. Input the 4 digit CFDid in the appropriate place and run the program. 7. Insert the data into the database with “insert”. VI. RFB Calibration This test will measure the DC offset that results from adjusting the potentiometer in the rate feed back circuit with a controlled pulse. The test takes about 15 minutes. You may run 14 tests at a time ( The test rig that is specially designed for noise calibration should not be used for this test ). 1. Set up the pulse generator to deliver a 1 volt pulse at 1 MHz. Use the linear fan out to connect it to the desired number of test rigs. There is a gain of ~5 from the input on the CFD test board to the input to the CFD itself so adjust the pulse accordingly. The settings saved in slot 1 on the signal generator will produce the best possible pulse shape. Connect two 10 dB attenuators directly to the output of the signal generator. 2. Use the c program RFBlinearity. This program has an interface just like that of DAClinearity. You need only input the CFDid and MOXA number as before. 4. Insert the data into the database with “insert”. 5. Now the tests necessary to calculate the coefficient s for run time programming have been completed. Run the program “coeff” with the CFDid as the first argument for each CFD that has been tested up to this point. 6. Run the program “plot_dac” with a CFDid as the argument to make sure the lines fit the data. The data gathered so far is sufficient for run time operation. The rest of the


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