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Transcript
APD Long Term Gamma Test Description Apparatus There are two identical test PCBs, which each hold 20 APDs. 16 of the APDs on each PCB are arranged in a rectangle in the center of the board, and have the Integrator/Sample/Hold amplifiers supplied by A. Dolgopolov. The other four are outside the rectangle. One of the test boards is in a steel box bolted to the source assembly, which will expose the center 16 APDs to the gamma flux, and the other is in an aluminum box of the same dimensions, which will act as a nonirradiated control. A single 0-500v bias supply for both boxes is controlled through a DAC output on the Agilent 34970A. Each test PCB contains a voltage divider for monitoring the actual bias value. Only the Value from PCB1 is used in the calculations, with the second displayed and recorded mainly as a telltale for problems. We designed a sequencer/interface PCB which accepts TTL signals from the DIO port of the Agilent 34970A for control of the pulser. The sequencer PCB takes care of the timing of the nanosecond Gate/Start/Hold sequence to the Sample/Hold amps (see Figure 1) and the Minsk LED Pulser. Between measurements, a 200hz astable multivibrator to maintain pulser stability continuously triggers this sequence. Temperature of the APDs is maintained within +/-0.1 degC. In each box, a spring loaded aluminum plate is held in thermal contact with the APDs using gap filler. Two 100 ohm platinum resistance thermometers (RTDs) are mounted on each plate, one monitored by the data acq system, the other used as feedback for a proportional (PID) temperature controller. The controllers, one for each box, vary 24VDC power to foil heater elements on the plates as needed to hold the temperature at the setpoint, 35degC. Pulse measurements are taken at a fixed bias voltage by the Labview application on a time interval in seconds. While either the red or blue LED can be used, red is being used due to its higher output. When a pulse measurement needs to be made, the astable is stopped, and the last held values are immediately read from pin 6 OUT of the sample/hold amps by the 34970a using a low resolution, fast scan. All 32 pulse channels are read in about 1 sec. Bias and temp readings are also taken after the pulse channels. The DC gain and breakdown measurements are taken on a longer time interval, and include four additional APDs (117-120, 217-220) on each circuit board, which have no pulse amplifiers, but identical series resistances. This measurement sequence takes about 20 minutes to complete, since the high resolution (10 power line cycle integration) scan must be used to obtain the gain curves. Again, the astable LED trigger is stopped during this procedure. For each supply bias value, current is calculated from the voltage drop across the 10kohm resistor in the anode leg of each APD, and then the individual biases are factored from the supply value using the known values of the series resistors. First the dark current curves are measured, then the Constant (blue only) LED output is turned on, and the total current curves are measured. Then Vr and Id are calculated for gain 50. Immediately after the DC Gain measurements are finished, the bias is ramped up to a value above breakdown for all APDs and the zener breakdown voltage is read using a fast scan. The series resistors in each APD circuit limit the breakdown currents. Again, actual APD voltage is factored from the common supply voltage using APD current and the known series resistances. The entire Breakdown step takes about 5 seconds, after which the APD bias is ramped back down and astable pulsing is resumed until the next measurement. Figure 1 LTgamma input circuit (1 of 32) showing APD and Integrator/Sample/Hold Amplifier Data Description Four data files are created and written to during operation of the tester. One file is maintained for the calculated results of each of the Pulse, Vr, and Breakdown tests, with a new line appended for each repeat. An additional file for the raw data used in each Vr test is kept with a more complicated structure consisting of a multi-line table of data per repeat test. All files are tab delimited ASCII, with two header lines. The top line contains instrument settings and the second line contains column headers for the data. APD numbering convention is: 1xx=non-irradiated, 2xx=irradiated. New data files are opened each time the Labview program is started. Filenames have the date/time of the start of execution embedded. Truncated examples of all four files have been imported into an Excel workbook file, LTGamma_Datafile_Examples.xls, imported as text so the data appears exactly as written to the files. Pulse Response Data File Pulse response data is written to the yymmdd_hhmm_Pulse_Tests.txt file. The top line headers document voltmeter range, integration time, and the number of repeat measurements being taken and averaged. At this writing, the range and integration headers say “Gain xxx” and actually indicate the integer value of an enumerated type control where the string selections should have been**. The decoded selections are: Range (full scale): 0=100mV, 1=1V, 2=10V, 3=100V, 4=300V Integration time (number of power line cycles): 0=0.02NPLC, 1=0.2NPLC, 2=1NPLC, 3=2NPLC, 4=10NPLC, 5=20NPLC Column headers form the second header line. They are as follows with a description of column data: Date/Time Timestamp in mm/dd/yyyy hh:mm:ss format Bias1 Bias volts from divider on non-irradiated PCB Bias2 Bias “ “ “ irradiated PCB PCB1 degC RTD temp on heater plate non-irradiated PCB PCB2 degC RTD temp “ “ “ irradiated PCB Amb degC Type J TC in air near 19” rack APD101 Sample/Hold volts from amplifier on APD101 ………. APD216 Sample/Hold volts from amplifier on APD216 DC Gain Data File Data calculated from the total current and dark current curves are written to the yymmdd_hhmm_DC_Gain_.txt file. The first line headers document voltmeter range, integration time, voltmeter impedance, and number of averaged repeats (in plain English). Impedance is unfortunately labeled #Scan/step**. Second line column headers and data descriptions follow: Date/Time Timestamp in mm/dd/yyyy hh:mm:ss format PCB1 degC RTD temp on heater plate non-irradiated PCB PCB2 degC RTD temp “ “ “ irradiated PCB Amb degC Type J TC in air near 19” rack Vr101 Gain=50 operating voltage for APD101 ……… Vr220 Gain=50 operating voltage for APD220 Id(uA)101 Gain=50 dark current for APD101 ……… Id(uA)220 Gain50 dark current for APD220 M1uA101 Calculated gain=1 photocurrent in microamps for APD101 ………. M1uA220 Calculated gain=1 photocurrent in microamps for APD220 M1StDev101 Standard deviation of Gain=1 calculation APD101 ………. M1StDev220 Standard deviation of Gain=1 calculation APD220 ** These mistakes(mine, -BG) caused by copying and pasting Labview front panel controls and forgetting to set new values as defaults. DC Raw Data File Raw data used in Gain 50 Vr calculations is saved in the yymmdd_hhmm_DC_Raw.txt file. The first line headers document voltmeter range, integration time, voltmeter impedance, and number of averaged repeats. Each time the Vr test is run, a single time stamp is written alone on a line followed by a line of data for each bias step, first for the dark current curve, then the total current curve. Second line column headers and data descriptions follow: Date/Time PCB1 Bias PCB2 Bias PCB1 degC PCB2 degC Amb degC Bias101 ….. Bias220 uA101 ……. uA220 Timestamp in mm/dd/yyyy hh:mm:ss format Bias volts from divider on non-irradiated PCB Bias “ “ “ irradiated PCB RTD temp on heater plate non-irradiated PCB RTD temp “ “ “ irradiated PCB Type J TC in air near 19” rack Actual APD101 bias factored from current and resistance Actual APD220 bias factored from current and resistance APD101 current in microamps at this step APD220 current in microamps at this step DC Breakdown Voltage, Vb Data from the breakdown test is written to the yymmdd_hhmm_DC_Brkdn_.txt file. The first line headers document voltmeter range, integration time, voltmeter impedance, and number of averaged repeats. The second line headers are as follows: Date/Time PCB1 Bias PCB2 Bias PCB1 degC PCB2 degC Amb degC Vb101 ………. Vb220 uA101 ………. uA220 Timestamp in mm/dd/yyyy hh:mm:ss format Bias volts from divider on non-irradiated PCB Bias “ “ “ irradiated PCB RTD temp on heater plate non-irradiated PCB RTD temp “ “ “ irradiated PCB Type J TC in air near 19” rack APD101 calculated breakdown voltage APD220 calculated breakdown voltage APD101 breakdown current, microamps APD220 breakdown current, microamps