DC Measurements on the A-Card Rev. 31-DEC-1997 The second array has a zero photon output voltage of about 3.5 Volts instead of the planned on 3.1 Volts. Can all of this be taken up by the offset trim in the 3rd stage Op-Amp ? Some measurements. Recall that Test Point #4 is at the ADC input, i.e. after the x0.9 attenuator at the input to the ADC. With just the 1st quadrant modified and with the 1st quadrant set so that all of its zero photon signal could be seen in the displays make some measurements. These measurements are of the V-Clamp signal. V-Clamp = 2.500 Volts Test Point J1 J2 J3 J4 ----- ------- ------- ------- ------- 1 2.497 2.497 2.498 2.497 Volts 2 .819 .769 .763 .772 3 1.018 .958 .949 .961 4 .261 -1.078 -1.066 -1.080 6 1.384 0 0 0 Now modify all 4 A-Cards so that the wiper of the 3rd stage offset pot can pull up to +1.5 Volts. With V-Clamp = 2.500 Volts Test Point J1 J2 J3 J4 ----- ------- ------- ------- ------- 1 2.497 2.496 2.497 2.496 Volts 2 .819 .769 .763 .772 3 1.018 .958 .949 .961 4 -1.142 -1.077 -1.064 -1.079 6 0 0 0 0 +6V Vcc 5.88 5.98 5.98 5.98 Now set V-Clamp = 3.500 Volts an re-measure. Test Point J1 J2 J3 J4 ----- ------- ------- ------- ------- 1 3.499 3.499 3.500 3.499 Volts 2 2.358 2.308 2.305 2.310 3 2.935 2.875 2.871 2.880 4 -3.289 -3.229 -3.215 -3.232 6 0 0 0 0 Now adjust the 3rd Stage offset to get a test point #4 voltage of about -2.15 Volts. Keep the V-Clamp at 3.500 Volts. NOTE THAT THIS IS AN ERROR. The 3rd State offset should have been adjusted to give a Test Point #4 Voltage of something like -1.950 Volts because Test Point #4 is actuall the input to the ADC not the 3rd Stage Output. Test Point J1 J2 J3 J4 ----- ------- ------- ------- ------- 1 3.499 3.499 3.500 3.499 Volts 2 2.358 2.308 2.305 2.310 3 2.935 2.875 2.871 2.880 4 -2.149 -2.150 -2.150 -2.150 6 1.126 1.067 1.049 1.065 Now adjust the V-Clamp Supply to 2.500 Volts Test Point J1 J2 J3 J4 ----- ------- ------- ------- ------- 1 2.496 2.495 2.496 2.495 Volts 4 +0.002 +0.008 +0.005 +0.008 This is how it was shipped on 30-DEC-1997. Recall the Analog Processor designed gain and offset chain: First Second Third OpAmp OpAmp OpAmp Input Photon TCM2620 Output Output Output to the Signal Output (+6 V Ref) (0 V Ref) (+39 mV Ref) ADS-946 ------ ------- ---------- --------- ------------ ------- Max. +1.3 V -1.351 V -1.688 V +2.2 V +2.0 V Mid. +2.2 V +0.057 V +0.071 V 0 V 0.0 V Zero +3.1 V +1.464 V +1.831 V -2.2 V -2.0 V SPAN 1.8 V 2.816 V 3.520 V 4.4 V 4.0 V ---- Required <-- +1.564 --><-- +1.250 --><-- -1.250 --><-- +0.909 --> Signal Gain <------------- - 2.444 ---------------> -------- Resulting Reference <-- -0.564 --> <-- +2.250 --> Gain -------- And now look at what 3.500 Volt zero photon signal should do: First Second Third OpAmp OpAmp OpAmp Input Photon TCM2620 Output Output Output to the Signal Output (+6 V Ref) (0 V Ref) (+1.066 Ref) ADS-946 ------ ------- ---------- --------- ------------ ------- Zero +3.5 V +2.090 V +2.612 V -2.2 V -2.0 V Required <-- +1.564 --><-- +1.250 --><-- -1.250 --><-- +0.909 --> Signal Gain <------------- - 2.444 ---------------> -------- Resulting Reference <-- -0.564 --> <-- +2.250 --> Gain -------- With the actual resistors used the gains should actually be First Second Third OpAmp OpAmp OpAmp Input Photon TCM2620 Output Output Output to the Signal Output (+6 V Ref) (0 V Ref) (+1.066 Ref) ADS-946 ------ ------- ---------- --------- ------------ ------- Required <- +1.561 AC-><-- +1.248 --><-- -1.241 --><-- +0.909 --> Signal +1.537 DC Gain -------- Resulting Reference <-- -0.537 --> <-- +2.250 --> Gain -------- |+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+ Measures values on the C130 on Friday 9-JAN-1998 after the zero photon signals had been trimmed. VClamp set to 2.498 Volts. Test Point J1 J2 J3 J4 ----- ------- ------- ------- ------- 1 2.495 2.494 2.497 2.496 Volts ! Array Output 2 0.816 0.766 0.762 0.771 ! 1st Stage Output 3 1.015 0.953 0.948 0.960 ! 2nd Stage Output 4 0.259 0.234 0.387 0.331 ! 3rd Out, ADC In 5 3.750 2.498 5.01 5.00 ! Aux Array Supply 6 1.378 1.289 1.426 1.385 ! 3rd Stage Offset |+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+|+ Measures values on the C130 on Friday 6-FEB-1998 after changing to a +6.5V first stage supply J1 J2 J3 J4 ----- ------- ------- ------- ------- 6.34 6.46 6.43 6.46 Volts ! 1st Stage Vcc Supply & Ref.