A17.2 LAN Spare - LEMS/LEFS LINEAR Offset vs. Temperature

A thermal test of the LEMS/LEFS LINEAR board (SN003) was performed in air over the temperature range -25°C to +55°C. All linear channel outputs were monitored during the test for signs of gain change, intermittents, etc. Specifically, the D.C. offset of signals B, F2, M2, F2', and M2' was measured, and the results are plotted in Figure A17-6. Obviously, the variation is significant, and arises due to the fact that the final amplifier in each energy channel is D.C. coupled to the output. The curves in Figure A17-6 are therefore characteristic of the EME 0529 hybrids used for this stage. (Since this stage provides a gain of 25, a change in the input offset of 1 mV results in a change of 25 mV at the output.)

Figure A17-6 DC offset vs. temperature

The problem could be eliminated by AC coupling, but this would in turn introduce a new problem due to the required configuration of the discriminators which follow, and a rate-dependent offset would ensue. Since the temperature is likely to be more stable than the rates of incoming particles, it was decided to simply monitor board temperature so that the offsets could be inferred and used to correct the apparent threshold of the corresponding discriminators. To this end, one of the spacecraft thermistors (S/C Therm 1) has been moved from its previous location on the Motherboard to a new location on the LEMS/LEFS board as shown in Figure A17-7. U4 is the final stage of channel B. The temperature of the other output stages should track U4 closely.

Figure A17-7 Relocation of S/C Therm 1 on LEMS/LEFS LINEAR board

Next: A17.3 LAN Spare - LEMS/LEFS LINEAR, Crosstalk in Linear Energy Channels

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