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Message ID: 1818     Entry time: Wed Feb 22 17:21:36 2017
Author: yinzi 
Type: DailyProgress 
Category: TempCtrl 
Subject: troubleshooting temp sensor reading 

The temperature sensor reading is being railed to the negative power voltage whenever a new input command is entered:

The first ramp is at the output of the instrumentation amplifier AD620, the second ramp is at the output of the low-pass filter Andrew put in recently. Also, I looked at the signal going into the AD620 and it did not exhibit this drop, so the problem comes from the AD620 circuit. I tracked the current being drawn on the display of the power supply, and never saw it go above 250mA, but I'm thinking if it's a current problem (overdrawing), it could be happening fast enough to not register on the power supply.

I plan on using a resistor and the oscilloscope to track the power current more closely while I change the input command to see if it is the problem.

Note: if the leads on the temperature sensing circuit are flipped such that the signal is negative, the signal rails to the positive supply voltage whenever an input command is entered.

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