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Topic: AD8495 Doesn't Respond to Thermocouple Inputs? (Read 97 times) previous topic - next topic

TLAS

Hello Everyone,

I'm having some problems with an AD8495 thermocouple to analog sensor with an Atmega32U4.

I've seen the sensor work at least once and read a good analog voltage output from a multimeter, so I don't think it's the PCB circuit.  I've double-checked the inputs from the thermocouple sensor a number of times and the inputs always look good (indicating that there isn't a problem on the TC side).  The output seems to be 'stuck' at ~92 mV output, although this does fluctuate if I touch the thermocouple directly and induce 60 Hz noize.  It does not seem to change with temperature or mV changes on the TC side.

I have this directly wired to pin 39 (ADC4) on the microcontroller and use a timer sampling sequence.

Is there something I need to be aware of on the microcontroller side that could be fighting the analog input voltage?  Any other ideas to check?  Could an ESD event cause these problems through the thermocouple wires?  Each line runs though an inductor and I have a cap between each line. On this particular card, I don't have the caps to ground on each line to eliminate additional noise - not too worried about a noisy signal at the moment.


Any thoughts or additional debugging recommendations would be appreciated.


WattsThat

Did you troubleshoot thermocouple/amplifier using the ambient temperature sensor that outputs 5mv/degree C? It's documented on page 14 of the datasheet.
Vacuum tube guy in a solid state world

jremington

#2
Mar 12, 2019, 04:12 am Last Edit: Mar 12, 2019, 04:13 am by jremington
It sounds like you have a ground problem. Please post a complete schematic wiring diagram (hand drawn, not Fritzing).

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