[SOLVED] INA126: getting unexpected results

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I just obtained the thermocouple from the lab and it has two leads (red, black) with a shield. I connected the shield to the circuit ground.
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In other words, the thermocouple circuit itself is floating. This would pretty explain failure in operation.
 

sure now on with it tell me your reading fron an..output.
plsase tc in boiling water water and post reading then in ice and post reading from an..output
 

Connected a 10k between pin 3 and ground (should I connect it between thermocouple V+ and ground?). I measured the output voltage at pin 6 and it was 4.3V. But my reference voltage to AD converter is 4.096V. It seems INA126 is saturated. It doesn't change though I reduce the gain (using 1k var resistor). How can I identify what to do?

Is it something to do with common mode voltage?
 
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    ptkien

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The 10 k resistor should be sufficient to cancel input floating. From your description, I don't see an explanation for amplifier saturation. It may be a wiring fault or defective chip. You should measure the voltage level at all INA126 pins against ground to narrow down the problem.
 
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    ptkien

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What is your supply voltages -v...+v in ref to grd ?
the 10k resistor is for -v=zero.
 

I assembled INA126 circuit separately and measured the output. It works perfectly and I get the output according to the gain. But when I connected it to PIC circuit, output fluctuates. What can be the reason? I am having problems with the power supply design as well.

I have a power supply of 0-18V. How can I design the power supply so that it will have a common ground for PIC and INA126 (this needs V-0-V)?

INA126 may have to be supplied 6-0-6 since I have used 4.096v as the reference voltage for PIC (for AD conversion)
 

Thanks to all of you I finally got through it. There was a problem in the power supply unit. I had to build **broken link removed** PSU since my PSU didn't output a balanced voltage. I guess it was the problem.

Thank you all for your valuable input. (Y)
 

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