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[SOLVED] Thermocouple signal amplification using INA126P

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ponnus

ponnus

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Hai,
I'm trying to interface a thermocouple to microcontroller. As the thermocouple produces very low voltage, I've given an INA126P instrumentation amplifier to amplify the voltage. I'm using +5V as V+ and GND as V- and Vref=2.5V.
But, in the datasheet it says input common mode voltage is 1.5V to 3.5V (from graph). So, I tried to add an offset to the thermocouple input.
I've done that in two ways:1)Using an Op-amp and 2)Using a voltage divider.
here is my schematic........
1)Using voltage divider......
Sathu0737.jpg

2)Using Opamp.....
Sathu0738.jpg

Sorry, it's hand drawn....
May I know my circuit is correct?

Thank you
 

The OP circuit will kill INA126 offset performance. The voltage divider circuit is O.K., except for the 100 nF output load, which won't be accepted by INA126.
 
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    ponnus

    ponnus

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Hai,
Thank you for the reply.
I've replaced the voltage divider with TL431 2.5V reference source and tested the circuit by taking thermocouple readings.
Now, I like to set Vref of INA126 as 1.2V.
Is it ok, if I use a voltage divider or 1.2V zener as Vref?

Thank you
 

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