AD8497 Amplifier connection to thermocouple

[JLocke]

Hello,

Recently I have been trying to connect my K-type thermocouple to the NI 6009 DAQ. However I noticed that the signal obtained was not pretty accurate so I acquired a AD8497 (http://www.analog.com/static/imported-files/data_sheets/AD8494_8495_8496_8497.pdf)

As you will see in the pictures attached I (think) managed to wire according to the circuit shown in the datasheet. However when trying it with LabView I do not obtain a reasonable value for the temperature, however I got a voltage of approx. 1.38 V which according to the multimeter measurement it is pretty good.

So I am hoping someone can help me with that, since I do not see any other way to obtain temperature measurements from 6009 than the one I am using, and I think everything is correct.

Thanks

JLocke

[moderator1983]

How have you configured the DAQ...?? Is it RSE or differential?? Can you share the VI or only part of code which is responsible for data acquisition.

[JLocke]

I configured RSE.

Here I attach the file. The main aim is to drive a heating tape according to a setpoint temperature. However the temperature measurement has some problem I cannot solve.

Thanks

JLocke

[moderator1983]

I'm not sure which should go to the 'Ground' terminal of USB DAQ... Should it be NEGATIVE SUPPLY or SENSE..!!

are you able to read correct voltage using a digital multimeter, try read the output of AD8497 IC with respect to SENSE terminal.

[JLocke]

well, according to the datasheet, both the SENSE and OUT are wired to the AI channel of the DAQ, therefore I am wiring the reference to the GND of the DAQ as well. I am reading around 1.4 V from that, which to me is WAY too big! That's the problem, since I should expect around 240 mV to get ambient temperature but I do not.

My main concern is about the wiring or the DAQ itself, because I think is not that complicated to integrate the circuit with LabVIEW isn't it?

Thanks

JL

[moderator1983]

I think connection to USB DAQ card should be..!!

[JLocke]

But don't you think I should ground my power supply or so? how about the reference pin?

[jas1991]

I did that as you said and in my case the voltage output now is around 300 mV which is similar to expected, however the temperature is not (using the VI file been attached), are you sure it is not missing anything else?