stabilization of measurement

[drsisco]

Hello all,

I am trained to measure the temperature of a thermocouple with a labview program but the measurement result is not stable (see graph attached). If you know a way to get a stable value please help me. The labview program is avaible as an attachment (appointed Thermocouple).

Best regards

[Bob_Schor]

It would be nice to have some idea of the time and amplitude scaling.  Are we looking at "noise", a "bad instrument", or what?  The measurement seems stable enough, just has a lot of variation.  Maybe the physical situation you are measuring has the same variation ...  Or maybe the code you are using is inserting "random noise" into the data.  

Bob Schor

[drsisco]

Bob Schor, thank you for your reply.

The time scaling is: 0 to 500s

amplitude scaling is: 0 to 100°C

The thermocouple works well because i tested it with a multimeter. I believe it is noise that destabilizes the signal and i don't know how to solve this destabilization problem.

Thank you in advance 

[billko]

Over 8-plus minutes, I would start thinking that this is real data, and the issue lies with keeping the temperature stable.

[RTSLVU]

From the look of your Vi you are taking data as fast as possible.

What is your hardware?

Does it have proper cold junction compensation? 

Also I took a quick look and your data it's hard to tell but it looks like it is within the standard accuracy of a thermocouple, as most common types are +/- 2 degrees C.

[drsisco]

billko, 

Yes the problem is with the temperature stability. Is it possible to have a stable value with a labview program ?

[drsisco]

RTSLVU,

This is the type k thermocouple.

I am using the NI-DAQ 6001 available as an attachment.

[RTSLVU]

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@drsisco wrote:

I am using the NI-DAQ 6001 available as an attachment.

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Well there's your problem, no cold junction compensation and a low resolution DAQ.

Best you can do is some type of smoothing like a "running average" of your readings.

[AnalogKid2DigitalMan]

In addition to what RTSLVU stated-

It appears that you are not using K-Type T/C wire- this will cause measurement errors.

-AK2DM

[RTSLVU]

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@AnalogKid2DigitalMan wrote:

In addition to what RTSLVU stated-

It appears that you are not using K-Type T/C wire- this will cause measurement errors.

-AK2DM

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I said that too but when I looked for a table to post I noticed the IEC color code is Green with Green/White wire for K type