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I need Type C thermocouple signal conditioning, or a VI that has the reference table employed.


Has anyone worked with type C t/c's?
Message 1 of 12
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I'm working on it, and I'll have the VIs shortly.

Mark
Message 2 of 12
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Mark,
What an amazing surprise! You are a Prince!
-Tom
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Message 3 of 12
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I've found the C type thermocouple characteristics, and I've incorporated them into the standard "Convert Thermocouple to Temperature VI" that comes with LabVIEW. I'm including it here. It assumes that you're using NI hardware for the CJC; if not, in the diagram you'll see where the CJC temperature is converted to thermocouple voltage and then added to the TC voltage. Simple add your CJC voltage to the TC voltage directly instead of doing the first conversion.

Mark
Message 4 of 12
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Beautiful, Mark. This should help others using NI equipment to measure those ultra high temps! Thank you so much!
-Tom
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Message 5 of 12
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I've simulated voltages to make sure this works, but I'd be interested in your comments when you get it going! Thanks.

Mark
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Message 6 of 12
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I am having trouble with the polynomial that you made. When I am going from Voltage to temperature I am getting a very off value. On the other hand when I go from temperature to voltage I get an accurate answer. I was wondering if you could help me correct this problem. Also where did you come up with these equations, and is there any way I can make them more accurate. Thanks.
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Message 9 of 12
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By the way, if you're interested, the millivolt to deg C table that I used to generate the best-fit polynomial for type C thermocouples is

http://www.shelbyjones.com/OnlineCatalog/Temperature/Sensors/Thermocouples/Thermocouples_Literature/emfc_c_1.htm

The website also has tables for other thermocouple types as well as RTDs. To incorporate this into the VI, you'll have to enter the table values into two separate arrays (X and Y), and then feed that into a best fit polynomial VI to get a curve that best fits those points. You can then add that to the temp to volts VI and volts to temp VI to add the thermocouple.

Of course, only if you're interested. 😉

Mark
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Message 7 of 12
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Thanks for the VI, it is helping me alot. The thing is while I am tring to test it with ceartin voltage values I am not getting the corresponding output based on the website you mentioned. For the VI you modified, this is what I did.

Temperature Setting- degree C
IC Sensor
CJC-0
Voltage Reference
Thermo type- C

I put a test voltage of 13.65mV and get a reading of 563.01 degrees C If you could take a look at my program it would be great.

This is my first time using LabVIEW and I am working as an undergraduate student, so it might not be all that great. Thanks.

There are other stuff going on there which are test cases, so dont have to worry about it.
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Message 8 of 12
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I don't expect any of the orginal posters to respond to this, but for others who found this by searching the discussion board...

I had a look at markwysong's VIs (since I also need to convert Type C thermocouple voltages to temperatures) - they don't work very well.  The general idea is correct, but above 200degC the values are way off (maybe correct values weren't intended).

Anyway, I think that the polynomial coefficients given (extracted from 2nd and 3rd order polynomial fits) just aren't adequate.  Here's what you need to do (step-by-step). 

1. Find type C thermocouple voltage-temperature data (I used one from Omega http://www.omega.com/temperature/Z/zsection.asp - under 'thermocouple reference data').  Incidentally, this website gives Type C coefficients, but for temperature to voltage conversion.  Voltage-temperature conversion coefficients are different (something I didn't realise for a while - d'oh)!  It's the inverse polynomial coefficents that we want (which aren't given for Type C) - see note under point 2.  

2. Using the General Polynomial Fit VI, generate coefficients for whatever order polynomial you want.  I input data for the temperature range 0-1400degC (in 50 degree intervals) and got the following coefficients from a 6th order polynomial fit (can't remember which algorithm, but it doesn't seem to make much difference):

6   -0.0000043837094235

5   +0.00039799817557

4   -0.014640523567

3  +0.2973265406

2   -3.4901476382

1  +73.15121202

0   +0.00036607033979     

These coefficients reproduce the table's data much more accurately, and allow conversions from voltage to temperature.  Note that the temperature data must be wired to 'x values' and voltages to 'y values' in this case.  Wiring oppositely will give coefficients for temperature to voltage conversion.

Hope this helps some fellow Type C-er! Smiley Happy

 

Message 10 of 12
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