Temperature conv. subvi

[Tripepperoni]

Hai,

I'm looking for a small answer to the cjc function in the block. I need to use the block which is below, because i got 4 thermocouples and an external gain K=100. The thing is, I don't own any additional sensor but my room temeprature is constant. So my question is, how should I solve the thing with cjc voltage ? My roomtemeprature is ~ 20 degC. I can't find any tables with temperature-voltage values for ic sensor or thermistor ( this one doesn't have a linear characteristics ) 

It's not possible to use one of my thermocouples to do cjc.

Thanks in advance !

[altenbach]

You can open the diagram and see what the code does. Basically, it simply adds the TC voltage of the reference temperature, and since you know the temperature, you can do the same directly. Things won't be very accurate, though.

( you could even use the VI unchanged, wire IC sensor, and wire a CJC voltage constant that results in your temperature going to the fisrst subVI.)

[Tripepperoni]

Do you mean this ? Last time ( today ) I did like in this picture, my block kept changing to Convert Thermocouple Reading ( array ).vi from Convert Thermocouple Reading ( waveform ) and there was a problem in an onverwritten library subvi. ( this block is not working anymore after this change )

[altenbach]

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@Tripepperoni wrote:

... there was a problem in an onverwritten library subvi. 

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Never...ever...overwrite system VIs. The conversion tool is polymorphic, so you need to select the correct code instance.

[Tripepperoni]

I tried to do it your way, sir. I think I succeeded, didn't I ? I need a confirmation. ( I will be able to check if it works not sooner than tomorrow morning )

[altenbach · Accepted solution]

Since you only use the first array element of the waveform, that's all you need to process. So simplify the subVI and eliminate the FOR loop and everything waveform related. Don't process the entire wavform, just to throw almost everything (except the first element) away afterwards.

[altenbach]

So, where exactly is the cold junction? If it is near any electronic device, exposed to light or touch, etc. Your readings can be drifting all over the place. What precision do you need?

[Tripepperoni]

I'm not doing anything that needs to be highly accurate. Fortunately, it's quite far from the sources of heat so it shouldn't make any troubles. My precision should be at around 1-2 deg C, I don't need accuracy to the values after the comma.

[RavensFan]

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@Tripepperoni wrote:

I'm not doing anything that needs to be highly accurate. Fortunately, it's quite far from the sources of heat so it shouldn't make any troubles. My precision should be at around 1-2 deg C, I don't need accuracy to the values after the comma.

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What comma?

[altenbach]

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@RavensFan wrote:

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@Tripepperoni wrote:

I'm not doing anything that needs to be highly accurate. Fortunately, it's quite far from the sources of heat so it shouldn't make any troubles. My precision should be at around 1-2 deg C, I don't need accuracy to the values after the comma.

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What comma?

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comma in certain European countries, decimal point elsewhere. 😄

Also remember that compaines often reduce AC/heating at night to save energy, so the fluctuations could be larger than you think if you look at long-term traces.