Help with measuring temperature VI using Type T thermocouple

[djb4]

I have 2 circuits on a solderless breadboard. Channel AI-1 goes to an AD590 circuit that serves as a cold junction. Channel AI-0 uses a gain circuit that has a type T thermocouple to measure surface temperature.

Basically, the VI needs to add the mV of both circuits together to get the temperature of the thermocouple (surface temperature) to account for the board temperature? My VI does not display the correct temperature in celcius.

Any help is appreciated.

[X.]

Your VI doesn't do what you say it is doing. Your first formula node outputs a "DC" value which is never defined anywhere in it, so the output is zero. Same thing for the second formula node, with the same result. BTW, you don't even use the inputs Ein in either node... Your third node does make something that makes sense : it uses the input to compute an intermediate variable (V) from which is compute a second variable DC, which is finally used as an output.

As a note, you are not using the constants Di defined in the first two nodes, so their purpose is unclear (unless you stripped down your VI before posting it).

[djb4]

This is my VI updated from what it was. I corrected some things in the formula nodes but something in the nodes still isn't correct? It still won't display the correct termperature.

[X.]

Now the formula nodes make sense (but you don't need to introduce the intermediate variable V in them).

Did you put probes before and after each node, step through your diagram and figure out where things go wrong?

[djb4]

I'm not sure what you mean by that.

I placed indicators before/after the nodes just now.

Before formula node 1, I get a value of .52

Between node 1 and node 2 I get a value of 245

After node 2 I get a value of 2879 and between the x1000 and addition functions I get a value of .52.

The final temperature output should just be the value of whatever the type T thermocouple is touching which is just air at the moment and it holds at about 3.778 C which is not room temperature here which is about 16C. It is a spiking around this value and stays around this value regardless of what the TC is touching.

[X.]

Oh my! Check Help>>LabVIEW Help...>>debugging, creating probes

Are you saying the math is sensible? Then the input data are not what you are expecting?

I see that you have a 2D array as an input. What are its typical dimensions? 2xN or Nx2? You may have to invert the indexing scheme you are using right now, by wiring a 0 to the first index as depicted here:

[djb4]

Sorry, I am a beginner Labview user. None of this makes sense to me. The first array should be the voltage of the channel AI 0 gain circuit (TC circuit) which corresponds to a T after going into the node 3. The 2nd array is the channel 1 circuit which accounts for the temperature/voltage of the board and subtracts that front the TC voltage to get a more accurate temperature.

I wired a 0 to the first array like what you did and it is still doing the same thing

[X.]

Can you paste an indicator at the output of your DAQ task (I mean create an indicator by right-clicking on the 2D array output wire), run the VI once, stop it, save all values as default (Edit >> Make Current Values Default), then Save your VI and post it back? Then we can figure out what kind of data you are actually getting from your sensors.