Temperature Stabilization Detection Not Working Correctly

[abrandenfels]

I am trying to write a program that detects when the temperature from a thermocouple (on channel 6) has stabilized, and starts recording the data to file when this occurs.

The criteria for stabilization is such that if the difference between the temperature at a given time and the temperature at x (adjustable value) seconds earlier is less than a specified threshold value, then it is stabilized.

I wrote a while loop that waits x seconds and uses shift registers to compare values between iterations of the loop. Ideally, the program would get the temperature for t=0, wait x seconds, and compare the temperature values for t=0 and t=x. However, the input from the DAC assistant appears to get "backed up" during the wait, and on the second iteration, it compares t=0 with t=1. I would like to know how to remove values from t=1 to t=x-1 from the data stream. Please let me know if you have a solution.

[RTSLVU]

Well we use a different standard for stabilization here per UL1778 Section 49 "Temperature change shall be less than 2 degrees C over 3 consecutive 15 minute intervals" and I created an "action engine" to test for it.

You feed it a numeric array containing your measurements every 15 minutes to test for stabilization

You might have to change the High and Low limits depending on your application in the "Write" state.

I use this in a program for thermal testing power transformers and use redings outside of 0C and 200C as open thermocouple detection.

[BertMcMahan]

I ran across this post the other day, it sounds like it could help you out:

https://forums.ni.com/t5/LabVIEW/A-should-be-simple-DAQmx-question-take-finite-samples-in/m-p/361991...

(BTW, in general it's fairly poor practice to use the DAQ Assistant in "real" programs- you'll be much better off in the long term to understand the underlying DAQmx functions.)

[RavensFan]

What wait are you putting into the wait function in the loop?

You set your DAQ Assistant to read 1 sample at a time at 1 Hz.  If you wait any longer than 1 second with that wait function, the samples will be coming in faster than you are reading them since you are reading them only one at a time.

Instead of Continuous samples, try N samples.  But better yet is to use one of the examples provided above.