Any idea how to wait for the changing signal to settle over time before measurement?

[astroboy]

Hi. I am going to measure the DC signal in Voltage, using the basic averaged DC-RMS or averaged DC-RMS function.

The problem is that once the system is on, there will be unstable readings like exponential or changing signal till the signal reached at point where there's no change or little changes. Alternatively, I can use the delay function to wait for the signal to settle but the delay time cannot be defined. I am thinking of using the function to monitor for no change or little changes before measurement.

So how do we do that?

Clement

[Henrik_Volkers]

here is one way:

http://forums.ni.com/ni/board/message?board.id=170&message.id=151126#M151126

However that will not work if you have very slow but constant drift. If you don't want to loose time you can use a ring buffer and store the values of your minimum 'stable' time (maybe not all values but min and max during periods). Get the min and max of your buffer and you have a value to work with. I did that (long time before) for temperature calibration and it worked out great. Sorry I can't post that vis, even when I find the buried CD (Final thesis box, basement??) , they are LV4.0

[mycroft]

Shouldn't be to hard.

Just  scan the voltage periodicaly and if the difference between the actual reading and the former one (use a shift register) is within your limit increment a counter. If the difference is above your limit clear the counter.

If the counter reaches -let's say- 3 than you have a stable signal.

Greez

Stefan

Message Edited by mycroft on 11-25-2005 04:30 AM

Message Edited by mycroft on 11-25-2005 04:31 AM

[AndrewAlford]

Here's how I do it, This is part of a large application. You can ignore the index array portion, the instrument I use returns a measurement array. I am only interested in the first measurement the subVI (READHARM) performs the measurement read. I continue to to read the measurement every second and compare it to the last measurement, when the measurements are within +-0.1 of each other the loop stops.

Message Edited by AndrewAlford on 11-25-2005 02:44 PM