PXIe-4080 DMM, Acquisition rate too fast

[arraf196]

Hi guys, so I'm trying to make an continuous Data Acquisition application using the PXIe-4080 DMM that saves the data to a text file. The experiments I'll be doing might last anywhere between 5 mins to upto 5 hours. I am having trouble adjusting the rate at which the fulti-fetch VI's take readings (they are way too fast). I have tried putting a delay timer in the while loop, time delay express vi and stall data lines, all these have the same effect, they destroy the functionality of the program. I've included a screenshot. The VI that i"m trying to slow down is ni-DMM Fetch Multi-Point, all the fixes I tried makes the VI not update (stops reading) anymore.

[Gregory]

Try adding this configuration VI before your while loop, set the interval to what you need:

[arraf196]

This is the main problem, if you read the help description of the " Configure VI " you'll notice it says that the sample interval is ignored by the PXIe 4080. I tried using it and it doesn't make a difference. That is why I'm searching for an alternative.

[Gregory]

Wow, I'm sorry for overlooking that! In that case, I would recommend configuring for waveform acquisition. You can take the mean if you just want the average DC value of the waveform.

[arraf196]

Hey gregory, sorry for the late replay, but with the waveform acquisition I can only read voltage and current. Whereas I'm also trying to read information like inductance, capacitance, temperature from thermocouples, resistance, etc.

[Gregory · Accepted solution]

In that case, I would just let it acquire quickly and downsample after you retrieve the data. You could replace every 1000 points with the mean of those points to downsample by a factor a 1000. The VI attached could weight the last couple points very heavily, but it does not throw anything away.

[arraf196]

Thank you so much! I'll try integrating this into my application and get back in a bit.

[mikethemartian]

I have a related question while doing the same multipoint resistance reading using a PXIe-4080. Even if the user can't set the sample rate can they at least query it ahead of time to dynamically set the number of readings they need to fill a desired length time window? The specifications for the PXIe-4080 states that the Maximum Reading Rate for resistance mode measurements is 20 kS/s but this assumes a minimum aperture time, that Auto Zero, Offset Compensated Ohms and ADC Calibration are all off, the Number of Averages is 1 and Settle Time is 0 seconds. There is a subvi "niDMM Get Aperture Time Info.vi" that will return the aperture time but (even if all the other settings are as above) it is not certain how exactly this converts to the time between samples. The niDMM property node does allow the user to set it to Sampling Interval if connected to the instrument handle out of the "niDMM Configure Multi Point.vi" subvi but this is probably only passing the inputted value which is invalid for the PXIe-4080.