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Mulitple DMM Measurements

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Hello,

I am trying to take multiple measurements using a PXI4070 DMM. The goal is to take a user selectable number of samples every 1 mllisecond and average the samples. The code works and takes the appriate number of samples. The issue is the lenth of time of the samples are taking too long.

For example, I have been using 10,000 samples(Number to Read) which I would expect the take 10 seconds at 1ms per sample. This setup is taking about 16 seconds to complete. I found a NI example "Acq Multiple Sample - Interval Dample Trig", it is taking the same amount of time to complete the 10,000 samples.

I've tried using the wait ms timer in the and out of the event structure, this was no help. Am I not understanding the operation of the interval VI?

 

Thank you,

Dave

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Disclaimer: I am not familiar with DMM.

I tried to read about the example: from Source : http://zone.ni.com/reference/en-XX/help/370384N-01/dmm/examples/

Acq Multiple Samples-Interval Sample Trig

This example acquires multiple measurements continuously. The first measurement is acquired without a trigger. Each measurement thereafter is acquired when Send software trigger function is called. Select the measurement function, range, absolute resolution and power line frequency.

-So i believe after the first measurement for every next measurement it is waiting for a trigger which comes after 1ms interval.

-Instead set the sample trigger to Immediate and then it should work correct because it doesn't wait for triggers and no delays in between taking measurements.

Thanks
uday
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uday,

Thanks for your reply.

Setting the sample trigger to immediate caused the 10,000 samples to be taken in about 6 seconds.

 

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Dave,

 

A couple of things here:

 

First, it may be worth posting to the DMM Board as the users there will be much more familiar with the Hardware and Software you're using.

 

Second, What is the end goal of taking several measurements and averaging them? If you are looking to get a more accurate but slower reading setting the resolution up to 7 Digits is a better way to do that.

 

In the help for the niDMM Configure Multi Point VI it states that Sample Interval "sets the amount of time between measurement cycles." Each cycle takes time to complete and then the interval timer is started again. The DMM takes a significant amount of time because it is sampling multiple times and averaging internally, see point 2 of the linked KnowledgeBase article for more info.

Reducing Noise with DMM Measurements

Alex W.
Applications Engineering
National Instruments
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Alex,

Thank for your guidance about the forum, I am newbie to the forums.

The goal is to allow a user to input the number of samples to be taken, then the number of samples is taken at 1ms intervals.

I will review the KnowledgeBase article, if I continue to have issues I will re-post in the proper forum.

Thanks,

Dave

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