Variable Rate DAQ Assistant

[T1p1ca1]

How would you alter the rate of the DAQ assistant on the fly at certain time intervals then write them. I currently can get the rate to change going into the DAQ Assistant however when I pull the data it pulls over a 1000 points during the testing interval of 1 sec no matter what I do even if the rate input is between 1 and 5 Hz. Would this be a case where my hardware can only sample so slow and I need to manually in the code parse it down with something like average blocks of data in an inline statistics module?

PS: I started using Labview about 12 hours ago so if there are glaringly obvious fixes I would appreciate those as well.

Running on a cDAQ 9178 Chassis with a NI 9237 to bring in data from a load cell into Labview 2020 64-bit.

[GerdW]

Hi T1,

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@T1p1ca1 wrote:

when I pull the data it pulls over a 1000 points during the testing interval of 1 sec no matter what I do even if the rate input is between 1 and 5 Hz.

Running on a cDAQ 9178 Chassis with a NI 9237 to bring in data from a load cell into Labview 2020 64-bit.

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Please read the datasheet of your hardware first!

The NI9237 is somewhat special and limited in the supported samplerates! Samplerates of 1…5Hz aren't supported, that module will start at ~1600S/s…

On your VI:

Using DAQmx functions is rather easy after reading this (and learning from all those example VIs in the example finder). You really don't need the DAQAssistent…

[T1p1ca1]

Even if I ultimately need to pull from 16 load cells for a month straight? The reason I went with the DAQ Assistant is that it can manage all those channels rather easily with different scales for each load cell. I may not have explained this correctly the first time I apologize

[GerdW · Accepted solution]

Hi T1,

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@T1p1ca1 wrote:

Even if I ultimately need to pull from 16 load cells for a month straight?

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Especially in this case!

The DAQAssistent is fine for a short and quick test. For "professional" usage you should get rid of that ExpressVI very fast!

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@T1p1ca1 wrote:

The reason I went with the DAQ Assistant is that it can manage all those channels rather easily with different scales for each load cell.

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You can do so also very easily using plain DAQmx functions…

[johntrich1971]

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@T1p1ca1 wrote:

Even if I ultimately need to pull from 16 load cells for a month straight? The reason I went with the DAQ Assistant is that it can manage all those channels rather easily with different scales for each load cell. I may not have explained this correctly the first time I apologize

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Especially if you need to pull from 16 load cells for a month straight. All of this is much more straight forward with DAQmx functions.

Edited to add: Looks like GerdW beat me to it.

[T1p1ca1]

I am stuck using a NI 9237 to retrieve data from 16 load cells for a month. I need to lower the data acquisition rate to a more manageable level and change it on the fly from 50 to 1 to 0.000278. I was looking into changing the master time base to something slower since the spec sheet says that it's possible. Has anyone had luck doing this.

NI9237 - cDAQ9178 - Labview 2020 64-bit

[GerdW]

Hi T1,

I merged your threads because it's basically still the same problem…

Why don't you live with the supported sample rates of the NI9237 module?

I would:

1. set a sample rate of 2500S/s
2. read blocks of 500/625/833/1250/2500 samples and average them
3. now you get values at 5/4/3/2/1 Hz, respectively!

Bonus: changing the number of samples to read "on the fly" is very easy, much easier than to change the samplerate of a DAQmx task…

[T1p1ca1]

The problem is that I don't know how to setup those blocks of data I would know how to set that up in DASYlab but not in Labview. Like I literally don't know where those modules or functions would be. That is actually what I was planning to do from the beginning but I didn't see a way to do it.

Edited: This file is where I'm at now after you telling me to use the DAQmx modules.

[GerdW]

Hi T1,

why don't you start with a simple VI? Learn step-by-step!

Set the "number of samples" as suggested before…