Successive identical values from DAQmx temperature recording

[etiennedm]

Hi, 

I have made a simple VI following tutorials from DAQmx to record two PT100 sensors. I have attached the VI and the PT100 datasheet here.

When plotting the output of a recording at 10Hz, I am suprised to have successive identical values by groups of 4 (see the attached plot I've made). It does'nt make any physical sense to me, so I guess I am missing something in the LabView implementation but I can't see what.

Note that if I run the VI at 5Hz, I got successive values by groups of 2, 20Hz, groups of 8, etc...

Any help would be very much appreciated !

[etiennedm]

The attachements were not uploaded correctly, sorry... Here they are

[Tom_Powers]

Can you save your program in to LV2018 or better yet LV2012 so that everyone can see it.

Are you configuring the devices in MAX or reading the signals and converting them to temperature in software?  If you are doing it in MAX I would bet that this is where it is getting slowed down.

[RavensFan]

Which DAQmx module are you using?

[GerdW · Accepted solution]

Hi,

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@RavensFan wrote:

Which DAQmx module are you using?

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To explain this with some more details:

Typical Pt100 measurement modules are rather slow, as the NI9217! In "slow mode" it needs 200ms to measure one (1) channel! Only when you switch to "highspeed mode" you can expect 400S/s (aggregate) from that module!

So please read the datasheets of the (DAQmx) devices you use to measure your Pt100 sensors…

[etiennedm]

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Can you save your program in to LV2018 or better yet LV2012 so that everyone can see it.

Sorry I didn't know one can not see a vi of a later version, I'll upload a LV2012 vi for my next posts.

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Typical Pt100 measurement modules are rather slow, as the NI9217! In "slow mode" it needs 200ms to measure one (1) channel! Only when you switch to "highspeed mode" you can expect 400S/s (aggregate) from that module!

Thank you for pointing that out @GerdW, that was my issue. I am working with the NI9217... I only looked at the software documentation so I didn't find this info...Next time I'll read both hardware and software doc. I have attached the updated vi in case anyone need it.

Thank you very much guys