sample rate

[Nathan_Blanc]

i am now doing the first labview tutorials, using a simulated hardware

my simulated hardware is the NI 9201 voltage meter. i am trying to reduce the sampling rate below the frequency of the phenomenon (1 hz) but it won't go bellow 1.6516 Khz. i read somewhere that there could be a minimal sampling rate for the device but couldn't find any thing in the manual about it. would be thankful for any help

nathan

[GerdW]

Hi Nathan,

the datasheet only mentions the upper limit of 800kS/s…

Then there will be other problems: do you mind to attach your VI? How did you define the samplerate?

(For such small frequencies (below 1Hz) you might even read single samples in a simple while loop with a wait function…)

[Nathan_Blanc]

attached is my VI. many thanks

nathan

[GerdW]

Hi Nathan,

this is not a VI, it's just an image.

It doesn't look like LabVIEW ("classic" version) or MAX, and it doesn't show any interesting details. How did you simulate the device?

[Bob_Schor]

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@Nathan_Blanc wrote:

i am trying to reduce the sampling rate below the frequency of the phenomenon (1 hz) but it won't go bellow 1.6516 Khz.

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I am trying to imagine why you would want to sample below the frequency of the phenomenon.  Suppose something happens once a second and you took a sample once an hour -- what is the probability that you would "record" the event?

One generally tries to sample several times faster than the highest frequency of the event.  If an event is happening once a second, sampling at 10 Hz might be reasonable.  If you are worried about accumulating too much data, you could save (with a timestamp) only those samples that "showed something", I suppose ...

Bob Schor

[Nathan_Blanc]

i wanted to test what you said exactly. to see that when i sample below the phenomenon frequency aliasing can occur. this is also the point the tutorial is trying to teach me.

like you said, for actual purposes 10 hz sounds reasonable, but 1600 hz sounds a bit of an overkill. as i said, for some reason the program does not allow me to change the sampling frequency to 10 hz. 

in any case, "time stamps" sound like a plausable workaround. how do I save with a time stamp?

nathan

[Nathan_Blanc]

this is labview NXG, am i in the wrong forum? regarding the attchment, should i attach the project? the task?

[Bob_Schor]

The more you attach, the easier it is for us to understand what you are trying to do and can see the details of how you tried to do it.  Most Projects reside in a single folder -- if you right-click the Folder, you can "Send to" a Compressed (.zip) file, and thereby including (almost) everything.  

Bob Schor

P.S. -- LabVIEW and LabVIEW NXG share a Forum.  I don't remember where, but you can put an NXG "Flag" on your Post that, I think, shows up on the upper left corner when you view the Post.

[GerdW]

Hi Nathan,

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@Nathan_Blanc wrote:

like you said, for actual purposes 10 hz sounds reasonable, but 1600 hz sounds a bit of an overkill. as i said, for some reason the program does not allow me to change the sampling frequency to 10 hz. 

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Are you sure about simulating a NI9201 module?

Maybe you selected a different module, as there are several of them allowing minimum sample rates of ~1.6kS/s…

[GerdW]

Hi Nathan,

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@Nathan_Blanc wrote:

this is labview NXG, am i in the wrong forum? regarding the attchment, should i attach the project? the task?

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You should see this when you start a new topic:

This also is mentioned right at the top of the LabVIEW board…