setting sampling rate of strain data on"stran - continuous input.vi" from example source of labview

[Daniel_Kil]

I want to log strain data as 20 samples/sec.

but when I use tran - continuous input.vi" from example source of labview, can not find that how to set this.

I can not understand clearly about meaning of  'samples per loop', 'sample clock source', 'sample rate' in this VI

actural sample rate is fixing to 793.65 even I changed value of 'samples per loop', 'sample rate'

Please help me about this issue.

[GerdW]

Hi Daniel,

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@Daniel_Kil wrote:

actural sample rate is fixing to 793.65 even I changed value of 'samples per loop', 'sample rate'

Please help me about this issue.

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Please tell us which DAQ hardware you use.

Did you read the manual/specs for your DAQ device? It surely mentions the supported range of samplerates…

(Educated guess: you use one of those NI modules where the samplerate usually ranges from ~1.6kS/s to 50kS/s.)

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@Daniel_Kil wrote:

I can not understand clearly about meaning of  'samples per loop', 'sample clock source', 'sample rate' in this VI

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There's a simple relation:

iteration_time [s] = samples_per_loop [S] / sample_rate [S/s]

The sampleclock source provides the trigger signal for the ADC (to read the next sample) and most often you will use the "onboard clock". You might use external clocks or other clocks provided by your DAQ device when there are reasons to do so…

[Daniel_Kil]

I am using NI-9234 module with NI cDAQ-9178 chasis

Data rate range (f_s) is Min. 794S/s, Max. 10kS/s

However, I want to save data only 20S/s for synchronizing with load(voltage) data.

How can set this?

[GerdW]

Hi Daniel,

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@Daniel_Kil wrote:

I am using NI-9234 module with NI cDAQ-9178 chasis

Data rate range (f_s) is Min. 794S/s, Max. 10kS/s

However, I want to save data only 20S/s for synchronizing with load(voltage) data.

How can set this?

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You cannot set a samplerate of 20S/s as the module doesn't support it.

But you can set 10 (or 5 or 2.5) kS/s and decimate down to 20S/s! When sampling at 10kS/s you read 500 samples and average them to yield just 20 samples from 10kS per second…

Btw. according to the specs the NI9234 only supports:

Data rate range (fs)
Using internal master timebase Minimum 1.652 kS/s Maximum 51.2 kS/s

So you may set a samplerate of 2.56kS/s and decimate by a factor of 128…

[Daniel_Kil]

Thanks for your kind support.

Can you help me know how to set sample rate to save data?

I can under stand about reading sample rate. so can read strain data in multiples of the voltage data.

so. hope to saving data after synchronize with other source after reducing sample rate.

Best regard.