# The Daily CLAD

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## CLAD2017 - Hardware - DAQmx - Find those values

Active Participant

Consider the VI, which of the following values for Sample Rate and Samples/Channel resulted in the data shown in Waveform Graph?

Member

i think its a) because of the x-axis scale: (5/2000) = 0.0025

Knight of NI

If this was a waveform chart, I would go with A.  Otherwise, none of these answers make sense to me.  The waveforms go for 5.5ms.  So a sample rate of 2000 makes sense.  But the number of samples would be 12.

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Member

answer should be A, except A all the above will take more than 0.0025 seconds......

Member

I agree with the others, none of the given options is fitting the graph.

The Sample Rate seems to be 2000samples/second but the samples/channel is neither 5 nor 20 but probably 12.

Member

a) SR 2000 (0,5ms) multiplied with 5 samp => 2,5 ms time span => no valid answer
b) SR 1000 (1,0ms) multiplied with 10 samp=> 10ms time span => no valid answer
c) SR 1000 (1,0ms) multiplied with 15 samp=> 15ms time span => no valid answer
c) SR 2000 (0,5ms) multiplied with 20 sampl=> 10ms time span => no valid answer

Reverse test: I am only able to count 10 samples instead of 12
For 10 samples we need 0,006 sec
For 1 Sample we need 0,0006sec
=> Rate could be approx. 1666
So Sample rate of 1666 and Samples/channel of 10 could be close to the answer.

Member

Looks to me that the elapsed time is somewhere near to 0.0055 seconds.

& I think I can count 10 samples across the traces.

So the period of the sampling is somewhere near 0.00055 seconds

which is the same as 1.82 kS/s (1,820 samples per second)

Available sampling rates for NI-9234 & NI-9237

If the device was NI-9234, out of the box it will do 51.2 kS/s divided by "N" where "N" is an integer 1 to 31.

When a sampling rate is called for, the nearest possible sampling rate is set.

If "N" is 28, then the valid sampling rate is 1.828 kS/s (which 1828Hz  and this will be set for a 'requested' sampling between about 1795 to 1861Hz)

So if NI-9234 was the hardware, a sampling rate of 1800 Hz and 10 samples/channel would give the waveform graph shown.  (I thought this might be near one of the possible answers, but it isn't.)

Good practice: Ask the hardware what rate it actually set.

Displaying this value can help to explain what has happened!

Member

In Graph shown by white line, i can see two clear peaks which are 0.6 milisecond apart so rate is (1÷0.6ms) = 1666.66 and as crossrulz said waveform goes for 5.5ms so number sampels per channel equals to (5.5ms÷.6ms) = 9.16 or we can say 10. but none of the option fill this requirement.

Still i guess answer is  A.

Trusted Enthusiast

b)

Regards
Ray Farmer
Member

A...

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