How to set sampling rate for CRIO 9074 to get better measurements

[meharda_92]

I have CRIO9074 and NI modules NI9227 (current) and NI 9225 (voltage) for measurements.

I am measuring the current for load emulator and voltage for grid simulator, but I am unable to set up the sample size/ sample rate for accurate measurement, the sine wave is not accurate. 

How to get RMS values and power values with accurate sine wave.

I applied 230V 50Hz and load about 1-2kW range.

Thanks

[GerdW]

Hi meharda,

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@meharda_92 wrote:

I have CRIO9074 and NI modules NI9227 (current) and NI 9225 (voltage) for measurements.

I am measuring the current for load emulator and voltage for grid simulator, but I am unable to set up the sample size/ sample rate for accurate measurement,

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You are using the ScanEngine interface with your cRIO: this is quite limited to low samplerates! That old 907x device is limited even more to about <=200Hz… You may try to lower the ScanEngine update rate, but less than 10ms might be hard to reach.

When it comes to high samplerates (with low jitter) you should use the FPGA in your cRIO. Do you have access to the FPGA module with your LabVIEW installation/license?

(If possible you should upgrade the cRIO chassis to something more recent, like the 905x line, to get much more processing power. The 907x line isn't supported very well nowadays, it's "end of life"…)

On your VI:

• Why do you use a DBL control to set the iteration time with Wait(ms)? Did you notice that coercion dot?
• Why do you use ever-growing arrays in feedback nodes? Did you do the basic Realtime programming trainings to learn the pitfalls of Realtime programming?
• Why do you use graphs in a headless Realtime device?

[meharda_92]

I can access the FPGA module with LABVIEW and I am using DBL control to change the sampling time and see the impact on graphs (if they are accurate or not), after getting final sample rate/time then I will fix it

I used the graphs to see the current and voltages waveforms.

[GerdW]

Hi Meharda,

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@meharda_92 wrote:

I can access the FPGA module with LABVIEW

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Then you should get rid of the ScanEngine and implement DAQ within the FPGA…

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@meharda_92 wrote:

I am using DBL control to change the sampling time

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That doesn't make sense when the Wait function only accepts integers…

(It also doesn't make a lot of sense in the ScanEngine context.)

[rolfk]

Also note that with the cRIO-904x and 905x series you may be able to use DAQmx on the controller to achieve significant higher sampling rates than with the Scan Engine, without having to create a dedicated FPGA personality yourself.