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[Need Help] DC Measurement: Need more than 1 value/sec.

Hi,

 

I am measuring a dc voltage signal from a sensor using NI 6251. My goal is to acquire a DC measurement of the signal and save it in a spreadsheet file.

 

In LabVIEW, i used the Express DAQ Assistant with Samples to Read at 1k and Sampling Rate at 1kHz. I then connected it to a low pass filter, then to the Express Amplitude and Level Measurements for a DC Measurement. Finally, I connected it to Save Measurement File.

 

My problem is this: I only get one (1) dc value per second in my spreadsheet file. I wish to have at least 100 dc values per second but I do not know how to do this. I am aware that the DC value is somewhat an average of a set of samples. Maybe I could try to increase the sampling rate to 10kHz and probably get the DC Value for every 100 samples but I have no idea how to implement this.

 

Could anyone help me?

 

With best regards,

Jason

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Hello Jason,

 

I would really like to help you with this problem you are having because it should seem with your configuration you should be receiving at least 1000 samples per second. Would you be able to post your VI so that I may have a look at it?

It may also help to tell me whether you are using the PCI-6251 or USB-6251.


Alex Thomas, University of Manchester School of EEE LabVIEW Ambassador (CLAD)

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@Crispo wrote:

Hi,

 

I am measuring a dc voltage signal from a sensor using NI 6251. My goal is to acquire a DC measurement of the signal and save it in a spreadsheet file.

 

In LabVIEW, i used the Express DAQ Assistant with Samples to Read at 1k and Sampling Rate at 1kHz. I then connected it to a low pass filter, then to the Express Amplitude and Level Measurements for a DC Measurement. Finally, I connected it to Save Measurement File.

 

My problem is this: I only get one (1) dc value per second in my spreadsheet file. I wish to have at least 100 dc values per second but I do not know how to do this. I am aware that the DC value is somewhat an average of a set of samples. Maybe I could try to increase the sampling rate to 10kHz and probably get the DC Value for every 100 samples but I have no idea how to implement this.

 

Could anyone help me?

 

With best regards,

Jason


You need to understand some basic arithmetic. With a sample rate of 1000S/sec and 1000 samples, that will take 1 second to acquire and then the express VI will reduce that to a single sample. You are getting exactly what you have programmed. Basic arithmetic would tell you that if you requested 100 samples, that would take .1 second and you would have 10 readings in your file. Request 10 samples which would take .01 second and voila, 100 readings.

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