Variations in reading of real time data

[tronoh]

Dear Sir

Good Day

I am using LabVIEW 2012, NI DAQ 6281 to measure analog data from current sensor. The plot of that data showing different values at each loop count. I have attached the file to show the results for three loop counts. Can any one explain me why this variation is coming. (Ideally it should be same value at each loop count). The connection scheme which is in differential mode is also shown in attached file.

Waiting for your reply

Kind Regards

Urfee

[srikrishnaNF]

Hi tronoh,

 I had one question to ask..

 Q1)As NI DAQ-6281  is M-series data acquisition card as per http://sine.ni.com/nips/cds/view/p/lang/en/nid/209153..

       And you are telling that you acquired data from a current sensor.How you are acquiring data from a current sensor?and which type of current sensor are you using?

Coming to your question,there will be many factors which governs the acquisition like external noise and also on the connections as well.

Regards,

SrikrishnaNF

[tronoh]

Dear Sir

The connection scheme I have already attached in word file. The connections are in differential mode. The current transformer that I used is used to measure the induction motor line current. Its hall effect type sensor. The model of the sensor is SCT013 5A/1V (WWW.YHDC.COM). Attached is the picture of Current transformer that I used.

Do you think that environmental noise could be the reason? If yes then how we can eleminate it.

Kind Regards

Urfee

[crossrulz]

For future reference, just post the pictures instead of putting them into a Word document.  If you have more than 3, then zip up your files.  Many people will avoid MS Office files since they can contain viruses.

This doesn't look like a noise issue.  It is a phase issue.  Meaning, when you start acquiring data.  If you told the DAQ to acquire the right number of samples to get EXACTLY one period, then you shouldn't see this.  But that is really impossible to do.

What you might want to do is change your graph into a chart.  The chart keeps a history of the signals it was given.  That will give you a better idea of what is happening.  I would also recommend performing a Mean and RMS measurement on your waveform to prove that it isn't changing.

[tronoh]

Dear Sir

I will use pictures instead of using Word file in future.

I have replaced the graph with chart but still that variation is coming. Actually I want to measure the phase angle of fundamental component. Ideally phase angle and frequency of fundamental component i.e 50 Hz should remain constant. But here in results, its varying. So I could not understand why this happening.

[shjeong]

As you know most current sensor(SCT013) output are floating grounded signal.

It means reference was not fixed and signal is easily affected by power line(like 50Hz or 60Hz).

I think you need to connect AI-(34) to AI-GND(67) or  AI- to AI GND with resistor( 10K Ohm )

refer to the manual http://www.ni.com/pdf/manuals/371022k.pdf  ( page 4-15 to 4-24 )

Regards.

SungHoon,Jeong