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USB-6259 to capture the current waveforms

Hi all,

        I am pretty new to LabView and data aquisition. Sorry to bother you all. I have a question:

 

"Can I use the USB-6259 DAQ device to capture the current waveform of electrical appliances e.g. electric kettle using current probes????? If yes, could you be very kind to guide me in this regard???"

 

         Thanking in anticipation.

 

Best regards,

Haroon

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Message 1 of 10
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Yes, you can do that.  You need to do the following:

 

1. Put a shunt resistor (1ohm, high precision, high wattage) in series with your application.

2. Use one of the Analog input from your DAQ to measure the voltage drop across the shunt, and this will be your current waveform, since the resistor has 1 ohm.

 

Things to watch out for:

1. Power rating on shunt: make sure your shunt can handle the power.

2. Noise: you may need some filtering circuitry to get rid of the signal noise.  If you are comforable with digital filtering, you can use some of the filtering function in LabVIEW.

3. Level at AI: maybe very low, since there are little drop across the shunt.  If you don't mind a larger voltage drop, you can increase the value of the shunt to increase the level; if you just want to look at the pulse shape.  Or, you can put an amplifying circuit for a little boost before you feel the signal to AI.

 

Yik

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Message 2 of 10
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Are the appliance powered by AC mains (ie 120VAC, etc?). If so I would use some method of isolated measurement.

 

-AK2DM

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"It’s the questions that drive us.”
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Message 3 of 10
(1,798 Views)

I agree.  You probably need isolation as well.  It seems like you have to do some signal conditioning.  You can try opto20.  However, I would recommand that you just go get a SCXI or CompactDAQ for your purpose.

 

Yik

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Kudos and Accepted as Solution are welcome!
Message 4 of 10
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Thanks for the replies. Yes I'll use it with the AC main supplies (230 Volts). I am thinking of using 0.5 ohm resistor which means voltage will be in the maximum allowable limit for the interface.

I want to take the FFT transform of the the waveform.

I am just a beginner in the field of research. Why would I need isolation???? Because I think 0.5 ohm resistor will make sure that voltage applied is safe.

 

your guidance will be highly appreciated.

 

Best regards,

Haroon

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Message 5 of 10
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Haroon:

 

I would suggest a current transformer or Hall-Effect based current clamp or transducer. These will provide full electrical isolation between the mains and the DAQ card.

 

You may need to pay attention to what your highest frequency component is to determine the bandwidth needs of the sensor and the sampling rate you need to use for your DAQ card.

 

The use of a cuurent sense resistor is a BAD IDEA in this application. What happens if your device under test has a short circuit- then it will apply the full 230VAC across your sense resistor and the DAQ card leading to destruction of equipment and a potentially hazardous situation to personnell.

 

Be aware that many types of equipment- specifically pumps, compressors, motors, motor drives and inverters can easily draw currents over a magnitude larger than their steady state current draw.

 

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
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Message 6 of 10
(1,749 Views)

I guess if a shunt is dangerous, you can use a contactless sensing component for current.

 

Yik

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Kudos and Accepted as Solution are welcome!
Message 7 of 10
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Thanks for the reply. I have got a current probe now to use. But, there is a lot of noise in the signal. How can I filter it out???

 

 

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Message 8 of 10
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What is the make and model of the probe?

 

What is the load that you are measuring current on?

 

Can you attach some screen shots of the waveform?

 

What sampling rate, input range and mode are you using for the DAQ?

 

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~
Message 9 of 10
(1,635 Views)

The highest freqeuncy would be 3 kHz. now you suggest me what should be the sampling ferquency and number of samples.???? Another thing is that, should I use floating signal or ground referenced signal type on the DAQ????

Anxiously waiting for reply.

 

best regards,

Haroon

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Message 10 of 10
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