Measure current and voltage with daq

[053647967]

Hello!

My name is Alan and I'm student of electrical engineering. I'd like to measure current on primary winding and voltage od secondary winding. For current measuring I use Current clamp wich converts current into voltage. I put current and voltage firstly on oscilloscope and then on daq that I acquire them using labVIEW.

I get voltage the same as on oscilloscope, but problem is with current. I get it sinusoidal on oscilloscope, but on labVIEW I get some strange shape. values looks proper, but the shape doesn't. I tried with different grounds, but didn't work. 

I hope it makes sense what I wrote. I'm sorry about my English. Your advises would be much appreciated. 

PS: I'm actually measuring BH loop of some material.

Regards Alan

[Stefo]

Hi Alan,

Try to check if input configuration is the same on both devices - in your case I believe would be the best to use differential. If the shape is different between devices, you could verify that the sampling rate of scope is proper - your scope might be using equivalent time sampling which you distort shape in some cases. Verify that you use real time sampling. DAQ board will have it by default, it is more challange to use ETS with it.

regards,

stefo

[JÞB]

Hi Alan-

My first guess is that you are using a USB-6008 or some other student device to measure the output of your current clamp.  The input impedance of a 6008 is 140K ohms this will load down the signal from the clamp and give you inaccurate data.

Most of these clamps have a very limited ability to drive a load (a 10 Mohm DMM or O'scope input impedance is what they are designed for.)  You need either an AI device with similar input impedance or some sort of isolation driver.