Data acquisiton using NI-USB Daq 6210

[Pollux]

Hello,

Background:

I am trying to build an application to monitor the power line of a factory because it is very noisy and we get quite often line stops that affect production.

I designed a data acquisition program in Labview using a NI-USB DAQ 6008. It works but the results are not satisfactory since I only have 3kHz per channel (I use 3 channels) so I don't get to see higher frquencies that probably are the reason of our problems.

So I switched to NI-USB DAQ 6210. This way I have a 13kHz acquisition rate so I get acces to the 13th harmonic (b.f. 50Hz) and do some oversampling to avoid aliasing.

To acquire the signals I use a separation transformer 400V/4V.

Problem:

I have tested my application in lab, trying to measure a DC voltage of 5.5 Volts and this is what I get:

I would have expected to have a continous line since it is a DC voltage that I put on the channels. Repeating the test for other voltages gave similar results. It's like loosing the signal for some fractions of a second.

You can see here the configuration of the acquisition task in MAX:

I have done the physical connections on the board acording to the indications that MAX gives for Differential measurement.

I have also tried to do a calibration. It seems to saturate above 4V as you can see below:

It is true that this calibration is done with a standard DC power source that probably has a deviation of tenths of milivolts. I have also tryed with a precision source from Fluke that the Metrology department has but I don't get better results.

You can also find a calibration report attached.

Supposing that the board is deffective I exchanged it for another of the same type (6210) but I have the same problem. It is also possible that both boards are deffective since I don't know their history before my arrival in the company.

What do you think is the problem?

Thank you.

calib.html

[Tim_S]

Just as a note, if you're out of range with a power supply is 5.5 V and DAQ channel setup of +/- 5 V. I would expect the value to be at the rail rather than the plot you have.

Edit: The use of the transformer may very well remove the transient you're looking for.

Edited April 26, 2012 by Tim_S

[Pollux]

Could it be that the information quantity is more than the USB can acquire? I'm not sure if on that computer I have USB 2.0. It's an old laptop from 2004 so it could be that it has only USB 1.1.

edit: on second thought it can't be. I also tried a 3 kHz acquisition and it didn't work...

I suppose the boards are broken.

Edited April 27, 2012 by Pollux

[JamesMc86]

Simplest thing is to try it on another PC to rule this out (tech support will probably ask this anyway if you get it fixed).

I would confirm it with another source. Also what if you jut ddo one channel? But sounds like it could be a fault. Especially if you've had to recalibrate the volts

(null)

[ShaunR]

Your signal is 20ms (50Hz). That's mains leakage (either in your source or in the USB supply). Change the source to a battery and see if it goes away. If it doesn't, send back the unit and get a replacement.