floating voltage DAQ card

[AMRC]

I use a DAQCard - 6062E to take measurements from an accelerometer in a vibration software package. We have problems with floating voltage just with the system setup, not even taking measurements. There is an option in the software package to switch off analogue ground reference. Would this solve our problem? If so will it effect the accuracy of measurements? Also is there a method of grounding the laptops we use to measure with? I have read about resistors, grounding cables etc..

Any help really appreciated.

Thanks

[MarkLe]

Hi AMRC,

Generally you would want to turn off the analogue ground referencing only if your transducer is also referenced to an Earth, to avoid the possibility of ground loops. These occur when there is a potential difference between the ground at your transducer, and the ground at your measurement end (the DAQ card), which then gets added onto your signal if the measurement is made with refernce to ground.

As your DAQ card is on a laptop, it probably isn't grounded to mains Earth, so shouldn't be affected by the state of the analogue ground. I don't think there is a way to ground the chassis of the laptop to Earth.

For some more details of how to make signal connections to the 6062, please have a look at the manual for the card, which you can find here:

http://digital.ni.com/manuals.nsf/websearch/8C2127721F4272D6862568C400525BA6

There are some details of the best ways of making analogue input connections in Chapter 4, specifically from page 37 onwards.

If you have our DAQmx drivers installed, you should also have an icon to use Measurement and Automation Explorer (MAX), a test utility which you can use to check the board is installed correctly, and run some simple tests on the channels. This may help identify where your problem lies. If not, you're reliant totally on the 3rd party software to setup the analogue input lines correctly.

Good Luck!

Best wishes,

Mark

Applications Engineer

National Instruments