Signal to Noise Ratio

[jlahir@modwind]

We are using the following hardware with Labview to measure load:

CDAQ mX 9172

NI 9219, 9205,9264, 9485.

The signal form the load cell is amplified before it is read by LABView

All Cables are shielded.  The cable lengths between the load cell and DAQ is 150 ft.

We are experiancing noise in the signal being read by the DAQ. This nose occurs only when the winch that is exerting the load on the load cell is operating. 

We have checked the grounding for the entire circiut and rectified a few faulty connections.  This had brought down the noise a little bit.

We would like to get some inputs as to the possibilites that we may have overlooked that are causing this noise.

Also, is there a SNR specified for any of the above mentioned hardware.

Thank You

[AnalogKid2DigitalMan]

What type of motor does the winch have?

Is the motor case grounded?

Cabling- shield grounded at one end only? Twisted pairs used?

150' is a bit of a haul for low level signals.

Location of amplifier- if near PC, it will amplify all the noise too. If near winch, it may still pick up noise. Amplifier is a metal enclosure and grounded?

-AK2DM

[Enrique Jimenez]

Are you using the 9205 or the 9219 to take the measurements? Take into account that the 9219 is channel to channel isolated while the 9205 is only isolated from the chassis.

Is there a way you can test the quality of the signal coming into your amplifier? Is there a risk you may have a noisy amplifier? The noise you are seeing has a pattern? (i.e. 60Hz noise or whatever frequency the winch runs to?) If you can provide a diagram of your setup and a capture of the noise it would be great.

Enrique