How do I filter out AC noise on a load cell?

[otte]

I am attempting to get an accurate DC voltage reading from a load cell. In my application, the load cell is near a motor and motor controller and is picking up a considerable amount of electrical noise. I attempted to use a Butterworth filter but had no luck. What is the best solution to this problem?

[rpursley8]

A sharp Butterworth filter will work (let's say 12th order with a cutoff freq of 1-2 Hz). the easiest way might be to average over a larger number of points to average out the 60 Hz (or 50 Hz) signal.

[trussell]

Are your wires going to the sensor a twisted pair? If they are not, then try it. In a true differential measurement, the AC noise will effect both wires in the same way if they are twisted. Then the differential measurement will minimize it's impact.

[Conseils]

Noise is always best removed at source.

Ensure there is:-
An EMC filter fitted to the motor controller.
Correctly screened motor cables.
A shielded and correclty grounded shield on the cable between the measurement system and the sensor.
An anti-alias filter to the channel input.
Terminate unused input channels correctly.
An EMC filter on the computer.

For some of this work a COMPETENT PERSON is required as defined in your local electrical systems regulations if the supply voltages exceed 50v.

Let us know if any of these were in place?

Message Edited by Conseils on 04-18-2005 08:08 AM