Hi all

I want to avoid noise from my sensor output signal..previously sensor output wires were tied with power cables and I removed it and separated but still I am getting the noise and my system becoming unstable.

If I put my sensor cables in a iron pipe and ground it, will solve my problem?? Pls advice..

 

Are you using a twisted, shielded pair for your sensor signal wiring (presuming it's a two-wire circuit)? If so, is the shield drain wire grounded at <b>ONE</b> end <b>only</b>?

It doesn't make any difference which end it's grounded at, but "convention" is that it be grounded at the power source for the circuit, which is usually, but not always, the control system. So, they are usually grounded in the control system panel, near the termination of the circuit wires.

The drain wire should NOT be grounded at both ends. It sets up a loop which is very bad for noise.

Properly grounded shielded wiring, properly separated from power (high-level) wiring, is usually more than sufficient. It shouldn't be necessary to use metal pipe and try to ground it at one place.

 

You probably need to make a concerted effort to find out where the noise is coming from. If it is noise induced in the cabling, the pipe may help. If you have ground loops and inadequate bonding, it may not. In a few circumstances, it can make things worse. With the cheap to rent or own DSOs available now, one can find out a lot with spectrum analysis. You get clear signatures from power harmonics, VFD switching, etc. and this can save a lot of effort if paying attention to the grounding doesn't work. Most of the noise problems I've seen are because automation folks aren't very careful with power distribution and grounding. And they don't think at all about noise unless the thing doesn't work :^).

Regards
cww

 

Probably, you are using an analog (voltage or current) sensor output. Why not to use a sensor with frequency output? Frequency as an informative parameter at sensor's output is most noise immunity signal. You can select frequency output sensors form www.sensorsportal.com/HTML/Sensor.htm

Good luck.

 

Are you sure its noise being induced in the cable? Have you verified that this is not noise coming from the sensor itself, installation problems, process problems, incorrect filtering, variable process, air in your fluid flow etc?

Rob
www[.]lymac.co.nz

 

Hi all

This link is an article directly related to your noise problem. It should provide a solution.

http://www.wici.com/technical/manuals/wiring.pdf

Emmett