Instrument or DCS signal filter 2

[controlnovice]

Should an analog signal be filtered in the instrument itself, if available, or shoud we have the DCS/PLC filter the incoming signal.

For example, many instruments will allow a first order filter on the output of the 4-20mA signal.

Our DCS will allow us to do the same thing with the incoming signal. I don't want both doing the same thing, so which one is the better location?

It makes sense to have it all in the same location: either all in the various instruments or all in the DCS, but I'm sure not all instruments will offer this option.

Which is better?

Any suggestions?

 

[buzzp]

I would say the best location is the device that is USING the signal and not the one that is GENERATING the signal. The wires running through an industrial or otherwise noisy environment will pick-up some trash (although common mode noise is all but eliminated by the twisting of the wire) on its way to the equipment that is going to use it. To me, the best location is where it will be used.

 

[khan101]

Best Location? in DCS itself. If you start doing things like that in field, then it will be hard to track them and document them all. Usually more than one technician is responsible for field instruments but DCS is under one or two engineers and they can keep track of changes more easily. That's my opinion and that's how we do it here on our site.

 

[hacksaw]

some times you have to condition the signal at both ends. agreed that signal conditioning in the field is not desireable, but you will occasionally find it necessary. It must be coordinated not only with you dcs filtering but also with the controller tuning.

 

[buzzp]

The cases of filtering in the field (output of device providing the signal) and then filtering the same signal in the DCS makes no sense. Why not just use the filter at the DCS (assuming both filters have the same attentuation at the respective frequencies)? I say your wasting your time and effort to filter at both locations.