Noise supression

[jrb5879]

Does anyone have any ideas on getting rid of unwanted 60 cycle noise on a 4-20ma 2 wire circuit? thanks

 

[IRstuff]

There isn't supposed to be any noise, which means that either it's not wired up correctly or it's not twisted-shielded like it's supposed to be.

Obviously, if the noise is too large, there may not be anything you can do about it short of shielding everything.


TTFN

 

[jrb5879]

The wire is shielded and grounded on one end. The problem is intermittent, it will go for months and then start driving the plc crazy.

 

[busbar]

If the 'loop' pair is carried in metal raceway, there may be intermittent leakage from ground to the shield part way through the run. Isolating the cable and megging at 100 {not 1,000} volts might flush out the problem. Also, while in operation it may be worthwhile to check for AC current in the whole cable—use a low-range clip-on ammeter around the shield and shielded pair at the grounded end.

 

[DanDel]

Check for other shield grounds as busbar said. If the problem persists, try grounding the shield at the other end instead(still one end only).

 

[cbarn24050]

Hi, its very unlikely to be pickup, especialy as its intermittent, much more likely to be a bad connection somewhere.