4-20 ma surge suppression 1

[gtwy]

We have a customer who's waste water treatment plant flow metering has become very prone to damage from lightning strikes.
Historically the field installed flow meters were connected to strip chart recorders in the control room w/ very rare storm damage.

In the last year or so they have replaced the recorders w/ G.E. PLC's and a graphics screen. Now it is quite common for lightning to infiltrate the loops and kill the PLC A.I. cards and in some cases the output portion of certain flow meters.

Generally the PLC microprocessors/power supplies and flowmeter microprocessors remain functional, which points me to the 4-20 loops. The loop cable is appropriate and shields terminated properly. Most of my instrument experience lies in large oil refineries where lightning isn't an issue.

Any suggestions on surge suppression for the loops, etc?

 

[djs]

various international companies make surge suppressors for 4-20ma signals. Generally they are rated to 24VDC. Examples are Phoenix Contact, Citel, Dehn, Emerson, MTL etc. Doing a google search for the manufacturer's name should bring up their web page which will lead you to their surge suppressor offerings. Depending where your are select the appropriate manufacturer and find a local distributer.

The current state of the art in this type of surge suppressor is a three stage unit. The first stage is a glass discharge tube, the second stage is an inductor and the third stage is a fast semiconductor voltage limiter of some type. We have employed this type of surge suppressor in west central Florida for many years and they offer almost total protect in the most lighting prone area of the US.

 

[daveross100]

add TVS protectors on the lines ,

daveross100 at gmail dat com