DI/AI surge protection

rQx

Lifetime Supporting Member
Join Date
Oct 2010
Location
Trelleborg
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1,049
Hi,
Unfamiliar ground here, but a client is asking for surge protection for digital and analog instruments. I did some research on Weidmuller and they had relays for it. But shouldn't a regular interface relay do it (for the digital inputs), or does it have to have more ability to take high voltage?
/Tim
 
What spec's or surge ratings is your customer asking for? Are they worried about surges from incoming power or field wiring ? For incoming power... I would use powers supply's with built in TVS (Transient Voltage Suppression).
The DC output side of power supply should be protected from surges or spikes. Phoenix contact also makes some devices that can help with field wiring protection. If there are other devices in your enclosure that are powered with ac voltages their are ac line filters available to protecting these devices. Most TVS should have a rating to see if it meets your customers needs?
 
surge protection is dependent of the environment like explosion etc, and the working voltage, so yes your client does have a good point.
 
It's the field wiring they are worried about. I saw that pheonix had something for it and it was similar to weidmuller. But this is a more general question, why I need a special relay if I use a regular interface relay for my digital inputs to the cabinet, would the incoming and the internal wiring be seperated if I used a interface relay?
 
When you use the term "regular interface relay"...is this is an isolation relay?
Most digital inputs that I work with are 24vdc inputs. So lets say its a 24vdc control system. Let also assume your field wiring is also 24vdc. The interface relay should be ok as long as your 24vdc power supply for your control and your field wiring are two separate 24vdc supplies. I am also assuming your interface relay has some sort of optical isolation built in? With this being said if its in a manufacturing setting both supplies will still be power by the same incoming AC voltage..so now you must protect this side from spikes which is where the TVS (Transient Voltage suppression) or ac lines filters comes in. I see most spikes come from the AC side of the control system and very few from the field wiring side. I would also consider using quenching diodes on any internal relay coils that do not have them build in. Also make sure all your shielded field wiring cable drain wires are only terminated at the control cabinet side to ground.
 

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