Decoupling Capacitor to add delay in relay circuit 1

[NGLENGR]

I have a simple relay control system on a machine. A local switch is driven by a 120VAC supply. It appears that this switch sees small transients which can cause it to trip the relay it feeds and cause the machine to trip out.

My question is: How do I size/spec a decoupling capacitor to add a short (say 2-5 second) delay in the reaction of the switch to the relay.

Full disclosure: I am a mechanical engineer and therefore somewhat less wise to circuitry and control than a brick wall.

 

[waross]

It appears that this switch sees small transients which can cause it to trip the relay it feeds and cause the machine to trip out.

Unlikely. Such transients are unlikely on a 120 Volt supply but we need more information. You have to find the cause of the tripping before applying a cure. A capacitor on an AC circuit will go through a "Charge+, Discharge, Charge -, Discharge, every 16.66 mili-seconds. This may address a transient if you have a transient but will not create a 2-5 second delay regardless of size.
Can you post a circuit drawing? What type of switch? Why do you suspect transients?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Your use of the word "trip" has me confused. Tripping is a term generally applied to protective devices. Is this a protective relay you are referring to? Or is it a control relay, and by "trip" you mean activate? or deactivate? Sorry to be so pedantic, but the precise terms mean different things to us that you may not realize.

If referring to a control relay, there are versions called "On-Delay* Timers" that can be set to not change state until a user set time period has elapsed. When used in situations like what I think you are describing, they are called "De-bounce Timers" because they delay activation until a limit switch or float or other mechanical device quits bouncing around.

*Also called "Delay-on-Make", or NOTC for Normally Open, Timed to Close, several other descriptive terms.


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[waross]

In IEC equipment from time to time I see Negative Temperature Co-efficient resistors applied in series with relays or contactors to introduce a small delay on energization.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[NGLENGR]

waross,

I'll try and find a circuit diagram / logic diagram (no promises, the system was built in 1984 and the documentation has grown legs). The trips are due to a level float in an oil sump, it has some jitter to it.

jraef,

That may be exactly what I'm thinking. The switch is normally closed, energized, and when it goes into a bad condition it opens and de-energizes the relay circuit. This in turn trips the machine to prevent it from having damage due to low oil level.

I'll try and find more information on this system so I can pose the question in a better format.

 

[waross]

For this instance I would go with jraef's suggestion for an on delay timer set for a few seconds. lps for Jeff

Bill
--------------------
"Why not the best?"
Jimmy Carter