Silence button with timer

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MetsFan

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Hey guys, please bear with me since I'm an ME trying to figure out circuits.

I'm working on a control panel with a 24V alarm buzzer. The alarm buzzer needs to be silenced for 5-10 minutes at the press of a momentary switch. I looked into time delay relays, but it looks like those are opposite of what I need (output energizes with a trigger). Can time delay relays work the other way as well or do I need to think of a different approach?

Thanks.

 
You should be able to do that with a timer. I've done it before with Crane alarms for silencing actions as you just described. Can be done with using a pneumatic on-delay, held open type timer.

On a side note, doesn't your company employ any EE's? Any openings? LOL ;)

 
Thanks Fox. Nope, no EE's here, we're all mechanical engineers. We do a lot of refrigeration stuff, but we are also responsible for designing control panels and lighting. I've been here a year and a half already and I'm still learning.

 
There are actually many ways you could do this. One is to use an interval timer relay in series with a latched silence button in your 24V circuit. When you press the silence button, it closes the 24V circuit and energizes your interval relay. It will need to be latched so that it holds closed as long as you still have 24V on the circuit.

The output of the interval relay will be a normally closed contact in your buzzer circuit. So when you hit the button and the relay energizes, the contact opens and your buzzer is silenced. However, the interval relay will on keep the output energized for a set amount of time, after which the output will deenergize and the contact will close, making the buzzer sound again.

Usually with these though you'll need to deenergize the input circuit to unlatch your silence button and reset the interval timer. You could do this with a separate "reset" button in your input circuit that opens while pressed and then springs back to closed.

This is just off the top of my head thiuch, and I'm sure there are way more efficient ways of doing it. It's simply the first thing I thought of.

 
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While certainly a PLC could handle it, I'm thinking that will drive up the cost of this particular simple application such that it wouldn't be very economical.

 
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