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# Does anyone know the theory of how a solid state timing relay operates?

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### #1 of 8 OFFLINEGeorge_W_K

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Posted March 10 2003 - 03:03 PM

Hello,

I know that is a strange question, but I need to know for a shop write-up I am doing for my electrical apprenticeship. Our text book explains how a dash-pot timer uses the displacement of fluid to produce a time delay, and how a pnuematic timer displaces air, but it doesn't explain how a solid state timer produces its delay. I cannot find any information anywhere on the net. Can anyone help me?
George

### #2 of 8 OFFLINEKevin P

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Posted March 11 2003 - 12:16 AM

There are probably a number of ways to do it, but two I can think of are: 1. The analog way: Charge (or discharge) a capacitor, then time how long it takes to discharge (or charge) through a resistor. When the capacitor's voltage reaches a certain threshold, the relay triggers. 2. The digital way: A counter starts at some value, and decrements at a fixed rate until it reaches zero. The relay triggers when the counter reaches zero.

### #3 of 8 OFFLINEGeorge_W_K

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Posted March 12 2003 - 05:20 PM

Thanks for the reply, Kevin. That helps me out a lot. Since you said there are more ways to accomplish it, do you know of any more? So when you buy a solid state timing relay, they have capacitors in them? I'll take as much info as I can get. My shop write-up isn't due until a week from this Tuesday. Thanks, again.

### #4 of 8 OFFLINEGrant B

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Posted March 12 2003 - 05:47 PM

You can use just about anything for a timing device, it depends on how much accuracy you need and how much you want to spend. A cap discharge is cheap, easy and fairly easy to impliment. In SW you can do it using clock cycles ...very short cycles easily used in timers. Anything that repeats can be used for timing.
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### #5 of 8 OFFLINEGeorge_W_K

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Posted March 12 2003 - 05:51 PM

Does it make a difference if I mention that my homework is on motor control circuits specifically? Does that change anything I have heard?

If it does, I apologize for leaving out that detail.
If not,

### #6 of 8 OFFLINEGeorge_W_K

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Posted March 23 2003 - 09:55 AM

Kevin and Grant, I just wanted to thank you for your help. I am finishing my write-up today with the info you provided. Regards, George

### #7 of 8 Guest_Eric Kahn_*

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Posted March 23 2003 - 11:33 AM

solid state relay's with time delay also use integrated circuit clocks to control the time delay, we have lots of adjustable ones at work with variable knobs on them

### #8 of 8 OFFLINEGeorge_W_K

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Posted March 23 2003 - 11:49 AM

Thanks Eric, I added that to my report!

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