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Time delay relay

curious_mind

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I have high reliability hermetically sealed relay and all I have to do is to convert it to a timer relay. I have two questions

1. How do I design high reliability timer circuit?
2. How to make it configurable (say 1 to 60 s )

I do not want to use MCUs
 

barry

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1) How do you define "high reliability"? Is it exposed to radiation? Vibration? Temperature extremes? That's a REALLY vague question.
2) You could use a 555 timer, or any number of other timing devices whose output drives a transistor which then drives the relay coil.
 

andre_teprom

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Hardly achievable unless by using a number of discretes devices and integrated circuits, as 4060, 4017, crystal oscillator, etc...
 

curious_mind

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I meant reliability with respect to temperature (industrial grade) and timing acuracy
 

barry

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You still don't give us anything to go on. What KIND of accuracy? Yoctoseconds?

If an RC (e.g., 555) is not accurate enough, then as Andre says, you're going to need crystals, etc. Or, just buy a time delay relay for about $70USD.
 

d123

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Hi,

I meant reliability with respect to temperature (industrial grade) and timing acuracy
I used to drive myself half-mad looking to get temperature high linearity and 0.1% timing accuracy using assorted typical methods, in the end I accepted reality and feel much better these days.

You could select a high-accuracy timer IC (go pricey or go home), that or get a 1% timing repeatability 555, use a PPS capacitor of as low a value as possible, and go through temperature compensation methods, paying close attention to each part's ppm/°C and a total error budget. It sucks.

1 to 60 seconds range is very hard for accuracy and repeatability of that accuracy - tiny and enormous resistors (some will get warmer than others) or worse, tiny and enormous, drifty capacitors.

I reckon that if 1 second is +-1% accurate, the 60 seconds will be about +-5% accurate, at best.

Good timer ICs are way better than a 555. And laboriously matching diodes to transistor delta Vbes, getting ptc and ntc resistors to offset each other, and other so ons... Best buy a proven part, instead.

Homebrew, loose-ish accuracy tolerance, maybe CD4049UB ring oscillator as slow as possible with smallest timing dielectric capacitor possible, then something like CD4060 but one that has configurable outputs.

I have a homemade 1-second timer for a frequency counter made from SE555s, 100ppm resistors and expensive-ish timing capacitors, open-frame to keep cool, and imho, it's worthless junk, a gleeful newbie error design to be fond of but not use seriously :)
 

d123

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... And trimpots and potentiometers are really useful but generally the component of doom with regard to temperature stability, and for time spent twiddling for (in)accuracy.

This kind of device might be interesting, simple control signal, -20 to +85°C, various options, small-looking solution, supposedly worst-case +-3% timing accuracy; the datasheet shows an application with a relay and load. No idea of price.

KD Series digital countdown off delay or on delay timer
 

andre_teprom

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As other's remarks, a tiny microcontroller could charmly do the job, from a certain level of complexity on, it is no longer worth implementing on a hard circuit due to possibility of realizing the need to add some extra functionality which could be made in few lines of code. I did not spent much time to get introduced and make my first program yet in the last century to be exact. We must honor the semiconductor industry that nowadays brings us a variety of options of microcontrollers of all sizes for all tastes.
 

betwixt

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I agree with Andre on that point. A very inexpensive 8-pin MCU with a built in precision oscillator and an ADC to read the voltage from the timing control can be built in precisely three components, the MCU, a potentiometer to set the delay and a decoupling capacitor. Cost < $2. You might need a transistor and resistor to drive the relay depending on its needs but even the the cost is almost nothing. You should get timing accurate to about 0.5% over a wide temperature range.

Brian.
 

barry

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Yes, a cheap MCU would do it. But, again, if OP only needs one of these then the cost of an off-the-shelf solution versus the cost of design-build-code-test-debug is orders of magnitude cheaper. Unless you work very cheaply.
 

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