How to select R and C?

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gary36

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I have a particular design where timing has to be set from 1s to 90s. I have two options, R=1M(pot) and C=100uf or R=10M(pot) and C=10uf
Which one of the above would be better choice with respect to timing accuracy and long term stability?
 

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Look up the leakage current in the data sheet for the capacitors. Multiply by the corresponding pot resistance.
That is the error voltage you get from the leakage current. The 1MOhm + 100uF option is probably best.
Also consider a higher frequency oscillator with a divider chain for such long delay times.
 

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Which one of the above would be better choice with respect to timing accuracy and long term stability?
Click to expand...

1) What are your goals for accuracy and stability ? Range of T and V effects your environmentals have to
deal with ?

2) What device are you using with these passives to generate delay/timing ?


Regards, Dana.
 

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Accuracy and long term stability can be expected with film capacitors. This limits achievable capacitance values.
There are also timers with analog time programming and frequency divider, e.g. TI TPL5xxx series.
 

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