|On Sun, 21 Mar 1999 12:21:45 +0500 "Hashmani" <super.net.pk> hash1
>it will be trip the main contactor if the sequence of phase is not
>save from reverse motor operation, All phases will be looked for under
>voltage, over voltage and for correct frequency,
It seems like a PIC with ADC would be good for this. Rapidly take
samples of the 3 phases and find the peak values. Compare these values
to see if the voltage is in range, and look at the order in which they
are reached to check the sequence. The software should ignore short
pulses of noise (one reading way out of line from the others). RC
lowpass filters externally could do the same thing, they should be
identical for all 3 phases.
>I want to do some isolation between my circuit and phase line as well
It may be easier to put the PIC on the "hot" side, directly connected to
the line. Then isolate the output of the circuit with a relay or
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I dunno guys...again, depends on how critical this is. There are several
rather inexpensive 3phase detect relays out there. Syrlec makes one,
probably others. I've learned over the past several years that sometimes it
makes sense to get something off the shelf. It all depends on how critical
the app is. If I had a $500 motor I was protecting, along with other stuff,
adding $25 for a relay is lost in the noise...
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