Anand,

if you compare together they may not be the same and
you will end up an error. This is what I would do.
connect all 3 phases thru optoisolater and mux connect
to pic CCP input and capture the speed.

1. select first phase capture and save it
2. do same thing on all other 2 

now you have 3 variables that you can decide what to do
with them. they may or may not be exact same values but
will be very close.

Andre Abelian



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Anand Dhuru
Sent: Friday, January 05, 2007 8:32 AM
To: Piclist
Subject: [PIC]: Phase failure detection




Hi folks,

I am building a circuit that needs to monitor the 3 phases in the mains, and 
detect if (a) any one phase fails, and (b) if the phases are connected 
improperly.

After some search I found 
http://www.picbasic.org/forum/archiv...hp/t-2134.html to be pretty close to 
what I need.

What would be the best way to go about it?

Would this logic work?

Detect positive edge on phase 1
Start Timer 0
Detect positive edge on phase 2
Read Timer 0 as variable 1
Detect positive edge on phase 3
Read Timer 0 as variable 2
Stop + Reset timer
If Variable 1 is equal to (almost) = (Variable 2)/2 = 6.67 ms (for 50 hz) 
then all is ok.

Start again.

Am I on the right track, or is there a better/easier way to do this?

Regards,

Anand 

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