Just as I suspected :(

Andre's suggestion would be fine to check basic health of the phases, but 
would not indicate a wrong sequence, and/or would also get fooled by a phase 
signal 'manifesting' itself on another weak / dead phase. I recollect Russel 
had explained this phenomenon in some detail a while back.

In which case, would not my original concept as described in the first post 
be the best approach? Or are there pitfalls here too?

Regards,

Anand


----- Original Message ----- 
From: "Steve Smith" <xygax@blueyonder.co.uk>
To: "'Microcontroller discussion list - Public.'" <piclist@mit.edu>
Sent: Saturday, January 06, 2007 1:06 PM
Subject: RE: [PIC]: Phase failure detection


> Ahh but just checking the period doesn't reveal the direction of rotation
> only that by comparison they are all there.
>
> There is another complication caused by the real world if the supply is
> taken via a delta / star transformer and a motor is connected to the
> secondary you are monitoring, a failure in the primary supply will not
> change the period only the voltage (of two phases)as the motor will 
> continue
> to run and help reinstate the third phase.
>
> It maybe necessary to monitor the voltage using a voltage sensing
> arrangement depending upon application. You have to do this in a UPS to
> ensure correct operation of the static switch under failure conditions.
>
> Regards Steve
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf 
> Of
> Andre Abelian
> Sent: 05 January 2007 18:07
> To: Microcontroller discussion list - Public.
> Subject: RE: [PIC]: Phase failure detection
>
> 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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