3 phase sequencing

[ardhuru]

Hi, here is the requirement;

I need to monitor the 3 mains phases and detect if (a) one goes dead and (b) if the 3 phases are incorrectly sequenced. The 3 phases are being fed to 3 different pins on a 16F676.

The first part seems relatively easy; the second one I'm struggling to find a solutioion for. Am I on the right track here?

The following is for 50 hz;

I plotted the 3 phase waveforms in Excel, to better visualize the timings, and here is what I feel.

If the sequence is correct, the time between 2 corresponding points on adjacent phases would be 10.33 ms; this would be twice that if the wires are incorrectly sequenced.

Now, what makes things complex is that I'd also like to serially be outputtng the 3 readings in a cycle. How can this be done best?

I suspect the easiest solution lies in Darrel's 'Instant Interrupts' article, but I still dont quite get how the logic should be.

Has anyone on the list done something similar?

Thanks for any insight on this.

Regards,

Anand