How can I implement Phase sequence detection in PIC12F508?

How can I implement Phase sequence detection in PIC12F508 ?

How can I implement Phase sequence detection in PIC12F508 ?

I am using PIC12F508 and mikroC PRO PIC. I need to find out the sequence of the 3 Phase inputs. I need to check if Phases are correct (R,Y,B) or not correct (any other phase sequences). How to do that ?

Should I take any one phase as 1st phase and then find out the angle between the other two phases in the order and find out if phases are in sequence like (0, 120, 240) ?

Re: How can I implement Phase sequence detection in PIC12F508 ?

If one phase crossing zero, аnother one has positive voltage, and the last one negative. You don't need the mcu for to detect the phase.

Re: How can I implement Phase sequence detection in PIC12F508 ?

The 12F508 doesn't have an ADC so it's a bit more complicated than sensing the input polarity.

Your method is correct and there are two ways to check the validity of the phases:
1. If you have a neutral or common connection, connect it to VSS and check for the correct time delay using three GPIO pins.
2. If you only have the three phases, wire VSS to one of them and the others to two GPIO pins.

Tip: for simplicity, wire a resistor (~2.2M) between the phase line and GPIO pin, the current will be low enough that the internal protection diodes on the pin will clamp the negative excursion and limit the positive excursion to ~VDD.

The important thing is to measure the delay between phases, using the method above you can just check the delay between one input and the next going high. Do not rely on the presence of an input signal alone as an open circuit phase feed may still register from voltage fed back from the load.

Note that you can not tell which phase is which without some kind of reference back to the power station.

Brian.

Re: How can I implement Phase sequence detection in PIC12F508 ?

Why are you doing this? Phase sequence does not change once you are wired up to the 3-phase power system.
In real life, there are phase-phase shorts (wind on power lines) and loss of one phase that can happen, and lots of noise at zero-cross.
Your firmware should not assume a perfect sequence. Best to debounce each phase and then compare which edge came first, and check for errors from noise/shorts/opens on each phase.

Re: How can I implement Phase sequence detection in PIC12F508 ?

Hi,

Phase order detectors are discussed many times.
Easirider's solution is straigt forward and simple.
For a star point connected meter indeed only two phases are necessary.

Klaus