This time I'm designing a 3-phase signal generator for 50HZ 3 phase tests.
Most of the tests are for amplitude and phase imbalances, and are to be used
in signal stages of protection designs (no 380V involved)
The generator design is discrete, fixed frequency and has provisions for master and independent phase amplitude, phase
shift (with pots) and phase reversal.
I need the phase imbalance detector in order to "zero" every phase channel, and to signal with a led when
any particular phase is outside it´s 120 deg angle.
I though of a method using a 3p full wave rectifier and a comparator, so when a phase is outside it's 120 deg point, a
spike will trip the comparator and probably a flip flop also, signaling the phase imbalance.
The problem that I see with this approach are the characteristics of the rectifier diodes, that may make the circuit trip falsely (or at a
phase imbalance too high to be useful) , the thermal performance of the opamp/comparator, and the impossibility to know which phase was altered.
I 'm going for a discrete approach if possible, that is, no uC or programmables, since I'd like to do the programming on
the "product under test" side.
What do you suggest for this?