Phase Comparator

When cleaning out an old shed/workshop, I came across a phase comparator made by Pfisterer. This is a hand held unit and may be for use on HV systems judging by the
look of the leads and looks hardly used. Could anyone tell me what these instruments are for and what the value might be.
TIA
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might
One stage of a phase locked loop?
Use it to put 2 generators in phase and keep them in sync by using an error voltage as a control.
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----------------------------

-------------- Possibly a device to check phase sequence prior to making connections. At one time there were rotating disc models and later there were devices with lamps- neon originally but now likely to be LED's
--

Don Kelly snipped-for-privacy@shawcross.ca
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Thirty years ago I was asked to update a phase-rotation sensor for mainframes (their phase-controlled power supplies didn't like to be plugged in backwards and backwards blowers didn't work well ;). LEDs don't work so well in this application. They use a lot of current at a low voltage (low impedance), thus load/upset a phase delay circuit. The answer was a 'D' flipflop on a bridge between the phases. That was sensitive to zero-crossing distortion, but a solvable problem.
--
Keith

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