Control panel 3 phase sequence indicators

[dr pepper]

I'm a industrial controls electrican.
Years back when I started this kinda work some control panels had 3 neons on one end, which flashed in sequence, I'm not sure if they just indicated the presence of the 3 phases or actually indicated correct sequence.
Does anyone remember these?, the circuitry was probably simple using just R's & C's, I'd like to re create one maybe a low voltage version with leds, probably ott I was thinking of 3 logic counter dividers to flash leds at much reduced frequency, and reset 2 of them when one phase goes through zero.

 

[KlausST]

Hi

Does anyone remember these?

I´m quite familiar with old instruments .. but to be honest I don´t know what you mean.
Maybe some photo or draft?

I was thinking of 3 logic counter dividers to flash leds

I´d use a microcontroller.

when one phase goes through zer

When one (loaded) phase is missing it usually does not go to zero because of the other phases with loads.

Klaus

 

[Easy peasy]

Are you talking about synchronising two 3 phase systems ? e.g. generator and mains - if so the " 3 lamps " method is very good for checking operation of automatic synch & close systems ...

This is done with one lamp U-U, and the other 2 V-W and W-V

at steady state synch, the U-U is effectively off ( same volts both sides ) and the other two are max brightness.
at near synch if placed in a triangle the light appears to revolve slowly ...

neons showing zero cross will flicker at 100/120Hz - so no earthly use to human eyes ...

 

[BradtheRad]

3-stage chaser or sequencer circuit turns led's on and off. Self-oscillating.
Uses 3 NPN, 3 capacitors, 6 resistors. Low voltage.
(My simulation has 2 led's lit at a time. By mounting led's across transistors you can have 1 led lit at a time.)

www.redcircuits.com/Page72.htm

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Up to 3 neon bulbs arranged in simple chaser circuit. Power supply is 90 VDC.
Uses 3 resistors, 2 capacitors.

www.bowdenshobbycircuits.info/page7.htm#neon.gif

 

[dr pepper]

Never seen them used with gen sets, but I spose you could.
It seems these were not all that popular.

 

[d123]

Hi,

Similar ideas, for LEDs, not thought about details or implemenbility much..., what about dividing down AC phases, and isolating with optocouplers, then:
a) quad comparator, three triggering on zero crossings, fourth resetting other two.
b) three 555s as one-shots triggered by falling edge of sine waves and outputs lasting e.g. 333ms, lighting LEDs momentarily at least, using third 555 to reset the other two maybe, or a bjt with CR on base to deliver short reset signal.

 

[crutschow]

Here's an article that discusses a Neon bulb phase detector (among others).