Hi folks,
I do quit a bit of work with induction motors configured as SEIG machines (Capacitivly excited) an occasionally just as motor/generators, DOL, that need to be spun up prior to going online. (Small hydroelectric for those of you wondering)
Anyhow...
There is almost always sufficient residual magnetism to get a few volts that will drive a counter but I would like to design something that is opto-isolated and capable of accepting a signal of as little as 500mv and as much as 500V.
The rational is to allow the frequency to be counted with a PLC but to avoid having to have any form of interlocked switch.
Partially because a switch is expensive and cumbersome but mainly because I would like to keep counting the SEIG as its excitation builds.
FYI I use encoder wheels and proximity switches right now and don't even attempt to connect a counting instrument to the output of the machine.
I have in the past used simple transformer, which is fine once the voltage comes up but no us at all when the machine is offline.
I would want two versions of the circuit, one operating at 24VDC, on the control side, and one battery operated to use in conjunction with a multi-meter or similar test equipment. Obviously with appropriately fused/class probes.
I suspect that there is some clever way to do this, and do it safely, and many more ways to blow stuff up and be very unsafe, hence the question.
I am confident that a simple restive divider feeding a clamp circuit, possibly just a zenner, would work but I am equally sure its a very unsafe way to go and have already discounted the idea.
Unless of course such an arrangement could be used to drive an opto-isolator directly... Whats the minimum forward voltage I am likely to find?
Thoughts?
Is there anything commercially available that I am unaware of? Ideally I would want a square wave output with a short pulse every half cycle.
Cheers,
Al
I do quit a bit of work with induction motors configured as SEIG machines (Capacitivly excited) an occasionally just as motor/generators, DOL, that need to be spun up prior to going online. (Small hydroelectric for those of you wondering)
Anyhow...
There is almost always sufficient residual magnetism to get a few volts that will drive a counter but I would like to design something that is opto-isolated and capable of accepting a signal of as little as 500mv and as much as 500V.
The rational is to allow the frequency to be counted with a PLC but to avoid having to have any form of interlocked switch.
Partially because a switch is expensive and cumbersome but mainly because I would like to keep counting the SEIG as its excitation builds.
FYI I use encoder wheels and proximity switches right now and don't even attempt to connect a counting instrument to the output of the machine.
I have in the past used simple transformer, which is fine once the voltage comes up but no us at all when the machine is offline.
I would want two versions of the circuit, one operating at 24VDC, on the control side, and one battery operated to use in conjunction with a multi-meter or similar test equipment. Obviously with appropriately fused/class probes.
I suspect that there is some clever way to do this, and do it safely, and many more ways to blow stuff up and be very unsafe, hence the question.
I am confident that a simple restive divider feeding a clamp circuit, possibly just a zenner, would work but I am equally sure its a very unsafe way to go and have already discounted the idea.
Unless of course such an arrangement could be used to drive an opto-isolator directly... Whats the minimum forward voltage I am likely to find?
Thoughts?
Is there anything commercially available that I am unaware of? Ideally I would want a square wave output with a short pulse every half cycle.
Cheers,
Al