what is the basic function of an "ENCODER"

[new guy]

I have an escalator handrail SPEED ENCODER. It has a wheel that is held against the handrail and spins when the handrail moves (escalator running). It has 24 volt dc power fed to it through 2 wires one positive and one negative. Then there are 4 other wires that go to an input module. a+ ,a- and b+, b-. This causes input lights to flicker on and off when the machine runs. What should the voltage on the input wires be? Should it be about half of 24v dc? And if viewed on an oscilloscope, should it be a square wave pattern or an ac type sine wave or something else? Basically what should the output of any speed encoder be in general.

[reloadron]

Read this link and note the Output Types. I would guess you have a quadrature type output. If output A leads output B by 90 degrees it denotes one direction if output B leads A by 90 degrees it denotes the opposite direction. Both A & B should put out pulses with one leading the other to determine the direction of wheel rotation. The frequency of the pulses determines the speed.

Ron

[haklesup]

Many encoders are just mechanical switches and thus whatever input voltage you use ends up being the output. However that is not a rule, the 24V could just as well power an LED optocoupler with circuitry to output whatever voltage its designed for. However, 24V would give a lot of noise immunity for an industrial circuit like that so I suspect that will be what you find. The pulse is very ikely a square wave