It doesn't work that simply, most of the sensors are fed with a 5 volt refference feed, then return a signal, according to how often activated, which isn't a lot in the case of cps, it would never even reach 5 volt, and would be a AC current, not true ac, as it would be only altering in on off state, being a square waveform signal.
In english it will give out a on/off signal, which is too fast to be captured on most digi metres anyway.
The fact that you are getting a signal at all shows it to be working, as they either do or don't, it uses the disturbance of the return signal wire as the refference, the disturbance being caused by the voltage induced when the relevant point passes the sensor, and temporarily "bridges"(electrically not physically) the signal and feed together.
tabetha
tabetha