Variable Reluctance Transducers (VRT or simply reluctor) – this kind of sensor produces a sine wave output. Generally a VRT sensor will have only 2 wires (a third wire may be present but its generally a shield wire to help protect the signal from "noise").
VRT sensors DO NOT require a power supply, they will have a signal wire and a ground wire only. The way they work is almost the opposite of an electric motor with only one brush where the sensor has a magnet inside with a coil of wire wrapped around it. As a ferrous material passes by the magnet the magnetic field is disrupted and a voltage spike is created in the coiled wires surrounding the magnet, producing a sine wave. This signal is what is fed into the ECU. The ECU cannot interpret a sine wave directly and must first process the sine wave into a digital signal before it is able to use this information. The part of the ECU hardware that conditions the reluctor signal is called a reluctor adapter. It converts the reluctor signals shown above into a square waveform similar to that of the Hall effect trigger. The reluctor adapter and its tuning is dealt with in detail further later on.