Electrically, the injector consists of a coil. When a current flows
through the coil, the core is magnetised. This draws the injector
needle into the core of the coil, and the fuel is injected. The
injector coil has a high or low impedance. High impedance injectors
have a coil with a resistance of about 15 ohm. During the time the
injector is activated, a current of about 0,75 A passes through
Low impedance injectors have a resistance of about 1 to 2 ohm. Low impedance injectors can be switched on in two different ways:
- With a series resistor.
- By means of a constant current limiting circuit in the control unit.
Three oscilloscope images are shown below.