The reason why it was actually necessary to use four inductive pickups connected in row, can probably only be explained by the fact that the construction - which was one of the first non-contact ignition triggers - had to fit into a distributor. If one then also assumes a maximum of over 3000 RPM, this may be the explanation. Apart from that, the switching devices were not yet as hightly developed as they are today. They needed a high amplitude and an almost vertical zero passage to trigger the ignition.
Four coils switched one after the other are arranged thus, that in a particular position, they align with the points of the central rotor. The rotor has the same amount of teeth as there are cylinders in the engine. The permanent magnets behind it build up a magnetic field. If the rotor rotates, an AC voltage is generated in the coils. From this, the switching device generates a square-wave signal for the triggering of the ignition.
Test- and measuring conditions in a TZI-system
The inductive pickup consists primarily of a coil and it may be measured by using an Ohm-meter.
When starting and while running, a sinus-shaped voltage must be measurable on both pins of the distributor plug or even better, on the control device.
Throughflow, mass, and plus-circuit measurements on the leads can be carried out with the help of an Ohm-meter.