A magnetic pickup is essentially a coil wound around a permanently magnetized probe. When discrete ferromagnetic objects—such as gear teeth, turbine rotor blades, slotted discs, or shafts with keyways—are passed through the probe's magnetic field, the flux density is modulated. This induces AC voltages in the coil. One complete cycle of voltage is generated for each object passed. If the objects are evenly spaced on a rotating shaft, the total number of cycles will be a measure of the total rotation, and the frequency of the AC voltage will be directly proportional to the rotational speed of the shaft. Output waveform is a function not only of rotational speed, but also of gear-tooth dimensions and spacing, pole-piece diameter, and the air gap between the pickup and the gear-tooth surface.
1. Timing Fluctuations:
testing MPU (Magnetic pickup unit)
2. Magnetic Pickup in the Distributor
The magnetic pickup in MSD Distributors can also be checked with an Ohm meter to make sure it is within operating specifications. Once again, connect the Ohm meter's leads to the two terminals of the pickup. The resistance should be within - 1, ohms.
Every ignition system requires a trigger signal to accurately fire and deliver a high voltage spark from the coil. There are several ways this is achieved, from mechanical breaker points to magnetic pickups, optical triggers and other electronic switches which all serve the same function; to accurately trigger the ignition at the correct moment for the ideal spark timing. MSD Ignition incorporates a magnetic pickup in our distributors because of their reliability and accuracy. In fact, most major automotive manufacturers used magnetic pickups in their distributors until the advent of distributorless ignition systems in late model vehicles. This pickup functions in a similar manner as the magnetic pickup which will be explained below. This bulletin provides an explanation as to the operation of a magnetic pickup and non-magnetic pickup, their polarity and testing along with a few helpful installation tips.