How the SU63 Speed Pickup Works
The SU63 Speed Pickup is a device designed to be used to sense the speed of turbochargers. A turbocharger rotates very fast – some 10,000 rpm or more, and standard sensing techniques for measuring the speed often fail in the conditions around the vehicle engine. This application note describes how the SU63 senses the very fast turbocharger rotation and how the signal is developed.
The SU63 is simply a coil of wire mounted on a flexible core and with a cable for making the signal connections. The SU63 is completely passive – it does not require power and generates a signal only in the presence of a moving magnetic field.
Here is how the SU63 develops its output signal:
A rotating permanent magnet, whose magnetic field sweeps through the SU63 coil will develop an induced emf that is expressed as a voltage. As the field sweeping the coil changes in strength and direction as a function of the magnet rotation, the voltage generated varies accordingly. The emf signal amplitude is proportional to the rate of change of the magnetic field in the coil.
In practice, a bolt head or nut on the moving shaft of the turbocharger is magnetized by leaving a strong permanent magnet attached to the part over night. The SU63 is placed such that the magnetic field from the part will sweep through the coil as the turbocharger rotates. The closer the coil is to the moving part – and the stronger the magnetic field – the better the voltage signal will be from the SU63.
Of course part of the time the magnetized part will be far enough away from the SU63 so that no signal is developed. But as the part passes by it will generate a kick in the coil that can be counted by electronics connected to the SU63. As the turbocharger spins faster, the signal will decrease in duration but increase in amplitude.
You can view the datasheet and product page of the SU63 here.