Hall Effect Sensors

Hall Effect Sensors

A hall effect sensor is a transducer (converts one type of energy to another) which varies in output voltage when magnetic field changes. This sensor has a digital signal.This sensor is generally inside distributors. Some manufactures use it for crank sensors with a special shielding around it to stop dirt ingress.

This consists of a chopper plate which has a fixed firing and dwell time, a magnet and a hall chip. We have 3 wires a power which is normally 5v, some manufactures use 12v. An earth and a signal.

A voltage is applied to the hall chip and a magnet is perpendicular to the face of the crystal conductor (hall chip). Then a small voltage is seen at the edge of the crystal conductor which is called the hall voltage. When the cutter plate cuts the magnetic field, the hall voltages ceases. when the cutter plate moves and theres a gap it lets the magnetic field go across the crystal conductor and we get the hall voltage back again.

There is a integrated circuit (circuit is on the second picture) which switches a transistor on and off to get the signal to ground. The hall voltage goes into a no inverting op amp to turn on the transistor which grounds the signal which is normally 5 v. When the chopper plate is interrupts the magnetic field the hall voltage ceases co there is no voltage at the base of the transistor therfore the sigal can not be grounded. This is how we get a 5v signal and when the chopper plate moves away we have hall voltage which lets the sigaal to ground giving us ov. this is how we get the square wave pattern.

I connected up the distributor to a power supply. Signal was connected to to the oscilloscope. Our distributor was not working properly as the voltages stayed to fluctuated from 2 - 3 volts. We did no get a square wave switching pattern.

I got this pattern from www.picoauto.com. This pattern shows how its switching. the dwell and firing time.When the cutter plate interrupts the magnetic field we have 2.4v and when it moves away we get hall voltage back again which grounds the 2.4v.