Ignition Systems page 7Ignition Systems page 7

Trigger systemsTrigger systems

We have already described the We have already described the contact breaker points, and contact breaker points, and stated that the mechanical stated that the mechanical

system has a limited life span, system has a limited life span, doesn’t stay accurately adjusted doesn’t stay accurately adjusted

for a long time, and that the for a long time, and that the secondary voltage output is secondary voltage output is

limited. limited.

A major improvement in A major improvement in switching the primary circuit is switching the primary circuit is using transistorized system. using transistorized system.

A transistor is used in A transistor is used in conjunction with some form of conjunction with some form of pulse generator to provide the pulse generator to provide the

timing signal.timing signal.

Name the three main types of pulse Name the three main types of pulse generator:generator:

• Hall Effect

• Inductive

• Optical

Label the inductive pulse generator Label the inductive pulse generator

Iron rotor trigger wheel

Path of magnetic field

Air gap (0.5mm)

Permanent magnet

Alternating current generated

Describe the operation of the inductive pulse Describe the operation of the inductive pulse generator trigger system.generator trigger system.

As the iron rotor turns an AC voltage is induced into the inductive winding. The faster the rotor turns, the higher the frequency and the voltage. The voltage and frequency variation provides the sensing signal.

Another of the main types of pulse generator Another of the main types of pulse generator is the Hall Effect, label the illustration below is the Hall Effect, label the illustration below

Rotor arm

Vanes Magnet

Hall chip

Briefly describe its operation Briefly describe its operation

• As the vane passes between the magnet and the hall chip, the magnetic flux is diverted away from the chip. This causes the chip to be turned off and on.

• Note: the spark occurs the instant the vane leaves the air gap.

Questions Questions

1. Name three types of pulse generator.2. How does the inductive pulse generator

work?3. What type of signal does an inductive

sensor produce?4. Why should you be careful when working

on a hall effect system?5. What happens to the signal produced by

an inductive sensor with speed?

Answers Answers

1. Inductive, Hall effect, Optical2. An iron magnet rotor turns and induces

an AC voltage into windings wound around a second permanent magnet.

3. AC current or alternating current.4. A high voltage can be produced by the

coil – even when the engine is being turned over by hand.

5. The frequency increases, the voltage output increases