Sensors and Actuators

Sensors and Actuators Off Car Testing

Optical Distributor

One of the tests I did was of the Optical Distributor. This type of distributor uses 2 LEDs, 2 photo diodes and also a Steel plate that passes between them. This plate has a number of openings in it that are used to determine when a signal should be sent to the spark plugs causing them to spark at the correct times in the 4 stroke engine cycle. It in effect times the ignition. The plate interrupts the signal from the LEDs that goes to the photo diodes breaking the signal which breaks the circuit which then prevents the spark plugs from sparking at the wrong times.

Showing the steel plate and openings in it
the sensor part is the black box to right

Testing of a Optical Distributor

Testing Is done by connecting the sensor to a 5V supply and also a ocilliscope. 

• Connect Power to the correct terminals of the plug to distributor. 
• Wire colours: black earth, red power supply, white or green signal out
• Connect 2 1K Pull up resistor in between connectors that go to the ocilliscope and from power supply
• Earth osilliscope probes on body of component
• Turn on supply and scope
• Rotate distributor and read what readings are shown on scope as you turn it

Wiring up of optical distributor

Typical Readings

as distributor is rotated voltage should drop to around .172V and then increase to full voltage 5.24V and then drop again depending on position of the steel plate, and what opening is over the sensor. If it does not do this the distributor is faulty. But before you come to this conclusion make sure it is wired correctly.

Oscilloscope Reading

Shows the various openings and the different readings they show. large gap is for cylinder 1
smaller gap is for the other cylinders and smallest is normal spark operation

Thermo Fan Switch

The Thermo fan switch is used to determine when the fan should be operating during normal driving. It is a type of switch that detects the temperature of the engine coolant, and at a pre determined temperature it sends a signal to the ECU to switch the fan on.

The switch contains a bi-metal strip that is made of 2 different metals that are back to back on a single metal strip. One has a higher temperature that it bends at, to the other metal. As the temperature rises the strip begins to bend to a point where it contacts a terminal in the switch, (this is around 90°C) this then activates the circuit and sends the signal to the ECU to activate the fan.

Testing Of The Component

Switch being tested in water. that is being heated by an element below it

Testing of a thermo fan switch is done using two multimeter's. One is used to measure the temperature of the water and the other is attached to the switch measuring the resistance of the switch, as the water temperature rises.

process: 

1. Connect multimeter to the two wire terminals that come from the switch 
2. Switch the other multimeter onto the temperature setting and put probe of the thermometer into the water
3. Heat the water until the multimeter measuring resistance from switch goes from a reading of 0.3Ω to OL
4. Read the temperature that the switch went to OL and record. This should be 80°C - 90°C if it is under or over this temperature that it switches to OL it would mean that the switch is faulty and would need replacing. 

Readings on Multimeters when switch went to "OL"

If the switch is not switching at the correct time this would cause the engine to overheat and in worse cases seize, because the engine coolant will begin to boil. Hence why the switch activates at 90°C to prevent boiling of the coolant.

Ignition Systems

I also assembled various Ignition systems into working order each one required me to run power into them through a ignition module and then into a coil and a spark plug

Ignition module used in the circuits

Single Coil

This is the basic Ignition system that requires to be run through a single coil and HD lead to spark plug. It also had to be connected to the Ignition module and the function generator to simulate normal operation. The terminals of the module had to be connected to the correct wires to make it work.

Spark in Single coil set up

We also used a distributor with this instead of the function generator. It required a Magnetic inductive distributor to be wired up in place of the function generator and turning by hand to create the circuit. (Below) a ignition module was still used but no function generator was required

Distributor is in bottom left corner 

Video of operation: 

Wasted Spark

This system uses a coil pack which contains two coils. One for each bank of cylinders. So two spark plugs were always in operation. either cylinders 1 and 4 or 2 and 3. This also required use of the ignition module and function generator.

Spark plugs in operation as you can see two are operating at once

COP (Coil On Plug)

This system uses a coil and ignition module that are built into a single unit. There is one of these for each cylinder of the engine. It is the most efficient system and is most commonly used today.

We also made our own Ignition module using Two 2N2222 transistors and a 12Ω resistor it was wired up the same as previous module and was used to operate a single coil ignition system.

Assembled module

Signal wave obtained