Knock Sensor
The above diagram is a picture of a knock sensor, The crocodile clips in the picture are from an oscilloscope so i could see the voltage frequency the sensor produces which i will get into further in the blog.
The knock sensor is commonly found bolted into the cylinder block wall but some on the cylinder block wall.
Depending on the manufacture the sensor will be located according to where it would operate most effective.
The sensor is there to pick up vibrations in the engine and send that information to the electronic control unit (ECU)and in doing so the ECU will take the information and will change the operation of the spark in the combustion chamber to suit the engine's performance.
The knock sensor has a piezo electric crystalline element inside of it and a resonating plate. The plate sends the vibrations to crystalline element which generates a small voltage. The voltage created by the sensor is then sent to the ECU. Depending on the knock inside the combustion chamber will determine the voltage created by the knock sensor and the amount of voltage.
The above diagram is a image of an oscilloscope screen showing an analogue frequency.
The above signal shows the voltage generated by a knock sensor with a single knock against the table.
Each square represents 100mv.
The above diagram is a picture of a 6speed optical distributor.
In this component it has a Light Emitting Diode, Photo cell and a slotted disc also called a beam interrupter.
The optical sensor will generate a voltage when the LED passes a light on to the photocell, this happens during the rotation of the slotted disc when the light can pass through the disc onto the photocell. when the light is blocked there is no voltage generated.
When light passes through one of the slots in the disc, the voltage generated is then sent to the electronic control module which then determines the ignition timing.
The above diagram is an oscilloscope showing a digital frequency.
this is the digital signal of the optical distributor. As you can see it has 6 different voltage surges which indicates a 6speed optical sensor. each square represents 2volts so when light passes on to the photocell and creates a voltage it generates just above 4volts and also you can see one of the signals has a larger gap and that is because on the rotating disc it has one larger slot than the others which signals that it is at number 1 cylinder.
The above diagram is a picture of a hall effect distributor. Like the optical distributor it sends information to the computer about the position of the engine and to let the computer know when to fire a spark in the combustion chamber. but it sends the message to the computer in the different way. As the optical used LED's and photocells to generate a voltage the Hall Effect distributor replaces the rotating slotted disc with a steel chopper plate. And just like the optical, It creates a signal as the plate spins. This signal is created by a magnet under the distributor cap. Every time the plate passes the magnet it creates a magnetic field but when the field is broken it sends a signal to the computer indicating it is time to fire or the cylinder is at before top dead center.
The above diagram shows picture of a throttle position sensor. This is an on off switch type throttle position sensor.This sensor sends a message to the ECU if you a pressing your foot down on the accelerator or decelerating. The ECU will take the information and determine how much air/fuel mixture the car requires to operate at the driver demand. The on-ff type sensor has a three different terminals, a power switch an idle switch and an earth. So i tested the TPS using a multimeter to find out how it operates.
i connected the multimeter black lead to the earth terminal and the red lead to the idle switch of the TPS. And as the throttle was closed i got a voltage reading but went to 0volts after roughly 1.5 degrees and when i placed the red lead of the multimeter on the power switch i gt no voltage reading when it was closed but around 70 degrees of opening i got a sudden surge of voltage. At idle there is a complete circuit as the contacts a touching causing a complete circuit. But after roughly 1.5 degrees voltage goes to earth as the contacts disconnect and change positions.
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