Sensors Chapter 17 Lesson 3 There are three

Sensors Chapter 17 Lesson 3

• There are three stages of computer system operation: – input – processing and storage – output

Inputs and Outputs

Computer System Block Diagram Fig 18

• Most vehicle sensors, or transducers, change a physical condition into an electrical signal • Transduce: – to change from one form to another

Sensor Locations • Sensors can be found almost anywhere on a vehicle: – on the engine – on or in the transmission or transaxle – in the exhaust system – on the wheel hubs – on and in the fuel tank – on the suspension – in the trunk

Sensor Locations Some of the sensors located on the engine and transaxle

Sensor Classifications • Sensors can be classified into two general categories: – active sensors – passive sensors

Active Sensor • Produces its own voltage signal internally • The signal is fed to the computer for analysis • Shielded wire may be used to block induced voltage and interference in the signal wire(s)

Active Sensor

Passive Sensor • Variable resistance sensor • Voltage is fed to the sensor from the computer • Sensor resistance varies with changes in a condition – temperature, pressure, motion, etc • As sensor resistance changes, the voltage signal sent back to the computer changes

Passive Sensor

Types of Sensors

Variable Resistor Sensor • Changes its resistance with a change in condition – temperature, pressure, etc • Throttle position and temperature sensors are variable resistance sensors

Switching Sensor • Opens or closes the sensor circuit to provide an electrical signal • Used to detect almost any condition • Produces a digital signal • Transmission pressure switches are switching sensors

Magnetic Sensor • Also called a permanent magnet (PM) generator • Uses part movement and induced current to produce a signal • Produces an analog signal • Used to monitor speed or part rotation • Vehicle speed and wheel speed sensors are often magnetic sensors

Hall-Effect Sensor • Uses a special semiconductor chip to sense part movement and speed • Produces a digital signal • Applications: – crankshaft position sensors – camshaft position sensors – distributor pickup devices

Hall-Effect Sensor Uses a semiconductor chip that reacts to magnetic fields

Optical Sensor • Uses light-emitting diodes and photo diodes to produce a digital signal • Used to sense part rotation and speed • Used in some distributors and as speed sensors mounted outside the speedometer

Optical Sensor A reverse-biased photodiode conducts current when exposed to light

Piezoelectric Sensor • Generates voltage from a physical shock or motion • An internal crystal produces a voltage signal proportional to the amount of vibration detected • Used to sense abnormal engine vibration caused by engine knock – knock sensor

Piezoelectric Sensor

Solar Sensor • Converts sunlight directly into an electrical signal • Made of a semiconductor material that converts photons into direct current

Solar Sensor

Direction Sensor • Detects the polarity of a moving magnet • Signals which direction a part is rotating • Used in some computer-controlled steering systems

Reference Voltage • Applied to a passive sensor by the computer • 5 volts on most vehicles • The computer steps down battery voltage so that a smooth, constant supply of dc voltage is fed to the sensor • The sensor changes its internal resistance to alter the reference voltage

Sensor Types • Common sensors used in late-model vehicles: • Intake air temperature sensor (IAT) – measures the temperature of intake air as it enters the intake manifold • Engine coolant temperature sensor (ECT) – measures the temperature of engine coolant

Sensor Types • Oxygen sensors – measure the amount of oxygen in the engine’s exhaust gases • Manifold absolute pressure sensor (MAP) – measures pressure inside the intake manifold • Barometric pressure sensor (BARO) – measures the outside air pressure

Sensor Types • Throttle position sensor (TP) – measures the opening angle of the throttle valves to detect driver power demand • Engine speed sensor – measures engine rpm • Crankshaft position sensor (CKP) – measures crankshaft position and speed

Sensor Types • Camshaft position sensor (CMP) – measures camshaft position and rotation • Mass airflow sensor (MAF) – measures the amount of intake air flowing into the engine • Knock sensor (KS) – detects engine pinging, preignition, or detonation

Sensor Types • Transaxle/transmission sensor – checks transaxle or transmission gear selection • Brake switch – detects brake pedal application • Wheel speed sensor – measures wheel rotational speed for anti-lock brake and traction control application

Sensor Types • Oil level sensor – measures the amount of oil in the engine oil pan • EGR sensor – measures the position of the exhaust gas recirculation valve pintle • Impact sensors – detect a collision

Sensor Types • Vehicle speed sensor (VSS) – measures the vehicle’s road speed • Fuel tank pressure sensor – measures fuel tank pressure as part of some evaporative emission control systems • Battery temperature sensor – monitors battery temperature so the computer can adjust charging system output as needed

Circuit Sensing • Involves using the computer itself to monitor component and circuit operation • Computer monitors current flow through various circuits to diagnose: – fuel injectors – ignition coil action – computer operation