Sensors Chapter 17 Lesson 3

Computer System Operation There are three stages of computer system operation: input processing and storage output

Inputs and Outputs

Computer System Block Diagram Fig 18

Sensors 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

Some of the sensors located on the engine and transaxle 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

Uses a semiconductor chip that reacts to magnetic fields 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

A reverse-biased photodiode conducts current when exposed to light 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 Manifold absolute pressure sensor (MAP) 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) Engine speed sensor 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) Mass airflow sensor (MAF) 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 Brake switch 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 EGR sensor Impact sensors 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) Fuel tank pressure sensor 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