AutoPartDex
.com
***New & Used Parts***
AutoPartDex's Catalog
- SuperCenter - Free Search -

ultimate autopart search for every part available


Making Sense out of Sensors
autopartdex.com MAKING SENSE OUT OF SENSORS

The sensors are the onboard computer system's eyes and ears that keep it informed about what's going on. The computer needs accurate information from its sensors so it can make the correct decisions regarding the operation of the fuel system, ignition timing, emission controls, torque converter lockup and other control functions. The number, type and location of the sensors that AC DC Voltage Sensor are used will vary depending on the vehicle application:

The various types of engine sensors can be grouped into the following categories:

VARIABLE RESISTANCE SENSORS
Often called "2-wire" sensors because they are usually connected by two wires to the computer; a signal return wire and a ground wire. Variable resistance sensors include coolant temperature (CTS) sensors, manifold air temperature (MAT) sensors, and outside air temperature (OAT) sensors.

VARIABLE VOLTAGE SENSORS
Often called "3-wire" sensors because they are connected to the computer with three wires; a voltage supply wire (usually 5 volts), a signal return wire and a ground wire. Variable voltage sensors include throttle position (TPS) sensors, manifold absolute pressure (MAP) sensors, barometric pressure (BARO) sensors and some mass airflow (MAF) sensors.

An oxygen sensor also produces a variable voltage signal, but unlike other sensors in this category an oxygen sensor generates its own voltage like a battery. The voltage produced by the sensor depends on the amount of oxygen in the exhaust. The lower the oxygen level in the exhaust, the higher its output voltage. The sensor's output voltage ranges from about 0.1V (lean) to 1.0V (rich). The O2 sensor may have one, two or three wires connecting it to the computer depending on if it is the heated variety or not.

Magnetic Crank Shaft Sensor FREQUENCY SENSORS
These sensors contain electronics that convert their output voltage into a pulsating signal. The rate or frequency of the signal is proportional to the value being measured. GM uses a variable frequency sensor to measure mass air flow on certain applications. Ford uses variable frequency MAP and BARO sensors on some applications.

A knock sensor also generates a frequency-type signal. It generates a random frequency signal when it detects engine vibrations that accompany detonation. When the computer receives a signal from the knock sensor, it momentarily retards ignition timing until the detonation stops.

VARIABLE RELUCTANCE OR MAGNETIC SENSORS
These sensors use a magnetic pickup to produce a signal. Certain sensors contain a coil wound around a small magnet. These include cam and crank position sensors as well as vehicle speed sensors and ABS wheel speed sensors.

When a notch, pin or hole in a timing wheel moves past the sensor, it causes a change in the magnetic flux field around the sensor. The sudden field change induces an electrical current in the coil, which is then converted to a voltage signal by electronic circuitry connected to the sensor. The induced current that's created in the sensor by the passage of the timing notch, pin or hole first flows one direction then reverses direction as the magnetic field returns to normal. The result is an alternating current (AC) voltage that reverses polarity and crosses zero as it reverses. This signal can then be used by the onboard computer for precise ignition timing as well as injector Oxygen Sensor timing in engines with sequential fuel injection.

Other types of magnetic sensors have a wire coil wrapped around a nonmagnetic "pole piece," as is the case with certain electronic ignition pickups. With these types of sensors, the moving element (the reluctor or star wheel in the distributor) is magnetic. When the magnet moves past the tip of the sensor's pole piece, the changing magnetic field induces an alternating current in the sensor which is then converted to a signal electronically the same as above.

Copyright 2007 autopartdex.com. All Rights Reserved.