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Making Sense of Sensors: Part 1
| There are a lot of things going on in your engine as you drive. A lot of information is taken in and processed. But how is this information gathered and what happens to it once it's collected? |
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Since a computer doesn't have hands, eyes, ears or noses they need to get information some how. That's where sensors come in. These sensors are the eyes and ears of the ECU. As the information comes in, the ECU processes it and determines what output to use to do something.
Here are some of these input sensors and how they work.
Mass Air Flow Sensor (MAF)
The mass airflow sensor is placed in the stream of intake air. It measures the intake flow rate by measuring a part of the entire intake flow. It consists of a hot wire that is supplied with electric current from the ECM. The temperature of the hot wire is controlled by the ECM a certain amount. The heat generated by the hot wire is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to maintain the temperature of the hot wire as airflow increases. The ECM detects the airflow by means of this current change.
Intake Air Temperature sensor (IAT)
The intake air temperature sensor is mounted to the air duct housing. The sensor detects intake air temperature and transmits a signal to the ECM. The temperature-sensing unit uses a thermistor that is sensitive to the change in temperature. Electrical resistance of the thermistor decreases in response to the temperature rise.
Camshaft (or Crankshaft) Position Sensor (CPS)
The camshaft position sensor monitors engine speed and piston position. These input signals to the ECM are used to control fuel injection, ignition timing and other functions. The camshaft position sensor has a rotor plate and a wave-forming circuit. The rotor plate has 360 slits for a 1°(POS) signal and 6 slits for a 120°(REF) signal. The wave-forming circuit consists of Light Emitting Diodes (LED) and photo diodes. The rotor plate is positioned between the LED and the photo diode. The LED transmits light to the photo diode. As the rotor plate turns, the slits cut the light to generate rough-shaped pulses. These pulses are converted into on-off signals by the wave-forming circuit and sent to the ECM.
Coolant Temperature Sensor (CTS)
The engine coolant temperature sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the ECM. The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor that is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases.
Knock Sensor
The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is sensed as vibrational pressure. This pressure is converted into a voltage signal and sent to the ECM.
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