Piezo Resistive

A piezo resistive sensor is a resistor circuit constructed on a thin silicon wafer. Physically flexing or distorting the wafer a small amount changes its resistance. This type of sensor is usually used as a pressure sensing device such as a manifold pressure sensor, although it may also be used to measure force or flex in an object such as the deceleration sensor located in the SRS air bag center sensor.

One of the most important piezo resistive sensors is the manifold pressure sensor which monitors the air intake volume for Electronic Fuel Injection (EFI). The signal it sends to the ECU determines the basic fuel injection duration and ignition advance angle.

Within the sensor is a silicon chip combined with a vacuum chamber. One side of the chip is exposed to the intake manifold pressure and the other side to the internal perfect vacuum in the chamber.

A change in the intake manifold pressure causes the shape of the silicon chip to change, with the resistance value of the chip fluctuating in relation to the degree of deformation. An integrated circuit converts the fluctuation to a voltage signal that is sent to the ECU, where the air-fuel ratio is regulated. The sensor has three external terminals: one for power, one for ground and one to provide the voltage signal to the computer. The voltage signal varies with the pressure in the intake manifold.

Another use for this same type of sensor is to sense turbocharger boost. On turbocharged engines, the sensor is used to measure pressures that are higher than atmospheric pressure and to supply corresponding voltage signals to the ECU. To prevent engine damage, the ECU can cut off the fuel being injected if the manifold pressure becomes too high.

INTAKE MANIFOLD PRESSURE SENSOR

Silicon chip

INTAKE MANIFOLD PRESSURE SENSOR

Silicon chip

VOLTAGE GENERATING SENSORS

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