What Is Absolute Pressure?

Absolute pressure refers to the pressure directly acting on the surface of a container or an object, that is, the actual pressure experienced by an object. Its zero point is an absolute vacuum, and the symbol is PABS (ABS is the subscript). The pressure on the earth's surface or surface objects caused by a very thick atmosphere surrounding the earth's surface is called "atmospheric pressure", and its symbol is B;

Absolute pressure refers to the pressure directly acting on the surface of a container or an object, that is, the actual pressure experienced by an object. Its zero point is an absolute vacuum, and the symbol is PABS (ABS is the subscript). The pressure on the earth's surface or surface objects caused by a very thick atmosphere surrounding the earth's surface is called "

There are three ways to express pressure, namely: absolute pressure, gauge pressure, negative pressure or vacuum ^[1]

The legal unit of pressure is Pa (Pa), and some larger units are Megapascal (MPa) = 10 ^ 6Pa

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In practice, a differential pressure transmitter can be used instead of an absolute pressure transmitter to measure absolute pressure.

The intake manifold absolute pressure (MAP) sensor is used to measure the absolute pressure (vacuum) change in the intake manifold and convert it into a voltage signal, which is transmitted to the engine electronic control unit (ECU), and the ECU judges the engine load accordingly. , And combined with the speed signal to determine the fuel injection amount ^[3] .

The intake manifold absolute pressure sensing element consists of a silicon chip. A pressure diaphragm was etched on the silicon chip. There is a piezoresistive strain gauge on the pressure diaphragm to form a Wheatstone bridge. In addition to the pressure diaphragm on the silicon chip, a signal processing circuit is also integrated. The silicon chip and a metal case form a closed reference space. The reference space is evacuated, so its absolute pressure is close to. The pressure on the active side of the silicon chip is approximately, and the back side is the pressure in the intake manifold to be measured. The thickness of the silicon chip is micron, so the change in the pressure of the intake manifold will deform the silicon chip, and the piezoresistor will deform accordingly, and its resistance will change accordingly. After being processed by the signal processing circuit of the silicon chip, a voltage signal having a linear relationship with the pressure is formed. Under standard atmospheric pressure, the signal output voltage of the pressure sensor is close to the power supply voltage. If the power supply voltage is, the signal output voltage of the pressure sensor when the throttle valve is fully open is about.