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Pressure sensor definition
2016-01-20

A pressure sensor is part of the pressure gauges, which transform as the first link in a chain measuring the physical quantity pressure (force per unit area) into an electrical output as a measure of the pressure. The SI unit for pressure is Pascal with the unit symbol Pa. According to DIN 1301 is also the bar, bar unit symbols allowed. Pressure sensors, it is to measure the steady pressure, a pressure difference or pressure fluctuations until the sound pressure.

There are a number of different pressure sensors on the market, such as: Passive Pressure Sensors, Relative pressure sensors, Absolute pressure sensors, Differential pressure sensors, Piezoresistive Pressure Sensor.

Of the manufacturers, particularly in English-speaking world, absolute pressure sensors with "absolute" or "a" are known. Pressure sensors which are determined for measurements of pressures relative to atmospheric pressure, are referred to as "gauge" or "g". Here one differentiates between trapped (and thus constructively sealed) atmosphere of eg 1013 mbar (sealed gauge) and a measurement relative to the current atmospheric pressure actually existing. In the latter pressure sensors, the atmospheric chamber is usually coupled through a small hole with the atmospheric pressure. Pressures can be measured as the force-transmitting component in gaseous and liquid media, as well as solids.

To capture the measure of measuring various physical effects are used. Therefore, one divides the pressure sensors in the following types:
THe piezoresistive pressure sensor comprises a membrane with applied electrical resistance and is mainly produced as a silicon pressure sensor. Using a pressure-dependent deformation of the membrane and it diffused deformation-dependent resistors in the formation of an electrical voltage. These pressure sensors are inexpensive to manufacture and have a comparatively high sensitivity. While showing the materials used for pressure measurements a strong temperature dependence, but since this is the same effect on the odds, it can be rendered ineffective by a difference-forming electrical circuit.

A piezoelectric pressure sensor In a piezoelectric sensor is produced by means of pressure by charge separation, an electric voltage in a crystal. This is called the piezoelectric effect. Move by pressure in the interior of the crystal ions, resulting in proportional forms on the surface electric charge to the force. The charge is converted by a charge amplifier into a proportional electrical voltage. The direct measurement of the voltage is not possible because the small charge produced to be very well insulated and have experienced no change in electrical capacitance must. Any print can be derivative (short circuit) can be set as the zero point of charge of the charge amplifier, thus eliminating pressure changes directly measurable.

Piezoelectric sensors measure forces in principle only. The sensor should be used in the pressure measurement, has to be reached through a membrane, the pressure proportionally converts into a force.

Advantages of piezoelectric sensors: insensitive to high temperatures; no external power supply required; high sensitivity; mechanically very rigid, making it only slightly comes to natural oscillations or Nachschwingeffekten; kHz for pressure fluctuations at high frequency suitable 100.

Disadvantages of piezoelectric sensors: not be used without charge amplifier; for static measurements such as water or air pressure is not used, because even with a full insulation is a constant charge actually flows in the course of hours.

Pressure sensors in the vacuum region is referred to here
Thermal conductivity according to Pirani vacuum gauge, range 100 ... 0.1 Pa
Ionization gauge Cold cathode Penning after, range about 10-1 ... 10-5 Pa
Hot cathode ionization gauge with Bayard-Alpert, range about 10-1 ... 10-10 Pa

Frequency analog pressure sensor This is mostly a piezoresistive pressure sensor that measures the pressure is by means of strain gauges and expanded to a ring oscillator circuitry. By varying the pressure changes the resistance of the strain gauge and as a result, the frequency of the ring oscillator detuned. The output frequency is directly proportional to the applied pressure.
Pressure sensor with Hall element It operates on the Hall effect, is changed under pressure wherein the magnetic field around the Hall element.

Capacitive pressure sensors, capacitive pressure sensors contain two diffused into a silicon chip capacitors. When pressure is applied, the distances of a membrane on both sides to two opposing capacitor plates and thus modifies the capacitances of the capacitors in opposite directions. Mostly the capacitors part of an internal amplifier whose output signal from the difference of the capacitances dependent.

Inductive pressure sensor Inductive pressure sensors use an inductive displacement transducer, which is associated with a membrane. Pressure changes produce a force on the membrane and move it. As a result, the position of an armature iron varies in opposite directions in two coils: In one increases the inductance, in others they fall. The difference can be determined very accurately electrically. This arrangement can also be replaced by a differential transformer.

Additional sensors for the detection of small pressure fluctuations that occur when sound pressure are listed further measured effects and their applications in sensors of the microphone under the corresponding keyword.