What does a pressure sensor do and what types are there?
Pressure sensors in plants or machines measure the pressure of fluids or gases of all kinds flowing through the systems. A diaphragm as a pressure-sensitive element is the most important component inside the sensors. If the diaphragm is subjected to a pressure impact, it expands. This expansion can be measured precisely and thus the current pressure applied can be calculated.
There are three types of pressure sensors or pressure measurement techniques for accurate pressure measurement:
- Piezoresistive pressure sensors with a special silicium circuit: this is mounted under the diaphragm, surrounded by non-compressible silicone oil. A change in pressure on the membrane causes a measurable change in the electrical resistance in the circuit.
- Piezoelectric pressure sensors are based on the use of a crystal, e.g. quartz, in which a pressure generates a well measurable, proportional electrical charge.
- Capacitive pressure sensors, on the other hand, function like a plate capacitor. They consist of a membrane and a substrate, which act as a hermetically sealed anode and cathode. Pressure on the membrane reduces their spacing and allows electrons to cross over. This produces a measurable change in capacity that corresponds to the change in pressure.
The different techniques each have their own areas of application:
- Piezoresistive pressure sensors are used for measuring static pressures.
- Piezoelectric pressure sensors are optimally suitable for the measurement of dynamic pressures and high static pressures with low pressure fluctuations. They are also used for quasi-static pressures under very high or very low temperatures.
- Capacitive pressure sensors - especially those made of ceramics - are also designed for extreme ambient conditions or aggressive substances.
Ceramic always makes the sensors very robust. For less harsh environmental conditions, however, pressure sensors can just as easily be made of metal or, like our PSC pressure sensors, stainless steel.
Where are pressure sensors used?
The range of applications for these sensors is enormous. At home, for example, they are used to measure water levels in various appliances or in coffee machines. The sensors can be found in medical technology such as respirators or in agricultural machines. Numerous industrial applications can be found in automation processes, hydraulic solutions, cooling systems or robotics.
The sensors are often part of other components such as pressure switches or pressure transducers.
Depending on the design, pressure switches display the pressure values measured by the sensor or trigger a reaction at a certain pressure. For this purpose, our pressure switch TSE3-D provides a display for setting the switching pressures and for displaying the current pressure value and other data. Pressure switches like the TS51 have an intuitive switch point adjustment without display. When the easy to select switching pressures are reached, they trigger a switch-off or switch-on reliably and quickly.
Pressure gauges (also known as pressure transducers or pressure transmitters) continuously provide direct feedback on the measured system pressure with high accuracy. Both absolute and differential pressures can be recorded. Their signal is given via an analog or digital output.
Application examples for pressure sensors
The following examples show specifically where and how pressure sensors work.
Vehicles contain numerous pressure sensors. To allow cars or trucks to drive at all, they need these components, especially on or in their engines. The sensors monitor fuel combustion in the cylinders of the engines.
For optimal running and long durability, the units always need a precisely adjusted supply of fuel. Too little or too much fuel damages the engines, even leading to total failure. To ensure that this does not happen, the engines are equipped with pressure sensors. They measure the pressure in the engine when fuel is supplied. If it deviates from the manufacturer's specified values, they emit a warning signal.
Hydraulic power packs like our mini hydraulic power pack SMA 05 are optionally available with different return filters. In these filters we have installed pressure sensors (or more precisely: differential pressure sensors). By measuring the pressure, the sensors detect the degree of contamination of the filters. This means that you will be informed at any time when a filter that has become too heavily clogged should be replaced quickly and the unit will continue to run trouble-free.
How do you choose the right pressure sensor?
- First, you need to have a look at the type of pressure you are measuring. Is it an absolute pressure, a relative pressure, or a differential pressure? The type of pressure determines the selection, especially with sensor technology.
- To measure an absolute pressure, there is a vacuum on one side of the diaphragm. The diaphragm deformation then corresponds exactly to the measuring pressure.
- To measure a relative pressure, normal air pressure on the relevant side of the diaphragm is sufficient. Its deformation precisely shows the difference between the measured and ambient pressure.
- Differential pressure sensors have two inputs on each side of the diaphragm. Here, the deformation is caused by the pressure difference between the two inputs.
- The very next point to look at is the measuring range of a pressure sensor. It must of course correspond to the existing pressure range. Plan for occasional pressure deviations as well.
- You should also consider the operating temperature. Our pressure sensors work reliably in a fluid temperature range of -20 to +80° C. In this case, the ambient temperature can be up to 50° C.
- Next, the output signal of the sensor or component must match your measurement loops or control loops.
- Finally, pay attention to the configuration of the sensor. The majority of sensors have a thread in different widths for easy installation on pipes or tanks. If needed, you can also find sensors with flanges, for soldering on PCBs or front flush membrane sensors.
The right choice of pressure sensors, other parts and solutions for fluid technology
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