Today, not barometers with mercury are used in industry, but quite modern and reliable sensors. Their principle of operation differs depending on the design features. All have both advantages and certain disadvantages. Thanks to the development of electronics, it is possible to realize sensors for measuring pressure on semiconductor elements.
What are electronic sensors?
Electronic pressure sensors for water or any other liquid are devices that allow you to measure parameters and process them with special control and display units. A pressure sensor is a device whose output parameters directly depend on the pressure in the measured place (tank, pipes, etc.). Moreover, they can be used to measure any substance in various aggregate states - liquid, vapor, gaseous.
The need for suchdevices is caused by the fact that almost the entire industry is built on automatic control systems. A person only performs configuration, calibration, maintenance and start-up (stop). Any system works automatically. But such devices are also often used in medicine.
Element design features
Any sensors consist of a sensitive element - it is with its help that the effect on the converter is transmitted. Also in the design there is a circuit for signal processing and a housing. The following types of pressure sensors can be distinguished:
- Piezoelectric.
- Resistive.
- Capacitive.
- Piezo resonant.
- Magnetic (inductive).
- Optoelectronic.
And now let's look at each type of device in more detail.
Resistive elements
These are devices in which the sensing element changes its resistance under the influence of a load. A strain gauge is installed on the sensitive membrane. The membrane bends under pressure, the strain gauges also begin to move. At the same time, their resistance changes. As a result, there is a change in the current strength in the converter circuit.
When stretching the elements of strain gauges, the length increases and the cross-sectional area decreases. The result is an increase in resistance. The reverse process is observed when the elements are compressed. Of course, the resistance changes by thousandths of an ohm, so to catch this, you needput special amplifiers on semiconductors.
Piezoelectric sensors
The piezoelectric element is the basis of the design of the device. When deformation occurs, the piezo element begins to generate a certain signal. The element is installed in the medium whose pressure is to be measured. During operation, the current in the circuit will be directly proportional to the change in pressure.
Such devices have one feature - they do not allow you to track the pressure if it is constant. Therefore, it is used exclusively in the case when the pressure is constantly changing. At a constant value of the measured value, the generation of an electrical impulse will not be performed.
Piezo resonant elements
These elements work a little differently. When voltage is applied, the piezoelectric element deforms. The higher the stress, the greater the deformation. The basis of the device is a resonator plate made of piezoelectric material. It has electrodes on both sides. As soon as voltage is applied to them, the material begins to vibrate. In this case, the plate is bent in one direction or the other. The speed of vibration depends on the frequency of the current that is applied to the electrodes.
But if a force from the outside acts on the plate, then there will be a change in the oscillation frequency of the plate. The electronic air pressure sensor used in automobiles works on this principle. It allows you to evaluate the absolute pressure of the air supplied to the vehicle's fuel system.
Capacitive devices
These devices are the most popular,as they have a simple design, they work stably and are unpretentious in maintenance. The design consists of two electrodes located at a certain distance from each other. It turns out a kind of capacitor. One of its plates is a membrane, pressure (measured) acts on it. As a result, the gap between the plates changes (in proportion to the pressure). From your school physics course, you know that the capacitance of a capacitor depends on the surface area of the plates and the distance between them.
When working in a pressure sensor, only the distance between the plates changes - this is quite enough to measure the parameters. Electronic oil pressure sensors are built exactly according to this scheme. The advantages of this type of structures are obvious - they can work in any environment, even aggressive ones. They are not affected by large temperature differences, electromagnetic waves.
Inductive sensors
The principle of operation is remotely similar to the capacitive ones discussed above. A pressure-sensitive conductive membrane is installed at a certain distance from the magnetic circuit in the shape of the letter Ш (an inductor is wound around it).
When voltage is applied to the coil, a magnetic flux is created. It passes both along the core and through the gap, the conductive membrane. The flow closes, and since the gap has a permeability of about 1000 times less than that of the core, even a tiny change in it leads to proportional fluctuations in the inductance values.
Optoelectronicsensors
They simply detect pressure, have high resolution. They have high sensitivity and thermal stability. They work on the basis of light interference, using a Fabry-Perot interferometer to measure small displacements. Such electronic pressure sensors are extremely rare, but they are quite promising.
The main components of the device:
- Optical transducer crystal.
- Aperture.
- LED.
- Detector (consists of three photodiodes).
Optical Fabi-Perot filters, which have a slight difference in thickness, are attached to two photodiodes. Filters are silicon mirrors with a reflective front surface. They are covered with a layer of silicon oxide, a thin layer of aluminum is applied to the surface. An optical transducer is very similar to a capacitive pressure sensor.
