Today, mercury barometers are not used in industry, but rather modern and reliable sensors. Their working principle differs depending on the design features. Everyone has both advantages and certain disadvantages. Thanks to the development of electronics, it is possible to implement 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 such a device in which the output parameters directly depend on what pressure in the measured place (capacity, pipes, etc.). Moreover, with their help it is possible to measure any substance in various states of aggregation - liquid, vaporous, gaseous.
The need for such devices is due to the fact that almost the entire industry is built on automatic control systems. A person carries out only adjustment, calibration, maintenance and start (stop). The operation of any system occurs automatically. But still such devices are often used in medicine.
Features of the design of elements
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.
- Piezoresonance.
- Magnetic (inductive).
- Optoelectronic.
Now consider each type of device in more detail.
Resistive elements
These are devices in which the sensitive element changes its resistance under the influence of the 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, a change in the current strength occurs in the converter circuit.
When tensile strain gauge elements are stretched, the length increases and the cross-sectional area decreases. As a result, an increase in resistance. The reverse process is observed during the compression of elements. Of course, resistance changes by thousandths of Ohm, therefore, to catch this, you need to put special amplifiers on semiconductors.
Piezoelectric sensors
The piezoelectric element is the basis for the design of the device. When a deformation occurs, the piezoelectric element begins to generate a specific signal. The element is installed in the medium, the pressure of which must 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 pressure, if it is constant. Therefore, it is used exclusively in cases where the pressure is constantly changing. With a constant value of the measured value, an electric pulse will not be generated.
Piezoresonance Elements
These elements work a little differently. When voltage is applied, the piezoelectric element is deformed. The higher the stress, the stronger the deformation. The basis of the device is a resonator plate made of a piezoelectric. She has electrodes on both sides. As soon as voltage is applied to them, the material begins to vibrate. In this case, the plate bends in one direction or the other. The speed of vibration depends on the frequency of the current that is supplied to the electrodes.
But if external force acts on the plate, then a change in the oscillation frequency of the plate will occur. The electronic air pressure sensor used in automobiles works by this principle. It allows you to evaluate the absolute pressure of the air supplied to the fuel system of the car.
Capacitive devices
These devices are the most popular, as they have a simple design, 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 the 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 in this way. The advantages of this type of structure 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 considered above. A pressure-sensitive conductive membrane is installed at a certain distance from the magnetic circuit in the form of the letter (an inductor is wound on 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 permeability at the gap is about 1000 times less than at the core, even its meager change leads to proportional fluctuations in the inductance values.
Optoelectronic sensors
They simply detect pressure, have a high resolution. They have high sensitivity and thermal stability. They work on the basis of light interference, and a Fabry-Perot interferometer is used to measure small displacements. Such electronic pressure sensors are extremely rare, but are quite promising.
The main components of the device:
- Crystal optical converter.
- Diaphragm.
- Light-emitting diode.
- Detector (consists of three photodiodes).
Fabi-Perot optical filters are attached to two photodiodes, which have a small difference in thickness. Filters are silicon mirrors with a reflective front surface. They are coated with a layer of silicon oxide, a thin layer of aluminum is applied to the surface. The optical converter is very similar to a capacitive pressure sensor.