Pressure measuring sensor: description and device, principle of operation, classification

In modern industry of various directions, pressure measurement sensors are widely used. They serve for the most accurate measurement of readings in different environments and for further data acquisition in electrical or digital form. The main sensors are divided into optical, resistive, magnetic, piezoelectric, capacitive, mercury piezoresonance

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Sensor device

With this device, the parameters can change depending on changes in parameters in the measured medium, for example, liquid, gas, or steam. In the sensor, the characteristics of the measured medium are converted into a unified code for displaying the readings on the indicating device.

The sensor consists of a primary transducer, which includes a sensing element - a pressure receiver, secondary signal processing circuits, and various parts of the housing. In some cases, it is equipped with sealing parts for working conditions in humid and aggressive environments.

Classification of devices according to the principle of operation

From the principle of operation or the method used in converting an input signal to an electrical output, measurement sensors are classified:

• Strain gauge method. Sensitive parts measure resistance when acting on a strain gauge attached to an elastic element, which is deformed under pressure.
• Piezoresistive method. Works on the basis of integral sensitive silicon parts. Silicon converters are highly sensitive due to the ability to change the semiconductor resistance. To measure characteristics in non-aggressive environments, Low cost is used - a method of equipment execution when the sensitive element is not equipped with any degrees of protection. In the case of work in an environment where it is possible that an aggressive substance is exposed to the sensor, the sensitive element equipped with a sealed casing with a steel separating diaphragm, which transmits pressure by means of silicon liquid.
• Capacitive method. The main part of a sensor using this method is a capacitive cell. Its job is to change the electrical capacitance between the stacking of the capacitor and the measuring diaphragm, depending on. The main advantage is the protection against deformation; in the absence of pressure, the membrane regains its shape, while the calibration of such a sensor is not required. And also the high stability of the characteristics is due to the small influence of the temperature error due to the small volume of liquid that fills the inner volume of the cell.
• Resonant method. This principle is based on the change in the resonance frequency of an oscillating element during its deformation. Among the shortcomings, one can single out a long response time, and the impossibility of working in aggressive environments without loss of measuring accuracy.
• Inductive method. Based on the registration of vortex shackles. The measuring element consists of two insulated coils with a metal shield. The transmitter measures the displacement of the diaphragm when there is no actual contact between the two surfaces. Electric current is generated in the coils in such a way that the charge and discharge of the coil occurs at equal intervals of time. Changing the position of the diaphragm creates a current in the fixed coil, followed by a change in the inductance of the system. The bias of the data of the main coil makes it possible to convert the data into a standard signal, which in its parameters is proportional to the applied pressure.
• Ionization method. It works on the principle of registering the flow of ionized particles, like a lamp diode. The lamp is equipped with two electrodes, a cathode, an anode, and a heater in some cases. The advantage is the ability to record data in environments with low pressure, including vacuum, but such equipment cannot be operated at atmospheric pressure.
• Piezoelectric method. The idea is based on the piezoelectric effect, in which a piezoelectric element creates an electrical signal proportional to the effect of the medium being measured on it. Used to measure constantly changing acoustic and impulse media. Has a wide range of dynamic and private data measurement. It has a low weight, dimensions and high reliability in operation in difficult conditions.

Types of sensors

Capacitive. It has the simplest design, which includes two flat electrodes with a gap between them. One of them is made in the form of a membrane, which is influenced by the measured medium, as a result of which the gap between the electrodes changes. In essence, this type is similar to a variable gap capacitor. Such a sensor is able to register even a small change in readings.

Piezoelectric. The main structural element is a piezoelectric element, a material that outputs a signal when measured characteristics are applied to it. It is located in the measured medium, and emits a current depending on the magnitude of the pressure change. But due to the fact that this element changes its output only when the environment changes, then with constant parameters, it will not show any data, and is suitable for work only in an environment where pressure is intermittent changes.

Optic.

The device of operation of such sensors can be based on two principles of operation:

• Fiber optic. It is the most accurate and the measurement work does not depend on changes in temperature conditions. The main part for measurement is an optical waveguide. A conclusion is made about the magnitude of the pressure measurement in such devices by the change in the amplitude and polarity of the transmitted light through the sensitive part.
• Optoelectronic. It consists of a multi-layer transparent structure through which light passes. Moreover, one of these layers can change the refractive index and layer thickness depending on the applied pressure.

The illustration below shows schematically both methods of operation. Figure, A - change in refraction, figure B - change in layer thickness.

Mercury.

An elementary and technically simple sensor. It works on the basis of two communicating vessels, one of which is pressurized, and the second is analogously outputted data, and is determined by a parallel-aligned measuring scale.

Magnetic.

Works on the basis of the inductive method. The sensitive part consists in an E-shaped bar, in the middle of which there is a coil, and a sensitive membrane, through which the measured parameters are transmitted. The membrane is located near the plate, at a short distance from the edge. The coil, when turned on, creates a magnetic flux, which in turn follows through the bar, gap and membrane. The permeability of the magnetic gap is several hundred times less than the permeability of the strip and membrane, therefore, the inductance changes even with a slight change in the gap size.

Piezoresonance.

It works on the basis of the piezoelectric effect, but with one difference - in this case, the inverse effect of the piezoelectric element is used, based on the change in the shape of the material depending on the incoming current. This sensor uses a resonator on which two electrodes are located on opposite sides, on them alternately current of different polarity is supplied, and as a result of this, the plate is bent in different directions, taking into account the supplied frequency.

Difference from a pressure gauge

The main difference between this kind of sensor and a manometer is that it is a device designed to measure characteristics without converting it. In a manometer, the readings of the device depend on the measured characteristics, which are displayed on its analog device or display.