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(in Russian, datchik; also pickup), an element of a measuring, signaling, regulating, or control device in a system that converts the value being monitored (such as pressure, temperature, frequency, velocity, displacement, voltage, or electric current) into a signal that is convenient for measurement, transmission, conversion, storage, and recording, as well as for influencing the processes being regulated.
A sensor usually contains a receiving (sensing) member, as well as one or more intermediate converters (see Figure 1). However, the sensor frequently consists only of the receiving member (for example, a thermocouple, a resistance thermometer, or a strain gauge). The output signals of a sensor are distinguished according to the type of energy (electrical, mechanical, pneumatic, or less frequently, hydraulic) and the type of modulation of the energy flow (amplitude, frequency, phase, or discrete [coded]).
The operation of the most common sensors is based on a
change in the electrical resistance, capacitance, inductance, or mutual inductance of an electrical circuit (resistance transducers, capitance sensors, and inductance sensors). Another widely used type of sensor generates an electromotive force as a result of influences by the mechanical, acoustic, thermal, electrical, magnetic, optical, or radiation quantity being measured or monitored. This category includes strain gauges, piezoelectric pickups, and photocells.
The operation of sensors is characterized by the law governing the change in the value of the output (y) as a function of a change in the value of the input (x), the limits of the change in the input values (xmln - xmax) and the output values (ymin - ymax), sensitivity S = Δy/Δx, the sensitivity threshold (the value of the minimum effect to which a sensor will respond), and time parameters (time constants).
According to the classification established by the State System of Automation Devices and Components (GSP), sensors are classified as technical means of data collection and primary processing of measurement and monitoring information. Sensors are one of the basic elements in remote-control measuring devices, in telemetry and telesignalization, in regulation and control applications, and in various devices and equipment used in physics, biology, and medicine for monitoring the vital processes of humans, animals, and plants (biological sensors). Sensors are of great importance in the automation of production processes, where they are used to measure and record the density and concentration of solutions, the composition and properties of substances, the dynamic viscosity and fluidity of various mediums, humidity, transparency, color intensity, layer thickness, temperature, elasticity, the concentration of charge carriers, and other parameters characterizing a technical process. Sensors used for such purposes often utilize ultrasonic, radio-frequency, optical, and radiation measuring methods. Random-number pickups are used to simulate real conditions in testing automatic control systems and in computer technology for solving problems by statistical methods.
Specific requirements are made of the output signals and characteristics of sensors used in machines for centralized monitoring and control. The successive connection of large numbers of sensors to the same measuring device requires a high degree of uniformity of the sensors’ output parameters. In some cases the term “sensor” is used to designate the entire transmitting portion of a remote-control mechanical device or automatic device.
REFERENCESAgeikin, D. I., E. N. Kostina, and N. N. Kuznetsova. Datchiki kontrolia i regulirovaniia, 2nd ed. Moscow, 1965.
Turichin, A. M. Elektricheskie izmereniia neelektricheskikh velichin, 4th ed. Moscow-Leningrad, 1966.
Elektricheskie izmeritel’nye preobrazovateli. Edited by R. R. Khar-chenko. Moscow-Leningrad. 1967.
Dolgov, V. A., and A. V. Kelin. Elektronnye datchiki dlia av-tomaticheskikh sistem kontrolia. Moscow, 1968.
M. M. GEL’MAN
sensor, detector, sensing device
Analog sensors most often produce a voltage proportional to the measured quantity. The signal must be converted to digital form with a ADC before the CPU can process it.
Digital sensors most often use serial communication such as EIA-232 to return information directly to the controller or computer through a serial port.