The sensor is able to convert a physical quantity corresponding to the measured electrical signal.

Usually the sensitive portion of the sensor and the signal converting part, wherein the sensitive portion of the output signal to direct experience of the measured physical quantity, produces a certain function of the measured physical child relationship; sensitive output signal converting portion will be converted into the corresponding portion of the electrical signal. Such as pressure sensors, acceleration sensors, in general by the sensitive portion and the signal converting section two parts.

Some sensitive directly measured physical quantity sensor outputs an electrical signal with a certain function relationships. Such as temperature, humidity sensor, the temperature is output directly into an electrical signal or a function of the humidity of.

Sensor signals are output forms, generally resistors, capacitors, voltage, current, frequency, pulse, etc..

Many types of sensors, classification lot. For example, the characteristics of the output signal according to the classification can be divided into analog and digital sensor signal the sensor signal. Be classified according to physical phenomena can be divided into the structure and physical properties of sensor type sensor. As is the use of pressure sensors shrapnel shrapnel structural parameters to change the measured pressure, of a structural type sensor; temperature sensitive resistor and the resistance of the physical characteristics of use to the side with the temperature change amount of the temperature sensor is a physical characteristic.

The sensor is two classifications: the first level is classified as a displacement sensor according to the measured physical pressure sensor , temperature sensor , etc.; the second stage is classified as a resistive sensor according to the principle of the sensor measurement and the conversion capacitance sensors, inductive sensors.

Sensor uses two categories for the purpose, because the design of the automatic control system, you first need to choose based on the alleged physical sensors. When selecting a specific sensor and need to performance, environmental requirements, and with the price and the control circuit elements such factors into account the principle of measurement and the conversion of the sensor.

If an automatic control system compared to a person, the control circuit is the human brain and nerves, the actuator is a man's hand, and the sensor is human sensory organs. Thus the role of automatic control systems, sensors.

When using a sensor, depending on the circuit connections in general, the choice of the voltage, current, frequency or pulse signal as the output of the sensor.

Generally, in addition to providing the necessary power to the sensor, but also the output signal of the sensor is converted into a signal of the automatic control system needs. In addition, the output signal of the sensor is generally relatively small, it still needs to be enlarged. Thus, the sensor circuit is generally connected to a preamplifier, the signal conversion circuit to complete the work and signal amplification. For example, an automatic temperature control system, temperature sensing resistor to measure the temperature, the general temperature sensing resistor connected to a preamplifier circuit that converts the measured temperature changes with the resistance value into a voltage value, as an automatic control system The input signal, and the signal is amplified pickup person, then the signal is processed by the control circuit, and the control and drive the implementation of part of the temperature control.

The role of automatic control system is controlled automatic control and regulation of one or more physical objects. To achieve the goal of the control system, it is necessary to accurately measure these quantities need to be controlled as a precondition. Therefore, the sensor is an important part of the automatic control system, is an automatic control system to meet the demand, and select the appropriate sensor has a direct relationship. In the selection of sensors, you first need to consider is the performance of the sensor, it must not be less than the index of the automatic control system requirements, and I have a certain child, the choice of indicator systems than an order of magnitude of the sensor under normal circumstances. E.g., the aforementioned temperature control system, if its temperature is the temperature control precision error of less than 1 ℃, measurement accuracy is typically chosen to be about 0.1 ℃ temperature sensing resistors to measure temperature.

Moreover, in the selection of sensors, according to the automatic control system to cope with the situation and environment select the type of sensor. For example, in the form of a variety of power sensors to choose from, should be selected in a manner consistent with the automatic power control system sensors. Another example. For steelmaking blast temperature control system, it must be able to adopt the amount of high-temperature side of the sensor.

In addition, the higher the performance of the sensor, the more expensive price. In the selection of sensors, should be considered the performance of the control system, the choice of the best price-performance sensors. To avoid the phenomenon of blind pursuit of high-performance sensors, because in the limited performance itself or actuator control system, using high-performance sensor is purely a waste.