Sensor introduction and selection guide

1: Introduction to the sensor

　In the broadest sense, a sensor is a device or device that can convert a certain physical or chemical quantity into an electrical signal that is easy to capture and use. The relevant definition of the International Electrotechnical Commission is: "The sensor is a pre-component in the measurement system, which converts the input variable into a signal that can be measured." According to Gepu et al., "a sensor is a sensitive element that includes a carrier and a circuit connection", and "a sensor system is a sensor that combines a certain information processing (analog or digital) capability." The sensor is an integral part of the sensor system, it is the first pass of the measured signal input.

　If computers and programmable controllers are likened to the "brains" of automated control systems, then sensors are the "eyes" of automated control systems, and are the information feedback devices and originals of mechatronics. The control system composed of computer processing unit, actuator, and internal feedback of the actuator is called an open-loop control system; a control system composed of computer processing unit, actuator, internal feedback of the actuator, and external sensor information feedback of the execution effect, Closed loopcontrol.

The electrical signal of the sensor has analog quantity type and digital quantity type: the analog quantity is to simulate the size of the measured physical quantity with the output of current or voltage. If the analog quantity signal output by the sensor is already an international standard signal, for example, 4-20mA , 0-20mA, 1-5V, 0-10V, etc. Such sensors are sometimes called transmitters.

The electrical signal of the sensor sometimes uses voltage and current higher than a certain domain setting or lower than a certain domain setting to represent the digital information of 1 or 0, or use the light signal to transmit information, such a sensor is a digital quantity Output type.

　2: Sensor series classification

　According to the original internal measurement:

Resistance strain sensor

　Capacitive sensor

　Inductive sensor

　Piezoelectric sensor

　Magnetoelectric sensor

　Pyroelectric sensor

　Photoelectric sensor

　Optical fiber sensor

　According to the measured physical or chemical quantity:

Pressure Sensor

Motion detector

Flow Sensors

　Angular displacement sensor

speed sensor

Temperature Sensor

Humidity Sensor

　Wind speed sensor

　 Tension sensor

　Gas detection sensor

　Microwave Sensor

biological sensor

　……..

　3: Key points for sensor selection

　1) Input range (this is the most basic point of all selected sensors, such as displacement: 0-100mm; pressure 0-200 bar...)

　2) Output signal (this depends on the received signal of the controller corresponding to the selected sensor, the standard analog signal has 4-20Ma, 0-10V, digital

RS422...)

　3) Accuracy requirements (Accuracy parameters include resolution, non-linearity, maximum deviation, etc., we must base on the best accuracy required by our site as the standard,

Not that the higher the accuracy, the better, the actual requirements shall prevail)

4) Power supply voltage (Because the standard sensor is connected to the PLC, the voltage used under normal circumstances is DC 24V, but there are also special ones, such as 5VDC, or others, this must be understood in advance)

5) Mechanical interface connection part (the sensor is the best example of mechatronics, so the mechanical part is also very important. Before choosing a sensor, the mechanical specifications of the sensor must be determined, such as thread Interface: G 1/4, 1/4 NPT, M23X12, etc., if the specifications are not correct, the purchase will be very troublesome)