Sensors are devices that receive signals or stimulate and react, and can convert physical or chemical quantities to be measured into another corresponding output device. Used for automatic control, security equipment and so on. In stimulus theory, in order to obtain electrical stimulation, electronic stimulation devices are often used during this period of time.

And one of the devices that has been used for a long time is an induction coil, but it's not used much anymore, and it's mostly replaced by vacuum tubes and semiconductor stimulation devices.

The effect of a sensor's input on its output is called the sensing coefficient. A mercury thermometer, for example, when the temperature rise of 1 ° C, the mercury rises 1 cm, is the mercury thermometer sensing coefficient of 1 cm / ° C.

A sensor is an ideal sensor when its input and output are completely linear. At the same time, the ideal sensor should also follow the following principles:

1. Only affected by the factors under test;

2. Not affected by other factors;

3. The sensor itself will not affect the factors under test.