A sensor is a generic term for a device or device that can be measured and converted into a usable output signal according to a certain rule, usually consisting of a sensitive component and a conversion component. When the output of the sensor is a specified standard signal, it is called a transmitter.

The concept of a transmitter is an instrument that converts a non-standard electrical signal into a standard electrical signal. A sensor is a device that converts a physical signal into an electrical signal. In the past, physical signals were often used, and other signals are now available. The primary instrument refers to the on-site measuring instrument or the base control table. The secondary instrument refers to the instrument that uses the primary signal to complete other functions: functions such as control and display.

Sensors and transmitters are the concept of thermal instrumentation. The sensor converts non-electrical physical quantities such as temperature, pressure, liquid level, material, gas characteristics, etc. into electrical signals or sends physical quantities such as pressure, liquid level, etc. directly to the transmitter. The transmitter amplifies the weak electrical signal collected by the sensor to transfer or activate the control element. Or a signal source that converts the non-electricity of the sensor input into an electrical signal while amplifying it for remote measurement and control. The analog quantity can also be converted to a digital quantity as needed.

The sensor and transmitter together form an automatically controlled monitoring signal source. Different physical quantities require different sensors and corresponding transmitters. There is also a transmitter that does not convert physical quantities into electrical signals, such as a "differential pressure transmitter" for a boiler water level gauge. It sends the lower water in the level sensor and the condensate from the upper steam through the meter tube. On both sides of the bellows of the transmitter, a differential meter on both sides of the bellows drives a remote meter that the mechanical amplifying device uses a pointer to indicate the water level. Of course, it is also possible to convert the electrical analog quantity into a digital quantity.