In many applications, the current transmitter is used to convert the signal that the single chip microcomputer cannot directly measure into the electrical analog signal that the single chip microcomputer can process, such as the current transmitter, pressure transmitter, temperature transmitter, flow transmitter and so on. Most of the early transmitters are voltage output type, that is, the measurement signal is converted to 0-5V voltage output, which is the direct output of the op amp, the signal power is <0.05W, and the digital signal is converted by the analog/digital conversion circuit for the single-chip microcomputer to read and control.

A remote instrument in which the water in the lower part of the instrument and the condensed water in the upper part of the steam are sent through the instrument tube to both sides of the bellows of the transmitter, and the differential pressure on both sides of the bellows drives the mechanical amplifying device to indicate the water level with a pointer. Of course, the electrical analog quantity is changed into a digital quantity can also be called a transmitter. The above is just a conceptual illustration of the difference between sensors and transmitters. The two-wire current output current transmitter has been widely used because of its high anti-interference ability.