In many applications controlled by single-chip microcomputers, transmitters are used to convert signals that cannot be directly measured by single-chip microcomputers into electrical analog signals that can be processed by single-chip microcomputers, such as current transmitters, pressure transmitters, temperature transmitters, flow transmitters, etc.

Most of the early transmitters were voltage output type, that is, the measurement signal was converted into 0-5V voltage output, the signal power was <0.05W, and the digital signal was converted through the analog/digital conversion circuit for the single-chip microcomputer to read and control. However, in situations where the signal needs to be transmitted over long distances or the power grid interference in the use environment is large, the use of voltage output sensors is greatly limited, exposing the shortcomings of poor anti-interference ability, line loss destroying accuracy, etc., and two-wire current output transmitters have been widely used with their extremely high anti-interference ability.

The voltage output type transmitter has very poor anti-interference ability, and the line loss damages it, so it can't be said that the accuracy is high. Sometimes the output DC voltage is superimposed with AC components, which makes the single-chip computer misjudge and control errors occur. In serious cases, it will damage the equipment. The output 0-5V must not be transmitted remotely, because the line voltage drop is large after remote transmission, and the accuracy is greatly reduced. Now many ADC, PLC, and DCS input signal ports are made into two-wire current output type transmitters 4-20mA, which proves the inevitable trend of voltage output type transmitters being eliminated.