A Terminating resistor is an electrical resistor that is connected at the end of a transmission line (e.g. coaxial cable, twisted pair cable or field bus) to prevent signal reflections. These reflections occur when a wave (signal) hits a line termination that does not correspond to the characteristic impedance of the line. Such reflections can lead to signal distortion, data errors or malfunctions.
The incident wave is completely absorbed by a correctly dimensioned terminating resistor - the value of which corresponds to the characteristic impedance or line resistance. In this case, the reflection factor (ratio of the amplitude of the reflected wave to the amplitude of the incident wave) is zero, so that the signal is transmitted without distortion.
Terminating resistors are typically used at both ends of a transmission path, especially for fast digital signals, bus systems or sensitive measurement signals. Incorrect or missing termination can result in significant communication faults.