Adapted line
We speak of an adapted (electrical) line if the electromagnetic wave propagating on the line is not reflected at its end. This is the case when the end is terminated with a terminating resistor identical to the line impedance ; in this case the reflection factor is equal to 0.
Optimal terminating resistor
The value of the terminating resistor is determined with sinusoidal signals with a standing wave measuring device or with pulse operation by time domain reflectometry . In this case, an impulse running along the line is completely absorbed by the terminating resistor.
In many data cables - especially in bus systems - such a terminating resistor is already integrated and can be switched on or off with a switch, for example with Profibus .
Incorrect adjustment
If the terminating resistor is chosen to be different from the line impedance, the signal is not completely absorbed by the terminating resistor and is partially reflected. In this case, with sinusoidal signals on the line, a standing wave is created which is the result of the superposition of the incoming and reflected, returning waves.
literature
- K. Küpfmüller and G. Kohn: Theoretical electrical engineering and electronics, an introduction . 16th edition. Springer, 2005, ISBN 3-540-20792-9 .