What are Transmission lines?

They are used to carry the measurement signal from the measuring device to the controller. In the past the

transmission lines were pneumatic (compressed air or compressed liquids) but with the advent of

the electronic analog controllers and especially the expanding usage of digital computers for control, the

transmission lines carry electric signals.

Many times the measurement signal coming out from a measuring device is very weak, and it cannot be

transmitted over a long distance. In such cases the transmission lines are equipped with amplifiers which

raise the level of the signal. For example, the output of a thermocouple is of the order of a few mil 3. iv0I.t

s . Before it is transmitted to the controller, it is amplified to the level of a few volts.