Telegraph Relay

a sensitive electromechanical device used to amplify, separate, and convert DC and AC telegraph signals. Telegraph relays have high operating speeds, and they can be controlled by low current. They are usually polarized; that is, they operate during a change in direction of the control current and not during a change in the absolute value of the current. Since the 1960’s, electromechanical telegraph relays have been gradually replaced by electronic devices.