Final answer:
Latching relays or impulse relays have contacts that prevent continuous power from being applied to the coil after it has been energized. They use a mechanical or magnetic mechanism to maintain the contact position without constant power and are used in control circuits and power-switching applications.
Step-by-step explanation:
The devices that have contacts designed to prevent continuous power from being applied to the coil after it has been energized are known as latching relays or impulse relays. When the coil of a latching relay is energized, it changes its state and remains in that state until it receives another impulse. This functionality is particularly useful in applications where it is important to maintain the state of the relay even in the absence of power.
Latching relays are composed of two main parts: the coil and the contacts. Unlike standard relays, which require continuous power to maintain their state, latching relays employ a mechanical or magnetic mechanism that keeps the contacts in an open or closed position after the coil has been de-energized. This feature is beneficial in power-saving applications, or situations where the power supply is unreliable or needs to be minimized.
To 'set' the relay, a current is passed through the coil, which then moves the contacts into the desired position. Subsequently, when the coil is de-energized, the contacts remain in their last position due to a mechanical latch or residual magnetism in the relay's core. To 'reset' the relay, a separate current pulse is sent in the opposite polarity or to a separate reset coil, which releases the latch or demagnetizes the core, thus returning the contacts to their original state.
Relay logic is an area in electrical engineering where latching relays are widely applied, and they are often used in control circuits and power switching applications. Their ability to maintain an on or off state without continuous power makes them ideal for various industrial and automation settings.