Simply put, an impulse relay stores a pulse of electrical energy until that energy is later released. An electrical relay is generally a type of switch/coil assembly that is activated when an electric current is introduced. The main difference between an impulse relay and a common relay is that a common relay requires a constant application of electricity, while an impulse relay does not. An impulse relay only requires a brief connection to the electric current, and it can then relay that energy at a later time. When the switch is turned off, and the electric current is disconnected, the relay preserves, or remembers, its last state.
There are two common ways in which an impulse relay can be constructed. The first method is by using a solenoid operating a ratchet and cam mechanism. A solenoid is a type of cylindrical current-carrying coil that will act as a magnet when introduced to an electric current. This type of impulse ray construction is sometimes referred to as the one coil method. If the impulse ray is constructed using this method, the initial introduction of electricity activates the relay, or turns the relay on, and the second pulse of electricity to the coil then turns the relay to the off position.
The alternative method for constructing an impulse relay is by using two opposing coils connected by a magnetic device that holds the contact ends in position while the coils are charged with the current, and while they are at rest. When this type of impulse relay is used, the first electric pulse of energy connects with the first coil and turns the relay on, while the second pulse of energy to the alternative coil terminates the impulse relay, or turns it to the off position.