Nonlatching

Nonlatching is a term used in engineering to describe devices or circuits that do not retain their actuated state after the input signal is removed. A nonlatching device returns to a defined rest state automatically when actuation ends. This is the opposite of latching or bistable devices, which continue to hold their state without continuous input.

In relays and switches: Nonlatching relays, also called monostable relays, require continuous energization to stay in the actuated position. When the drive current is removed, the contacts return to their default position, often via an internal spring. They are typically implemented with normally open or normally closed contacts. Nonlatching relays are simple and inexpensive, but their actuation energy is consumed as long as the state is maintained.

Other uses: In sensors, alarms, and logic circuits, nonlatching can describe outputs or indicators that reset automatically when the triggering condition ceases, rather than staying set until cleared. In contrast, latched outputs retain their state until an explicit reset or opposite action occurs.

Tradeoffs and design considerations: Nonlatching devices offer straightforward behavior and faster release, but require continuous input to maintain actuation and may be more susceptible to noise-induced switching. They are chosen when a safe default state and low risk of stuck conditions is needed, or when power can be readily supplied. Latching devices are used when it is desirable to hold a state with minimal power, or to endure brief power loss without losing state.