Although latching solenoids have been available for many years, they are receiving a new wave of interest that is being driven by the current focus on energy efficiency, due in part to cost savings, environmental concerns, and power availability; the adaptability of these solenoids to a wide variety of applications; and lastly, technology has now advanced enough to allow for fail-safe functionality in the small package size that design teams often require. Integrating fail-safe functionality to latching solenoids will be the focus of this tech brief.
First, it is important to review how latching solenoids work and why they are so energy efficient. Latching solenoids draw very little power because they do not require constant power to maintain a commanded state. This makes latching solenoids ideal for applications with a low cycle rate. Only a short pulse of power is needed to move the armature into either the latched or de-latched position. A pulse of power of one polarity is used to move the armature into the latched position. The armature is then held in position either by a permanent magnet or residual magnetism (depending on the solenoid’s design). A pulse of power of the opposite polarity cancels the magnetic hold, and the armature is driven back to its base position by a spring, although other means can be used as required by the application.