Latching solenoids have been available for many years, and they are receiving renewed attention because of their reputation for being energy efficient and their adaptability to a wide variety of applications. Latching solenoids do not need constant power to maintain a commanded state. As a result, they use very little power and generate very little heat. The most common type of latching solenoid provides only two armature positions: fully extended or fully retracted. But some applications require a solenoid with three positions.
Before discussing the design and function of the three-position latching solenoid, it is important to review the basics of latching solenoid technology. Latching solenoids are ideal for applications with a low cycle rate because 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.