A solenoid is defined as a coil of wire commonly in the form of a long cylinder that when carrying a current resembles a bar magnet so that a moveable core is drawn into the coil when a current flows. A more simple definition is that a solenoid is a coil and a moveable iron core used to convert electrical energy into mechanical energy. Solenoids have been around for decades but now range in size from less than one-quarter of an inch to more than 15 inches in diameter with force outputs of less than an ounce to a ton.
Rotary and linear solenoids operate in generally the same fashion. The direction of movement is either rotary or linear based on the mechanical assembly within which the electromagnetic circuit is encased.
Rotary solenoids provide rotational stroke measured in degrees. Some are unidirectional and some are bidirectional. Most have a spring return to bring the armature (moving member) back to the home position. Rotary solenoids are often used when package size is of the utmost importance and
the work they perform is distributed more evenly across their stroke. Rotary solenoids have higher starting force/torque than do linear solenoids. They are more resistant to shock. Rotary solenoids also offer far longer life (in number of actuations) than do linear solenoids. One of the most
common applications that helps to illustrate a rotary solenoid function is opening and closing a laser shutter.
Linear solenoids provide linear stroke usually less than one inch in either direction. Just like rotaries, some linear solenoids are unidirectional and some are bidirectional. Linear solenoids are usually classified as pull (the electromagnetic path pulls a plunger into the solenoid body) or a push type where the plunger / shaft is pushed out of the case. Many have a
spring return to bring the plunger or plunger and shaft back to the home position. Linear solenoids are less complex devices and are significantly less expensive than rotary products. They also offer fewer life cycles and sometimes tend to be larger. Linear solenoids are found in many varieties,
many sizes and configurations.