Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field of the Invention
This invention relates to a circuit for detecting the movement of a solenoid armature associated, for example, with a solenoid valve, whereby correct or incorrect operation of the armature, and therefore of the valve, may be monitored, especially from a remote location.
2. Description of the Related Art
Pneumatically operated systems, for example, typically comprise a large number of solenoid valves which function in a predetermined, desired sequence and control the operation of pneumatic devices such as cylinders. Usually, operation of the system is monitored from a remote, central console and it would be desirable to provide, as part of the console, means to indicate that each solenoid armature is operating correctly, or not, as the case may be. It is an object of the present invention to provide such means, and this object is achieved by relying on the observation that, when a solenoid armature moves in response to energisation of the solenoid coil, the inductance of the coil changes which causes the current flowing through the coil to drop momentarily.