Solenoid motion detection circuit

Details Solenoid motion detection circuit Solenoid motion detection circuit

1999-04-13

2001-04-03

Patidar, Jay (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207240

Reexamination Certificate

active

06211665

ABSTRACT:

TECHNICAL FIELD
This invention pertains to monitoring and control apparatus, in general, and to a method and apparatus for indicating movement of a moveable member of an electromagnetic device, in particular.
BACKGROUND OF THE INVENTION
Electromagnetic devices such as solenoid devices are in widespread use. In certain applications, there is a need to perform test and fault detection on solenoid operators. In many of these applications, the solenoid device is disposed at a remote location or is otherwise inaccessible. Prior art has attempted to solve this challenge but has been limited to voltage-drive applications (U.S. Pat. No. 4,321,946 “Armature Position Monitoring and Control Device” and U.S. Pat. No. 4,907,901 “Method and Apparatus for Measuring Displacement of a moveable Member of an Electromagnetic Device by Using Perturbations in the Device's Energizing Current”) or has required separate and added sensors (U.S. Pat. No. 3,789,876 “Solenoid Valve with Electronic Position Indicator” and U.S. Pat. No. 4,692,678 “Closed Loop Servo Control System”).
High response solenoids using current drive controllers require more sophisticated circuitry, in order to capture armature motion, that is not provided in the prior art. The invention herein described solves these problems.
SUMMARY OF THE INVENTION
In accordance with the invention, a circuit for detecting motion of an electromagnetic device is provided. The electromagnetic device includes coil and a movable member. The circuit detects coincidence of energization of the device coil and reverse rates of change of the coil current and voltage waveforms. These are indicated by monitoring the first differentials of the coil current and voltage versus time waveforms. The differentiated signals are compared to thresholds in order to screen out circuit noise. The circuit also includes delay and one-shot timer networks to create valid timing windows. The comparator and valid window signals are then ANDed to produce event signals from the current and voltage paths. These two event signals are then ORed together and routed through a flip-flop device. When either a current or voltage event occurs, the flip-flop output is toggled. The flip-flop is reset each time power is applied to the solenoid.
When the armature moves, either the current path or the voltage path will signal the motion detected event. If motion occurs before current limit is achieved, the current path detects the event. If motion occurs after current limit is achieved, then the voltage path detects the event. The current and voltage waveforms are subjected to reverse slopes because of the back-EMF (electro-motive-force) generated by the armature moving within the magnet field of the solenoid.


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