Electronic warning and monitoring apparatus and electrode arrangement therefor

A moving machinery safety means comprising:

• a central monitoring circuit for delivering a warning or control signal upon receipt of an activating signal;
• a device for detecting changes of an electromagnetic field including in combination a central constant frequency generator, at least two sensor circuits energizing by said central frequency generator, each sensor circuit including as L/C-circuit having at least one sensor-electrode creating an electromagnetic field and comprising a resonance-frequency defining element of the said L/C-circuit for changing the resonance-frequency if the sensor-electrode approaches to or comes in contact with an object, each sensor circuit further including a trigger circuit connected to the output of said L/C-circuit, which trigger circuit includes means for varying the current consumption of the sensor circuit for triggering a change in the said current consumption upon a certain change in the L/C-circuit frequency;
• a central current supply means which is connected to and supplies the sensor circuits through a common supply line;
• a current monitoring circuit also connected to the central current supply means for delivering an activating signal to the central monitoring circuit when the current consumption rises above or falls below a respective reference value;
• and an oscillator monitoring circuit for functional monitoring of the constant frequency generator and for delivering a warning signal if the frequency generator malfunctions.