Proximity switch exhibiting improved start-up characteristics

A proximity circuit for sensing a target location comprising means for establishing an electro-magnetic sensing field having an amplitude, the presence of said target in said field changing said amplitude, a detecting circuit for detecting changes in said amplitude, a drive circuit operatively coupled to said means for establishing for providing a first energy level to maintain said sensing field, a start-up circuit operatively coupled to said drive circuit for providing a second energy level to said means for establishing to achieve a predetermined field amplitude rapidly after energization of the proximity circuit, and a timing circuit coupled to both the start-up circuit and the detecting circuit to activate the start-up circuit for a predetermined time and deactivate the detecting circuit for approximately the same predetermined time.

A proximity switch for indicating a target location comprising an induction coil, first drive means operatively coupled to said induction coil for maintaining an oscillating electro-magnetic field having an amplitude about said induction coil, the presence of said target in said field changing said amplitude, sensing means responsive to said electromagnetic field operatively coupled to said field for generating a signal indicative of when said target has come within a predetermined distance of said induction coil, second drive means operatively coupled to said first drive means for causing additional energy to pass to said induction coil after initiation of said field, and a timing circuit connected to the second drive means to maintain the additional energy level for a predetermined time while disabling the sensing means for approximately the same predetermined time.

A proximity circuit for indicating target location comprising a tank circuit, an oscillator drive circuit operatively coupled to said tank circuit for driving said tank circuit into oscillation having an amplitude, the amplitude level being a function of the distance between the target and the tank circuit, sensing means responsive to said oscillation amplitude for generating a signal indicative of a predetermined distance between said target and said tank circuit, a comparator circuit coupled to said sensing means for generating a signal indicative of said target coming within a predetermined distance of said tank circuit, and wherein said comparator circuit includes a hysteresis circuit for preventing said comparator circuit from switching from a target present signal to a target absent signal due to noise present on said signal from said sensing means, and start-up circuit means operatively coupled to said oscillator drive circuit for causing additional drive power to occur in said oscillator drive circuit when power to said oscillator drive circuit switches from a power-off to a power-on condition.

A proximity switch for detecting when a target is within a predetermined distance of a tank circuit, said proximity switch comprising a resonator drive circuit having a current drive source operatively coupled to a power supply and to said tank circuit and causing said tank circuit to resonate at an amplitude value, the presence of said target causing said amplitude to change, means responsive to changes in said amplitude value operatively coupled to said resonator drive circuit for generating a signal indicative of the target being within said predetermined distance of said tank circuit, start-up circuit means operatively coupled to said resonator drive circuit for causing additional current drive to occur in said resonator drive circuit when power to resonator drive circuit is switched from a power-off to a power-on condition and a timing circuit operatively coupled to said start-up circuit means, said timing circuit disabling said start-up circuit means after a predetermined amount of time has elapsed after power is applied to the proximity switch.

A proximity switch for detecting when a target is within a predetermined distance of a tank circuit, said proximity circuit comprising a resonator drive circuit having a PNP current mirror operatively coupled to said tank circuit, said tank circuit resonating when said target is beyond said predetermined distance, a start-up circuit having an NPN current mirror operatively coupled to said PNP current mirror, said NPN current mirror approximately doubling the gain of said PNP current mirror, enable means operatively coupled to said NPN current mirror for controlling when said NPN current mirror is enabled, detector circuit including a differential comparator operatively connected to said resonant circuit and a reference source, said detector circuit detecting and generating a signal indicating a target presence, and a comparator circuit operatively connected to a reference voltage and said detector circuit for comparing the signal indicative of target presence from said detector circuit against said reference voltage and generating a signal indicative of the target being within said predetermined distance.