Metal detector and checking arrangement therefor

Claim 2

In circuitry arrangement always sensitive for detecting metal objects in uninterruptedly flowing nonmetallic material and for continually checking the operation of the arrangement; an emitter coil and means for energizing the emitter coil to establish a field, a receiver coil linked by the field of said emitter coil, said emitter and receiver coils being so positioned relative to the flowing material that the said field will be changed by metal objects in said material, a checking coil operable when energized to change the field linking said receiver coil, pulse generating means for periodically generating checking pulses and operatively connected to said checking coil to cause the periodic energization thereof, first means connected to said receiver coil and operable to develop signals in response to changes in the field linking said receiver coil, the duration of the change in the field linking said receiver coil due to a metal object in said material being substantially greater than the duration of the said change due to the periodic energization of said checking coil, first signalling means connected to said first means and operable to develop a signal in response to a signal from said first means of a duration greater than that caused by a said periodic energization of said checking coil, electronic switching means connected between said first means and said first signalling means that serve to hinder passing along of periodically appearing checking pulses though permitting passage of impulse signals of a duration greater than that of the checking pulses, and second signalling means connected to said pulse generating means and to said first means and operable to develop a signal in response to the absence of a signal from said first means in response to the energization of said checking coil.

Claim 3

In circuitry arrangement always sensitive for detecting metal objects in uninterruptedly flowing nonmetallic material and for continually checking the operation of the arrangement; an emitter coil and means for energizing the emitter coil to establish a field, a receiver coil linked by the field of said emitter coil, said emitter and receiver coils being so positioned relative to the flowing material that the said field will be changed by metal objects in said material, a checking coil operable when energized to change the field linking said receiver coil, pulse generating means for periodically generating checking pulses and operatively connected to said checking coil to cause the periodic energization thereof, first means connected to said receiver coil and operable to develop signals in response to changes in the field linking said receiver coil, the duration of the change in the field linking said receiver coil due to a metal object in said material being substantially greater than the duration of the said change due to the periodic energization of said checking coil, first signalling means connected to said first means and operable to develop a signal in response to a signal from said first means of a duration greater than that caused by a said periodic energization of said checking coil, and second signalling means connected to said pulse generating means and to said first means and operable to develop a signal in response to the absence of a signal from said first means in response to the energization of said checking coil, a first bistable circuit having an output and having an input connected to each of said first means and said pulse generating means and an And gate having an input connected to the output of said first bistable circuit and an input connected to said pulse generating means and having an output, a second bistable circuit having an output connected to said second signalling means and having an input connected to said first means and an input connected to the output of said And gate.

Claim 4

In circuitry arrangement always sensitive for detecting metal objects in uninterruptedly flowing nonmetallic material and for continually checking the operation of the arrangement; an emitter coil and means for energizing the emitter coil to establish a field, a receiver coil linked by the field of said emitter coil, said emitter and receiver coils being so positioned relative to the flowing material that the said field will be changed by metal objects in said material, a checking coil operable when energized to change the field linking said receiver coil, pulse generating means for periodically generating checking pulses and operatively connected to said checking coil to cause the periodic energization thereof, first means connected to said receiver coil and operable to develop signals in response to changes in the field linking said receiver coil, the duration of the change in the field linking said receiver coil due to a metal object in said material being substantially greater than the duration of the said change due to the periodic energization of said checking coil, first signalling means connected to said first means and operable to develop a signal in response to a signal from said first means of a duration greater than that caused by a said periodic energization of said checking coil, and second signalling means connected to said pulse generating means and to said first means and operable to develop a signal in response to the absence of a signal from said first means in response to the energization of said checking coil, a first bistable circuit having an output and having an input connected to each of said first means and said pulse generating means and an And gate having an input connected to the output of said first bistable circuit and an input connected to said pulse generating means and having an output, a second bistable circuit having an output connected to said second signalling means and having an input connected to said first means and an input connected to the output of said And gate.

Claim 5

An arrangement according to claim 2 which includes delay means interposed between said first means and said first signalling means and having a delay period greater than the duration of a period of energization of said checking coil.

Claim 6

An arrangement according to claim 2 in which the interval between successive pulses from said pulse generating means is greater than the length of time that a metal object in said material will influence the field linking said receiver coil.

Claim 7

An arrangement according to claim 3 in which said delay means comprises a component which develops a sawtooth output with each rise having a duration substantially greater than the duration of the change in the field linking said receiver coil due to energization of said checking coil.

Claim 8

An arrangement according to claim 5 in which said first signalling means has a threshold which is reached by the output of said delay means only upon a said rise of greater duration than that of a rise developed in response to energization of said checking coil.

Claim 9

An arrangement according to claim 4 in which the pulses from said pulse generating means occurs at about 300 millisecond intervals whereby the checking of said arrangement is substantially continuous.