Ultrasonic intrusion detection system signal processing circuit

Claim 2

An ultrasonic motion detector device which receives an ultrasonic acoustic wave radiated into a space to be protected at an essentially constant carrier frequency and amplitude and which produces an alarm signal when the modulations of a received wave are characteristic of an alarm condition, comprising: A. means for producing an electrical signal which is representative of the amplitude modulations of a received ultrasonic wave; B. means for producing an alternating signal in response to said electrical signal, said alternating signal having a frequency corresponding to the frequency of said electrical signal but the difference between the high and low amplitudes of an excursion of said alternating signal being a first value when the absolute value of the electrical signal amplitude is greater than a predetermined reference amplitude and being another value less than the first value when the absolute value of the electrical signal amplitude is less than the predetermined reference amplitude; C. means for passing said alternating signal as an output signal when the frequency of said alternating signal is within a predetermined passband; D. means for producing an alarm signal in response to an output signal which corresponds to a train of a predetermined number of alternating signal excursions of said first value occurring within a predetermined time.

Claim 3

An ultrasonic motion detector device according to claim 1 further comprising means for effectively varying said predetermined reference amplitude in direct proportion to the time average of the output signal amplitude.

Claim 4

An ultrasonic motion detector device which receives an ultrasonic acoustic wave radiated into a space to be protected at an essentially constant carrier frequency and amplitude and which produces an alarm signal when the modulations of a received wave are characteristic of an alarm condition, comprising: A. means for producing an electrical signal which is representative of the amplitude modulations of a received ultrasonic wave; B. a saturation amplifier for producing an alternating signal in response to said electrical signal, said alternating signal having a frequency corresponding to the frequency of said electrical signal but the difference between the high and low amplitudes of an excursion of said alternating signal being a first value when the absolute value of the electrical signal amplitude is greater than a predetermined reference amplitude and being another value less than the first value when the absolute value of the electrical signal amplitude is less than the predetermined reference amplitude; C. an active filter for passing the alternating signal as an output signal having a pass-band of from about 50 Hz. to 200 Hz.; and D. means for producing an alarm signal in response to an output signal which corresponds to a train of a predetermined number of alternating signal excursions of said first value occurring within a predetermined time, which means comprises an integrator having a charge time constant and a discharge time constant greater than said charge time constant, which integrator is responsive to one-half of each output signal corresponding to one-half of an alternating signal excursion to store a charge at a rate determined by said charge time constant and responsive to the other one-half of each output signal to reduce the stored charge at a rate determined by said discharge time constant and an amplitude detector responsive to the stored charge reaching a predetermined level to produce an alarm signal

Claim 5

An ultrasonic motion detector device which receives an ultrasonic acoustic wave radiated into a space to be protected at an essentially constant carrier frequency and amplitude and which produces an alarm signal when the modulations of a received wave are characteristic of an alarm condition, comprising: A. means for producing an electrical signal which is representative of the amplitude modulations of a received ultrasonic wave; B. a saturation amplifier for producing an alternating signal in response to said electrical signal, said alternating signal having a frequency corresponding to the frequency of said electrical signal but the difference between the high and low amplitudes of an excursion of said alternating signal being a first value when the absolute value of the electrical signal amplitude is greater than a predetermined reference amplitude and being another value less than the first value when the absolute value of the electrical signal amplitude is less than the predetermined reference amplitude; C. an active filter for passing the alternating signal as an output signal having a pass-band of from about 50 Hz. to 200 Hz.; and D. means for producing an alarm signal in response to an output signal which corresponds to a train of a predetermined number of alternating signal excursions of said first value occurring within a predetermined time, which means comprises an integrator having a charge time constant and a discharge time constant greater than said charge time constant, which integrator is responsive to one-half of each output signal corresponding to one-half of an alternating signal excursion to store a charge at a rate determined by said charge time constant and responsive to the other one-half of each output signal to reduce the stored charge at a rate determined by said discharge time constant and an amplitude detector responsive to the stored charge reaching a predetermined level to produce an alarm signal

Claim 6

An ultrasonic motion detector according to claim 3, wherein the saturation amplifier comprises a first common emitter amplifier which receives the electrical signal as its input, a second common emitter amplifier coupled in series with the first common emitter amplifier, and wherein the means for effectively varying the predetermined amplitude comprises a feedback network for time-averaging the charge stored in said integrator and for loading the output of said first common emitter in direct proportion to said time-averaged charge.

Claim 7

An ultrasonic motion detector according to claim 4, wherein said feedback network loads the output of said first common emitter amplifier relatively lightly when said first integrator is storing less than a predetermined charge but abruptly changes to load said output relatively heavily when the charge stored in said first integrator exceeds a predetermined charge.

Claim 8

An ultrasonic motion detector according to claim 4, wherein said feedback network is a current sink which draws current from the output of said first common emitter amplifier in direct proportion to the charge stored in said first integrator.

Claim 9

An ultrasonic motion detector according to claim 5, wherein said active filter comprises a third common emitter amplifier having its input coupled to the output of said saturation amplifier; an emitter follower having its input coupled to the output of said third common emitter amplifier; and a twin-T filter having its input coupled to the output of said emitter follower and having its output fed back to the input of said third common emitter amplifier.

Claim 10

An ultrasonic motion detector device which receives an ultrasonic acoustic wave radiated into a space to be protected at an essentially constant carrier frequency and amplitude and which produces an alarm signal when the modulations of a received wave are characteristic of an alarm condition, comprising: A. means for producing an electrical signal which is representative of the amplitude modulations of a received ultrasonic wave; B. a saturation amplifier for producing an alternating signal in response to said electrical signal, having a frequency corresponding to the frequency of said electrical signal, the excursions of which have a first amplitude whenever said electrical signal exceeds a predetermined reference amplitude and have a second amplitude less than said first amplitude whenever said signal is less than said predetermined reference amplitude; C. an active filter for passing said alternating signal as an output signal having a frequency, the periodicity of which is within a predetermined pass-band, said pass-band having a lower limit which will reject turbulence type signals and an upper limit which will reject environmental signals like those of a ringing telephone; and D. an alarm and indicator circuit for producing an alarm in response to said output signal, corresponding to a train of said first amplitude alternating signal excursions occurring within a predetermined time.

Claim 11

An ultrasonic motion detector device which receives an ultrasonic acoustic wave radiated into a space to be protected at an essentially constant carrier frequency and amplitude and which produces an alarm signal when the modulations of a received wave are characteristic of an alarm condition, comprising: A. means for producing an electrical signal which is representative of the amplitude modulations of a received ultrasonic wave; B. a saturation amplifier for producing an alternating signal in response to said electrical signal, having a frequency corresponding to the frequency of said electrical signal, the excursions of which have a first amplitude whenever said electrical signal exceeds a predetermined reference amplitude and have a second amplitude less than said first amplitude whenever said signal is less than said predetermined reference amplitude; C. an active filter for passing said alternating signal as an output signal having a frequency, the periodicity of which is within a predetermined pass-band, said pass-band having a lower limit which will reject turbulence type signals and an upper limit which will reject environmental signals like those of a ringing telephone; and D. an alarm and indicator circuit for producing an alarm in response to said output signal, corresponding to a train of said first amplitude alternating signal excursions occurring within a predetermined time.