Intrusion alarm system with turbulence compensation

Claim 2

In an intrusion alarm system, means for radiating a signal at a predetermined frequency into a space, means for receiving the signal as it is reflected from objects within the space, the received signal having a frequency differing from that of the radiated signal by amounts corresponding to the rates of movement of said objects, means for combining the received and radiated signals to produce a difference signal having a frequency spectrum corresponding to differences in the frequencies of the radiated and received signals, bandpass filter means connected for filtering the difference signal and passing a frequency range centered in the higher portion of the frequency spectrum of the difference signal, turbulence compensation means comprising a pair of tuned voltage multipliers connected for receiving the signal from said filter means and producing voltages of opposite polarities having magnitudes corresponding to the amplitudes of the components at different frequencies in the output of said filter, and means for combining the outputs of said voltage multipliers to produce a signal corresponding to the components in the filter output.

Claim 3

An intrusion alarm system as in claim 1 wherein the means for combining the received and radiated signals includes a mixer comprising an operational amplifier having inverting and noninverting input terminals and an output terminal, the radiated and received signals being applied to the input terminals of said operational amplifier for producing the difference signal at said output terminal.

Claim 4

In an intrusion alarm system, means for radiating a signal at a predetermined frequency into a space, means for receiving the signal as it is reflected from objects within the space, the received signal having a frequency differing from that of the radiated signal by amounts corresponding to the rates of movement of said objects, means for combining the received and radiated signals to produce a difference signal having a frequency spectrum corresponding to differences in the frequencies of the radiated and received signals, bandpass filter means connected for filtering the difference signal and passing a frequency range centered in the higher portion of the frequency spectrum of the difference signal, turbulence compensation means connected for receiving the filtered signal and producing a compensated signal dependent upon the amplitude and duration of the filtered signal, and alarm means connected to be actuated in response to said compensated signal, said turbulence compensation means including first and second oppositely phased voltage doublers each driving its input from the output of said bandpass filter means and each including a timing capacitor connected at its output, said timing capacitors being of different values so that the oppositely polarized outputs of said voltage doublers rise at different rates corresponding to different frequencies in the filtered signal, and summing means connected to the outputs of said voltage doublers for producing a signal having a magnitude and polarity dependent upon the relative amplitudes of the different frequencies in the filtered signal.

Claim 5

In an intrusion alarm system, means for radiating a signal at a predetermined frequency into a space, means for receiving the signal as it is reflected from objects within the space, the received signal having a frequency differing from that of the radiated signal by amounts corresponding to the rates of movement of said objects, means for combining the received and radiated signals to produce a difference signal having a frequency spectrum corresponding to differences in the frequencies of the radiated and received signals, bandpass filter means connected for filtering the difference signal and passing a frequency range centered in the higher portion of the frequency spectrum of the difference signal, turbulence compensation means connected for receiving the filtered signal and producing a compensated signal dependent upon the amplitude and duration of the filtered signal, and alarm means connected to be actuated in response to said compensated signal, said turbulence compensation means including first and second oppositely phased voltage doublers each driving its input from the output of said bandpass filter means and each including a timing capacitor connected at its output, said timing capacitors being of different values so that the oppositely polarized outputs of said voltage doublers rise at different rates corresponding to different frequencies in the filtered signal, and summing means connected to the outputs of said voltage doublers for producing a signal having a magnitude and polarity dependent upon the relative amplitudes of the different frequencies in the filtered signal.

Claim 6

An intrusion alarm system as in claim 3 wherein said voltage doublers include series connected input resistors of different values so that signals of long duration and having a magnitude above a predetermined level will produce a signal sufficient for actuating said alarm means.

Claim 7

An intrusion alarm system as in claim 3 together with integrator means connected for receiving the signal from said summation means and delaying activation of said alarm means until said signal remains above a predetermined level for a predetermined period of time.

Claim 8

An intrusion alarm system as in claim 1 wherein said alarm means is normally maintained in a deenergized condition by normally energized means connected in series with first and second normally conducting switching means, said first switching means being controlled by the signal from said compensator means and said second switching means being controlled by said radiated signal so that interruption of said radiated signal causes energization of said alarm means.

Claim 9

An intrusion alarm system as in claim 1 wherein the means for receiving the reflected signal includes an operational amplifier having inverting and noninverting input terminals across which the reflected signal is applied, said operational amplifier providing means for passing said reflected signal and rejecting signals which appear in phase on each of the input terminals.

Claim 10

In an intrusion detector system of the type including means for comparing the frequencies of radiated and reflected signals to produce an alarm signal having a frequency dependent on the difference in the frequencies of said radiated and reflected signals, said difference depending upon the rate of movement in a protected space, means for distinguishing between movements of an intruder and other movements such as air turbulence, said last-named means including a bandpass filter connected for filtering the alarm signal to pass a band of frequencies centered at a frequency on the order of 40 hertz, a pair of tuned voltage doublers connected for receiving the output of said bandpass filter and producing voltages of opposite polarities having magnitudes corresponding to the amplitudes of the components at different frequencies in the output of said filter, summing means connected to the outputs of said voltage doublers for producing a signal having a magnitude and polarity dependent upon the relative amplitudes of the components in the filter output.

Claim 11

In an intrusion detector system of the type including means for comparing the frequencies of radiated and reflected signals to produce an alarm signal having a frequency dependent on the difference in the frequencies of said radiated and reflected signals, said difference depending upon the rate of movement in a protected space, means for distinguishing between movements of an intruder and other movements such as air turbulence, said last-named means including a bandpass filter connected for filtering the alarm signal to pass a band of frequencies centered at a frequency on the order of 40 hertz, a pair of tuned voltage doublers connected for receiving the output of said bandpass filter and producing voltages of opposite polarities having magnitudes corresponding to the amplitudes of the components at different frequencies in the output of said filter, summing means connected to the outputs of said voltage doublers for producing a signal having a magnitude and polarity dependent upon the relative amplitudes of the components in the filter output.