The circuit is preferably located within an area that is to be secured, is of the type that transmits an ultrasonic signal to establish an ultrasonic wave pattern in the area, and includes doppler phase detection circuitry responsive to both the transmitted and received ultrasonic signals for providing a doppler signal of a frequency corresponding to the velocity of motion in the area. In one embodiment the circuit includes a threshold filter and a detection filter each having different frequency responses, both coupling to separate inputs of a differential detector, an output accumulator circuit coupled from the differential detector, and a high pass filter for inhibiting the output accumulator circuit upon receiving signals of above a predetermined frequency, but inhibiting the accumulator for only up to a preselected time interval. In another embodiment of the invention the circuit includes, in addition to a threshold filter, detection filter, differential detector, and output accumulator circuit, a separate cancel channel and associated receiver transducer responsive preferably to higher frequency noise signals at frequencies just below the frequency of the transmitted ultrasonic signal to inhibit the output accumulator upon receipt of such signals but only for a preselected time interval.
An intrusion alarm of the kind in which a radiation field is transmitted in an area to be supervised; the reflected field is received and compared with the transmitted field, and a comparison signal is produced the frequency of which is indicative of the speed of movement of an object in the supervised area. A signal processor receives the comparison signal and generates an alarm if the comparison signal contains components in a selected frequency range. The processor includes a unique filter block which removes unwanted frequency components outside the range. The filter block includes a pulse generator which generates a constant amplitude pulse train, each pulse corresponding to a pulsation of the comparison signal, and control elements which control the duty cycle of the pulse train so that as the frequency of the comparison signal increases, the average level of the pulse train first increases and then decreases. The pulse train is integrated and operates an alarm signal generator when its average level rises above a preselected level.
To detect breakage of glass panes, panels of display cases, or movement in a room, ultrasonic waves, preferably in the order of from 120 kHz to 180 kHz, are transmitted to the sonically conductive medium (glass panes, plastic sheets, or into the air of the room), and the waves are received in a receiver. The time shift of the received waves at the receiver location, with respect to the transmitted waves is determined, and if this time shift changes beyond a predetermined limit, an alarm signal is generated. Preferably, the ultrasonic signals are frequency modulated, for example by shifting the generated waves by a predetermined frequency shift, and determining the temporal change, or delay of the frequency shift, as received, with respect to the time of frequency shift at the transmitter. To prevent the effect of drift, the rate of change of received with respect to transmitted frequency shift can be used to generate the alarm.
The invention relates to a motion detector or proximity switch for detecting moving objects, wherein a high frequency electromagnetic radiation is generated by a free running oscillator and transmitted via a transmitter antenna. The transmitter antenna detects the Doppler modified radiation reflected by the moving object as a function of its phase position or amplitude variation. The radiation is compared with the transmitted radiation parameters in an evaluation device with a view to producing an output signal. The inventive detector is characterized in that it included a free running oscillator having a feedback guaranteed by at least one transmitter antenna ANT RX and at least one receiver antenna ANT TX which are oriented towards the object and coupled via a side or leakage radiation.
In a system for the remote control of premises using a watch radar apparatus for detecting intrusions into its field of radiation, including an alarm device, wherein the reception by the radar apparatus of radiation from portable transmitting device controls the connection of the radar apparatus to the alarm device, so that the alarm is made to change from an operative state to an inoperative state, and to change from an inoperative state to an operative state in response to the actuation of said portable transmitting device.
Composite noise and information signals are amplified and filtered to segregate high and low frequency bands that correspond with noise from an intermediate frequency band which corresponds with the information signal. The absolute values of the two noise band signals are summed, weighted, and compared with the information band signal in an operational amplifier whose output tends toward a signal of one polarity with respect to a reference voltage due to noise and tends toward the opposite polarity due to the information band frequency. The signal is integrated and used to control an alarm circuit and environmental noise indicating devices. Means are provided to reduce sensitivity of one of the devices in the presence of high noise and to restore sensitivity if a valid information signal occurs. The other device is used to warn of persistent environmental noise that might be eliminated. The input amplifier of the system is provided with a feedback circuit that brings about compressor action to null the effect of high transient noises.
