Title:
DUAL ALARM, COAXIAL LINE RESONATOR, INTRUSION DETECTION SYSTEM
United States Patent 3599195
Abstract:
An alarm system having at least one condition responsive sensor. A plurality of sensors can be employed in the system to detect such conditions as the presence of a moving intruder within a protected area, heat and/or smoke, the movement of windows and doors, the presence or absence of infrared and/or visible radiation, and any other condition that can be monitored by sensing means. The system preferably includes a logic circuit that is programmed to respond to the output signals from one or more preselected sensors. At least one timer is used to actuate a first alarm device in response to a first alarm signal from one or more of the condition responsive sensors. If a second alarm signal occurs within a predetermined period of time after the first alarm signal, a second alarm device is actuated. The timer is reset if the second alarm signal does not occur within the predetermined time period. False alarm signals are minimized by inhibiting the second alarm portion of the timer for a short interval after the first alarm signal and at the end of each full timing cycle. The alarm system employs full solid-state circuitry and has a standby DC power capability.
US Patent References:
Coin-controlled vehicle parking system
Allstadt, Jr. - December 1952 - 2623933
Seismic personnel sensor
Stetten et al. - July 1966 - 3261009
TIMING DEVICE WITH OPTIONAL SIGNAL
Ebner - December 1969 - 3484769
QUALITY CONTROL CIRCUIT HAVING TIMER CONTROLLED SIGNALS
Kamberg et al. - April 1970 - 3508242
Speed measuring apparatus for railroad classification yards
Auer, Jr. et al. - November 1958 - 2859434
Coin-controlled vehicle parking system
Allstadt, Jr. - December 1952 - 2623933
Seismic personnel sensor
Stetten et al. - July 1966 - 3261009
TIMING DEVICE WITH OPTIONAL SIGNAL
Ebner - December 1969 - 3484769
QUALITY CONTROL CIRCUIT HAVING TIMER CONTROLLED SIGNALS
Kamberg et al. - April 1970 - 3508242
Speed measuring apparatus for railroad classification yards
Auer, Jr. et al. - November 1958 - 2859434
Application Number:
04/733671
Publication Date:
08/10/1971
Filing Date:
05/31/1968
View Patent Images:
Export Citation:
Assignee:
Pinkerton's Incorporated (New York, NY)
Primary Class:
Other Classes:
340/309.160, 340/309.800, 340/521, 340/309.300, 334/45
International Classes:
G08B13/24; G08B19/00; G08B25/14; H03F3/60; G08B13/22; G01S9/44
Field of Search:
340/258,258A,258C,213,213.1,261,309.1,309.3 343/8 334/45
US Patent References:
| 3158850 | Burglar alarm system | November 1964 | Pozranski | |
| 3210752 | Moving object detection system | October 1965 | Bojko | |
| 3234534 | Fault alarm display systems | February 1966 | Todman | |
| 3270292 | Ultra high frequency transistor oscillator | August 1966 | Harwood | |
| 3380044 | UNIVERSAL-SENSOR CONTROL SYSTEM | April 1968 | Mordwinkin | |
| 3440650 | DOPPLER SYSTEM OSCILLATOR CIRCUIT | April 1969 | Kimball | |
| 3447145 | CONSTANT SURVEILLANCE ALARM SYSTEM FOR A PLURALITY OF REMOTE LOCATIONS | May 1969 | Schumann |
Primary Examiner:
Caldwell, John W.
Assistant Examiner:
Palan, Perry
Claims:
What I claim and desire to secure by Letters Patent of the United States is
1. A condition responsive alarm system comprising:
2. A condition responsive alarm system comprising:
3. The alarm system of claim 2 further characterized by first and second alarm means responsive to said first and second alarm signals, respectively.
4. The alarm system of claim 2 further characterized by a plurality of motion sensors and logical OR circuit means for connecting the output signal producing means of said sensors to said timer.
5. The alarm system of claim 2 further characterized by a second plurality of motion sensors and second logical OR circuit means for connecting the output signal producing means of said second plurality of sensors to a second sequential, dual alarm timer means.
6. A condition responsive alarm system comprising:
1. A condition responsive alarm system comprising:
2. A condition responsive alarm system comprising:
3. The alarm system of claim 2 further characterized by first and second alarm means responsive to said first and second alarm signals, respectively.
4. The alarm system of claim 2 further characterized by a plurality of motion sensors and logical OR circuit means for connecting the output signal producing means of said sensors to said timer.
5. The alarm system of claim 2 further characterized by a second plurality of motion sensors and second logical OR circuit means for connecting the output signal producing means of said second plurality of sensors to a second sequential, dual alarm timer means.
6. A condition responsive alarm system comprising:
Description:
CROSS-REFERENCES TO RELATED APPLICATIONS
The subject matter of the present application is related to the "Electromagnetic Moving Object Detection System Utilizing A Coaxial Line Resonator and the Plural Chambered, Oscillator-Coaxial Line Resonator-Detector Assembly for Moving Object Detection Systems" described in my copending applications Ser. No. 733,673, filed May 31, 1968, and Ser. No. 733,672 filed May 31, 1968, respectively.
BACKGROUND OF THE INVENTION
The present invention relates to alarm systems in general and, more particularly, to a continuous wave, electromagnetic moving object detection system which senses changes in the impedance of the system's antenna circuit produced by an object moving through the protection area. Provision is made in the system for utilizing the timing and alarm circuits on a shared basis with other condition responsive sensors to broaden the type of protection coverage provided by the alarm system.
Moving object detection systems of the general type are familiar to those skilled in the detection art. Representative examples of such systems include Chapin, U.S. Reissue Pat. No. 25,100 and Bojko, U.S. Pat. Nos. 3,210,752 and 3,237,191. A number of the prior art systems employed one or more remote antennas that were driven by a corresponding number of oscillators located in a central control station. In some instances, a single oscillator was used to drive a pair of antennas. However, in each instance the electrical connections between the remote antennas and the central station oscillators were made by coaxial cable. This wiring arrangement presented a number of problems including, signal attenuation along the coaxial cables, false alarms produced by motion of the cable, high cable and installation costs, and maintenance of the cable and connectors.
In the above-mentioned copending applications, there is described a continuous wave oscillator-coaxial line resonator-detector circuit and assembly for electromagnetic moving object detection systems. The use of a high Q, coaxial line resonator provides increased sensitivity at reduced power levels, effectively isolates the oscillator circuit from impedance changes in the antenna circuit and reduces interferences from spurious transmissions. Detection of changes in the antenna circuit impedance is performed, in one embodiment, by a crystal rectifier connected to the center conductor of the coaxial line resonator. One of the advantages of this circuit is that the electrical components for signal generation, transmission, reception and detection comprise a single physical entity or unit. If the motion sensing unit is placed at a remote location, ordinary wiring can be used for the power supply and the alarm signal circuits between the remote unit and the central control station.
The protection of large areas against moving intruders normally requires a plurality of remote sensing units each connected to a central control station. It is desirable in large area protection systems to have zone coverage and zone identification of the motion alarm signals. In addition, identification of and discrimination against false alarms should be provided by a system of plural, sequential alarms.
Accordingly, it is a general object of the present invention to provide an alarm system having at least one remote motion sensing unit and a central control station.
It is a specific object of the invention to provide an alarm system having a central control station and at least one remote motion sensor comprising a continuous wave oscillator, a coaxial line resonator, a radiator, and a detector.
It is a feature of the invention that ordinary wiring can be employed for the power supply and alarm signal circuits between the control station and each remote sensor.
It is another feature of the invention that amplification of the detected motion signal can be performed at each remote sensor.
It is another object of the invention to provide a timed, sequential dual alarm. It is a feature of the dual alarm circuit that the circuit is blocked for a predetermined period of time after the first alarm signal and at the end of each full alarm cycle.
It is still another object of the invention to provide an alarm system that will accommodate alarm signals from other condition responsive sensors.
It is a further object of the invention to provide a plural sensor moving object detection system that provides zone coverage and zone alarm identification.
These objects and other objects and features of the present invention will best be understood from a detailed description of a preferred embodiment thereof, selected for purposes of illustration, and shown in the accompanying drawings, in which:
FIG. 1 is a block diagram of the alarm system showing the major components thereof;
FIG. 2 is a schematic diagram of one of the motion sensors;
FIG. 3 is a schematic diagram of the alarm signal amplifier;
FIG. 4 is a schematic diagram of one of the logic circuit gates;
FIG. 5 is a schematic diagram of the sequential, dual alarm timer;
FIG. 6 is a block diagram of one configuration of the logic circuit with a plurality of remote motion sensors; and,
FIG. 7 is a schematic diagram of the line-battery power supply for the alarm system.
Turning now to the drawings, and particularly to FIG. 1 thereof, there is shown in block diagram form an alarm system constructed in accordance with the present invention and indicated generally by the reference numeral 10. The alarm system has at least one electromagnetic moving object detector or sensor 12 comprising a radio frequency oscillator 14, a coaxial line resonator 16, an antenna 18 and a detector 20 for sensing changes in the antenna circuit impedance produced by objects moving within the radiated field pattern in the protected area.
The motion or "alarm" signal is amplified by amplifier 22 and the amplified signal is then fed either to a logic circuit 24 or directly to timer 26. The output signal from the logic circuit is applied to timer 26 or timer 28 in accordance with the logic circuit prewiring. Upon receipt of the alarm signal, timer 26 actuates a first alarm 30 and initiates a timing period of predetermined length. If a second motion or "alarm" signal is produced by motion sensor 12 within the timing period, the timer actuates a second alarm 32. However, if a second alarm signal does not occur within the predetermined period, the timer is reset. An inhibit circuit 34 is provided to block the timer from any alarm signal for a short period after receipt of the first alarm signal and again at the end of the timing cycle. The latter inhibiting of timer 26 eliminates the problem of "ride through" at the end of the timing cycle. Corresponding first and second alarms 36 and 38, respectively, and an inhibit circuit 40 are connected to timer 28.
If more than one remote moving object sensor 12 is used in the alarm system, the output "alarm" signals from the sensors are fed to the logic circuit 24 for processing to one or more of the timers. The additional remote sensors and signal amplifiers are represented as a group 42 by the dashed block in FIG. 1.
The alarm system 10 can accommodate a variety of satellite sensors to provide coverage of other conditions besides the presence of a moving intruder within the protected area. For instance, a heat and/or smoke sensor 44 can be positioned at a critical location with the output from the sensor being directly fed to one of the timers 26 and 28 or alternatively to the logic circuit 24. The latter configuration provides greater interconnection flexibility together with area identification. Additional condition responsive sensors or switches, representationally indicated by block 46 can be wired into the alarm system to share the logic, timer and alarm circuits.
Power for the alarm system 10 is provided by a line operated power supply 48 that has standby DC power capability. Plural stage voltage regulation is used in the power supply and at the RF oscillator 14 to maintain stable operation of the alarm system.
Having briefly discussed the major components of the alarm system, I will now describe in detail the circuitry of the electromagnetic motion sensor 12, amplifier 22, logic circuit 24, timers 26 and 28, and the power supply 48.
ELECTROMAGNETIC MOTION SENSOR
The motion sensor portion of the alarm system is shown in schematic form in FIG. 2. The tunable RF oscillator 14 employs a single, grounded base NPN transistor 50 to generate the continuous, sinusoidal waves that excite a coaxial line resonator 52. A typical operating frequency for oscillator 20 is 400 megahertz. However, other frequencies, generally in the UHF range, can be used for electromagnetic motion detectors. RF ground for the base of transistor 50 is established by a capacitor 54 that shunts base resistor 56. The base resistor 56, together with resistor 58 forms a bias voltage divider from B + regulated to ground. Emitter resistor 60 provides a DC feedback path for oscillator stabilization while RF feedback is prevented by a shunt capacitor 62 which places a RF ground at the bottom of radio frequency choke 64. Coupling of the generated radio frequency energy to the power supply (not shown) is prevented by a second radio frequency choke 66 in the collector circuit.
The required inphase RF feedback to sustain oscillation is provided by the collector-base and emitter-base capacitances. The frequency determining components of the oscillator comprise inductor 68, variable capacitor 70 and a portion of the coaxial line center conductor 72. The oscillator frequency is tuned by varying the series capacitance of the frequency determining circuit. This is accomplished by adjusting the variable capacitor 70.
The oscillator circuit 14 is shielded by an electromagnetic shield shown by the dashed lines in FIG. 2 and identified by the reference numeral 74. Preferably, the oscillator circuit and coaxial line resonator 52 are constructed on a common chassis so that a portion of the oscillator shield 74 is common to the coaxial line resonator outer conductor 76. However, if the oscillator circuit and the coaxial line resonator are physically separated, a current return path must be provided as shown by line 78.
Coaxial line resonators of the type illustrated in FIG. 2 are now generally classified as "cavity" resonators. Henney, Radio Engineering Handbook, 5th Edition, page 6--46. Conceptually, the coaxial line resonator 16 can be regarded as a coaxial transmission line short-circuited at one end and open at the other end. Terman, Electronic and Radio Engineering, 4th Edition, pages 159--161. In the present embodiment, the coaxial line resonator is capacitively loaded and tuned by a variable capacitor 80 located at the open end of the line. This location provides the greatest tuning effect per unit of capacitance. However, other tuning methods, including varying the physical dimensions of the "cavity," can be employed to "peak" the coaxial line resonator.
Physically, the coaxial line resonator or cavity can have a true coaxial construction, i.e., inner and outer cylindrical conductors with a common axis, or a hybrid configuration. One possible hybrid configuration is the so-called "trough line" that has a center conductor positioned within a rectangular prism cavity. The same circuit concepts and tuning techniques are applicable to both the cylindrical and rectangular configurations. However, from the standpoint of mechanical fabrication, production line assembly, and component mounting, the rectilinear configuration is preferable. Construction details of the rectilinear "coaxial line" resonator are illustrated in my above-mentioned copending application for Plural Chambered, Oscillator-Coaxial Line Resonator-Detector Assembly for Moving Object Detection Systems.
The term "coaxial line" has been selected to describe the resonator 52 because it connotes a centrally disposed conductor surrounded by one or more conducting surfaces. This is true even though the conducting surfaces may define a rectangular cavity rather than a cylindrical cavity. Therefore, as used herein, the term "coaxial line resonator" shall mean a resonant cavity having a centrally disposed conductor short-circuited at one end to the conducting surface or surfaces which form the cavity and open at the other end.
The coaxial line resonator 52 has a high Figure of Merit (Q) which allows the oscillator 14 to be very loosely coupled to the resonator. Coupling of the oscillator to the resonator is controlled by the position of the oscillator tap point 82 along the center conductor 72 of the resonator. The coupling should be as loose as possible within the limits imposed by the desired detection range. The loose coupling of the oscillator to the high Q coaxial line resonator circuit effectively isolates the oscillator from motion produced impedance changes in the antenna circuit thereby maintaining the frequency stability of the oscillator.
The coaxial line resonator 52 is constructed with the center conductor 72 having a physical length that is less than one-fourth λ at the operating frequency. The electrical length of the line is adjusted by varying capacitor 80. The output from the coaxial line resonator is capacitively coupled through capacitor 84 to radiator 18. The radiator, which has a length between one-fourth λ and one-half λ, is voltage fed to achieve maximum detection sensitivity. It can be seen from FIG. 2, that the output from the coaxial line resonator is taken at a point 86 which is very close to the point of maximum voltage on the center conductor 72.
Changes in the impedance of the antenna circuit produced by motion of an object within the radiated field pattern of the alarm system are sensed by a rectifier 88. The rectifier is connected to the centerline 72 of the coaxial line resonator at a point 90 located slightly below the output tap 86 for the antenna. The connection point for the rectifier is a compromise between achieving maximum voltage output and minimum effect upon the Q of the coaxial line resonator. A load for the rectifier 88 is provided by resistor 92.
It will be appreciated that in the absence of a moving object, a steady state DC level will be established at the junction of the rectifier 88, load resistor 92 and coupling capacitor 94. When an object moves within the radiated field pattern, the reflected and transmitted energy combine in the antenna circuit to produce a new voltage-current ratio or impedance. Fluctuations in amplitude and phase of the combined signals occur as the object moves through the radiated field pattern. These fluctuations produce an alternating current at the output of the rectifier which rides on the steady state DC voltage. The alternating current or "alarm signal" is coupled through capacitor 94 to amplifier 22.
AMPLIFIER
Referring to FIG. 3, the alarm system employs a high gain, low frequency amplifier 22 to boost the detected motion signal to a level that is sufficient for processing in the logic circuit 24 and subsequent actuation of timers 26 and 28. The amplifier is designed to have a gain of unity at DC and a gain of 2500 at 1.0 hertz with a bandwidth of 0.5 hertz to 3.0 hertz (3 db. points).
The circuitry of amplifier 22 is relatively straight-forward and need not be explained in detail in order to understand the alarm system of the present invention. A high impedance, input stage is provided by a field effect transistor (FET) 96 connected as a source follower to the first stage of a two stage, direct coupled amplifier comprising transistors 98 and 100. The FET input stage allows the use of a much smaller value of capacitance for the coupling capacitor 94. In view of the low frequency bandwidth of the amplifier, this feature is important in terms of the physical size of the coupling capacitor.
Amplification of the detected motion signal is performed by the two stage amplifier circuit of transistors 98 and 100. The bandwidth of the total circuit, i.e., FET 96 and transistors 98 and 100, is determined at the high end by capacitor 102 in the Gate circuit of FET 94 and by a collector-to-base feedback capacitor 104 for transistor 100. The value of the feedback capacitor is selected to provide high frequency clipping over 30.0 hertz and at 35.0 hertz, the gain of the amplifier is unity. The low end of the amplifier bandwidth is controlled by the first stage emitter resistor and capacitor 106 and 108, respectively, and by the corresponding resistor 110 and capacitor 112 in the emitter circuit of the second stage transistor 100.
Two operating controls are provided in amplifier 22: a Linearity control 114 and a Range control 116. Normally, the Linearity control is a factory adjustment that is made to increase or decrease the current flow through the first stage transistor 98 to match the individual characteristics of the input stage field effect transistor 96. The Range control 116 adjusts the gain of amplifier 22 by increasing or decreasing the amount of unbypassed feedback resistance in the emitter circuit of transistor 100. The maximum gain and therefore the maximum range for the motion sensor 12 is obtained when the Range control is set for minimum resistance.
LOGIC GATE
The logic circuit 24 shown in block diagram in FIG. 1 comprises one or more logic gates 118 depicted in schematic diagram in FIG. 4. The output from amplifier 22 is capacitively coupled through capacitor 120 to the base of a normally cutoff transistor 122. The presence of the amplified motion signal at the base of transistor 122, biases the transistor into conduction causing a positive going pulse to be applied to the input of timer 26.
For the present, it is sufficient to note that in a plural sensor system, each remote motion sensor 12 has its own amplifier 22 and logic gate 120 and that two or more of the gates can be prewired with their collectors in parallel to form an OR input circuit for one of the timers. In each case, the prewired parallel gates use a common collector load resistor 124 which is shown in the timer input circuit in FIG. 5.
TIMER
The basic function of the electronic timer 26 is to provide sequential, dual alarm signals to the first and second alarm means 30 and 32, respectively. In order to minimize the possibility of false alarms produced by switching transients and other nonalarm signals, the first alarm control circuitry of the timer is gated for a short period after the first alarm and at the end of each full timing cycle.
The specific circuitry which performs these functions is illustrated in the schematic diagram of FIG. 5. The timer 26 comprises two bistable devices, such as, flip-flops (FF) 126 and 128, two alarm relays 130 and 132 and the associated trigger and gating circuits which will be described below in detail. The energization state of the first alarm relay 130 is controlled by FF 126 while the second alarm relay 132 is energized or deenergized by the action of FF 128. Each flip-flop has two transistors, one normally conducting and the other normally cutoff. For flip-flop 126, transistor 126a is normally conducting and transistor 126b is normally cutoff. Similarly, for flip-flop 128, transistor 128a is normally ON while transistor 128b is normally OFF.
The operation of timer 26 can best be understood by examining the sequence of events produced by the presence of a moving object within the radiated field pattern of the motion sensor 12. The motion of the object through the protected area causes changes in the antenna circuit impedance which generate an AC motion signal at the output of rectifier 88 (FIG. 2). The alternating current motion signal is capacitively coupled to and amplified by the low frequency, high gain amplifier 22. After amplification, the motion signal is capacitively coupled to the base of the normally cutoff logic gate transistor 122. The motion signal forces transistor 122 into conduction causing a positive going pulse to be applied through crystal diode 134 to the base of the normally OFF flip-flop transistor 126b.
Transistor 126b turns ON thereby turning OFF the normally conducting transistor 126a. When transistor 126a stops conducting the first alarm relay 130 deenergizes and actuates the first alarm 30. Various wiring options are available for the first alarm 30 because the first alarm relay 130 has both normally closed and normally open contacts, 130a--130b and 130a--130c, respectively. As shown in FIG. 5, the relay is normally energized and it is assumed that the first alarm 30 is actuated by the closure of the normally open contacts 130a--130c upon deenergization of the relay.
When the normally conducting transistor 126a stops conducting, the power supply voltage appears at the collector of transistor 126a. At this moment, capacitor 136 starts to charge through the path established by resistors 138 and 140 and the coil of relay 130. The RC charge time for capacitor 136 is designed to provide a period of from 3 to 5 seconds before the voltage at the emitter of unijunction transistor (UJT) 142 reaches the firing point of the UJT.
The firing of the UJT trigger 142 applies a positive pulse through isolating crystal diode 144 to the base of the normally cutoff flip-flop transistor 128b causing the transistor to begin conducting. With transistor 128b conducting, transistor 128a is cutoff by the well-known flip-flop action. When transistor 128a stops conducting, the second alarm relay 132 drops out causing relay transfer contact 132a to move from the normally closed contact 132b to the normally open contact 132c.
The second alarm 32 is wired in parallel with the first alarm for closed circuit standby condition and in series for open circuit standby condition. At the very instant that the second alarm relay 132 deenergizes, the conditions for a second alarm are fulfilled. However, this condition is only momentary because of the action of the gating circuit which will be described below. A suitable delay circuit can be inserted in the second alarm circuit to completely eliminate even a momentary second alarm.
When relay 132 deenergizes, relay transfer contact 132d moves from fixed contact 132e to fixed contact 132f. This action puts B + voltage on one side of capacitor 146 causing the capacitor to charge through resistor 148. The positive voltage at the top of resistor 148 biases a normally cutoff field effect transistor (FET) 150 into conduction which in turn causes transistor 152 to conduct.
With transistor 152 conducting, the base of FF transistor 126a is biased almost to the supply voltage because of the relative resistances of resistor 154 and the series circuit of resistances 156 and 158. The resistor 154 has a very low value compared to the series resistance of resistors 156 and 158. For instance, a resistance ratio of approximately 1:50 is suitable to cause hard conduction of FF transistor 126a. This condition will last for one to two seconds while the FET 150 is biased into conduction by the voltage developed by the charging current of capacitor 146. During this period, the first alarm flip-flop 126 is gated against any input signal because even a positive alarm signal would not be sufficient to turn off the hard conducting FF transistor 126a. At the end of the 1--2 second period, FET 150 and transistor 152 stop conducting and FF transistor 126a returns to its normal conducting bias condition.
It should be noted that when FF transistor 126a was triggered into conduction by the FET 150-transistor 152 gating circuit, the first alarm relay 130 was also re-energized. The alarm relay will remain energized until the next alarm signal causes FF transistor 126a to stop conducting.
To recapitulate, at this point in the timer sequence, the first alarm relay is energized and the second alarm relay is deenergized. If another alarm signal is received within a predetermined time period, FF 126 is triggered causing relay 130 to drop out. Since the second alarm relay is already deenergized, the conditions are fulfilled for a second alarm and the second alarm 32 is actuated.
The predetermined time period within which the second alarm signal must occur is established by a trigger circuit comprising unijunction transistor (UJT) 160, capacitor 162 and resistor 164. When the second alarm relay 132 deenergizes, capacitor 162 starts to charge through the path established by resistor 164 and contacts 132d and 132f of the second alarm relay. The RC time constant is selected so that the firing voltage for UJT 160 is reached approximately one minute after the second alarm relay was deenergized. Firing of the UJT trigger 160 puts a positive pulse through isolating crystal diode 166 on the base of FF transistor 128a causing the transistor to start conducting again.
The second alarm relay 132 is again energized and the short circuit across capacitor 168 is removed by the transfer of relay contact 132d from contact 132f to contact 132e. Capacitor 168 functions in the same manner as capacitor 146 by charging through FET gate resistor 148. Both the FET and transistor 142 are turned on causing FF transistor 126a to conduct hard for another 1--2 second period. The gating of the first alarm flip-flop at the end of each full timing cycle is done to prevent any possibility of timer "ride through" caused by switching transients.
A conventional tamper switch 170 is provided for the alarm system to give a warning of any physical disturbance to the system. Opening of the normally closed tamper switch 170 breaks the emitter circuit for FF transistor 126a causing relay 130 to drop out which in turn actuates the first alarm 30.
A key switch 172 is also provided in the alarm system to prevent alarms during normal business hours or at any other time selected by the user. The key switch 172 is normally closed in the ALARM condition. When the switch is opened for STANDBY operation, resistor 174 is added to the gate circuit of FET 150 and, together with resistor 176, forms a voltage divider from B + to ground. FET 150 is biased ON by the voltage divider and remains conducting as long as the key switch is open. Since FET 150 is conducting, transistor 152 will also be conducting with the result that FF transistor 126a will conduct hard until the key switch is closed. In this condition, it is impossible to turn OFF FF transistor 126a with any alarm signal that is applied to the base of FF transistor 126b.
LOGIC CIRCUIT
In an alarm system having a plurality of remote motion sensors 12, and a corresponding plurality of amplifiers 22, a variety of interconnection configurations can be employed to provide the desired degree of zone coverage and zone identification of alarm signals. Given an eight sensor system, the interconnection arrangements can vary from eight sensors driving eight amplifiers and eight gates 118 that are logical OR connected, or at the opposite pole, each sensor-amplifier can have its own separate timer. It will be appreciated that the alarm system of the present invention is not limited to any specific interconnection configuration and that in the simplest form, the system can comprise a single motion sensor driving an amplifier which in turn is connected to a single, sequential dual alarm timer that actuates the first and second alarms.
One representative example of an eight sensor interconnection arrangement is illustrated in block diagram in FIG. 6. Of the eight motion sensors, four sensors 12a through 12d are connected through their corresponding amplifiers 22 and gates 118 to a single timer 26 a--d so that a motion signal from any one of the four sensors will actuate the timer. The logical OR function is performed by prewiring the output collector circuits of the gates in parallel to a common load resistor, such as, resistor 124 shown in the timer diagram of FIG. 5. Two of the remaining sensors, 12e and 12f, are prewired in an OR configuration to another timer 26e--f. The last two sensors, 12g and 12h each have their own individual timers, 26g and 26h, respectively.
Other configurations can be employed to meet the particular characteristics of the protection environment. It has been found that a Four-Two-Two sensor configuration with three timers is practical and has a good degree of flexibility.
The separate sensor-timer arrangements are useful when specific zone coverage and zone identification are required. For instance, the four OR wired motion sensors 12a through 12d could be used for perimeter zone protection while the single separate sensors could be used in one or more areas requiring maximum security.
POWER SUPPLY
The basic line-battery operated power supply 48 has two stages of voltage regulation as shown in FIG. 7. A third stage of voltage regulations is provided for the RF oscillator 14 to compensate for voltage drops in the wiring between the central station power supply and the remotely located motion sensor oscillator. The circuitry for the third stage regulator is shown in the amplifier schematic of FIG. 3 and will be discussed later on.
Referring now to FIG. 7, the power supply 48 comprises: a standby, rechargable battery 178; a line operated, full wave rectifier 180; a first stage series voltage regulator 182; a battery charger and control circuit 184; a second stage series voltage regulator 186; and, a zener referenced, four stage DC amplifier control circuit 188 for the second stage regulator 186.
In normal operation, the alarm system circuits are powered by the rectified line current. Battery 178 is provided for standby DC power in the event of power line failures. The battery is maintained in a charged condition by battery charger 184 that utilizes a control transistor 190 to vary the base current of the series regulator 182. A voltage reference for the control transistor 190 is established by a single field effect transistor (FET) 192. Another field effect transistor 194, connected as a source follower, is interposed between the voltage reference transistor 192 and the control transistor 190 to act as a buffer.
Short circuit protection for battery 178 is provided by a circuit breaker 196. Protection for the line operated supply is obtained by cutting off both the series regulator 182 and the control transistor 190 whenever the current drain exceeds a predetermined amount. The series regulator 182 is cutoff by diode 198 when the voltage drops across resistor 200 and the base-emitter junction of regulator 182 exceeds the forward voltage required to overcome the junction potential barrier of the diode. A similar action occurs in the control transistor 190 with respect to resistor 199 and the series diodes 201.
The second stage, series voltage regulator 186 is controlled by the four stage DC amplifier 188 that is referenced to Zener diode 202. If the motion sensor RF oscillators were located at the central station two stages of power supply regulation would normally be sufficient. However, the oscillators are usually located at a distance of up to 300 feet from the central station. At such distances the voltage drops in the connecting wire must be compensated for by an additional stage of voltage regulation at the oscillator itself.
In the preferred embodiment of the invention, the amplifier and RF oscillator are housed in the same unit so that load length between the amplifier assembly and the oscillator can be considered negligible from the standpoint of a voltage drop. Looking at the amplifier assembly schematic shown in FIG. 3, it can be seen that the output from the second stage power supply regulator is applied to a third stage regulator, indicated generally by the reference numeral 204. The third stage regulator comprises a series transistor regulator 206 and a central transistor 208 that is referenced to Zener diode 210. The regulated output from transistor 206 is used to power both the RF oscillator 14 and the amplifier 22.
Having described in detail the preferred embodiments of the alarm system, it will now be apparent to those in the art that numerous modifications can be made thereto without departing from the scope of the present invention.
The subject matter of the present application is related to the "Electromagnetic Moving Object Detection System Utilizing A Coaxial Line Resonator and the Plural Chambered, Oscillator-Coaxial Line Resonator-Detector Assembly for Moving Object Detection Systems" described in my copending applications Ser. No. 733,673, filed May 31, 1968, and Ser. No. 733,672 filed May 31, 1968, respectively.
BACKGROUND OF THE INVENTION
The present invention relates to alarm systems in general and, more particularly, to a continuous wave, electromagnetic moving object detection system which senses changes in the impedance of the system's antenna circuit produced by an object moving through the protection area. Provision is made in the system for utilizing the timing and alarm circuits on a shared basis with other condition responsive sensors to broaden the type of protection coverage provided by the alarm system.
Moving object detection systems of the general type are familiar to those skilled in the detection art. Representative examples of such systems include Chapin, U.S. Reissue Pat. No. 25,100 and Bojko, U.S. Pat. Nos. 3,210,752 and 3,237,191. A number of the prior art systems employed one or more remote antennas that were driven by a corresponding number of oscillators located in a central control station. In some instances, a single oscillator was used to drive a pair of antennas. However, in each instance the electrical connections between the remote antennas and the central station oscillators were made by coaxial cable. This wiring arrangement presented a number of problems including, signal attenuation along the coaxial cables, false alarms produced by motion of the cable, high cable and installation costs, and maintenance of the cable and connectors.
In the above-mentioned copending applications, there is described a continuous wave oscillator-coaxial line resonator-detector circuit and assembly for electromagnetic moving object detection systems. The use of a high Q, coaxial line resonator provides increased sensitivity at reduced power levels, effectively isolates the oscillator circuit from impedance changes in the antenna circuit and reduces interferences from spurious transmissions. Detection of changes in the antenna circuit impedance is performed, in one embodiment, by a crystal rectifier connected to the center conductor of the coaxial line resonator. One of the advantages of this circuit is that the electrical components for signal generation, transmission, reception and detection comprise a single physical entity or unit. If the motion sensing unit is placed at a remote location, ordinary wiring can be used for the power supply and the alarm signal circuits between the remote unit and the central control station.
The protection of large areas against moving intruders normally requires a plurality of remote sensing units each connected to a central control station. It is desirable in large area protection systems to have zone coverage and zone identification of the motion alarm signals. In addition, identification of and discrimination against false alarms should be provided by a system of plural, sequential alarms.
Accordingly, it is a general object of the present invention to provide an alarm system having at least one remote motion sensing unit and a central control station.
It is a specific object of the invention to provide an alarm system having a central control station and at least one remote motion sensor comprising a continuous wave oscillator, a coaxial line resonator, a radiator, and a detector.
It is a feature of the invention that ordinary wiring can be employed for the power supply and alarm signal circuits between the control station and each remote sensor.
It is another feature of the invention that amplification of the detected motion signal can be performed at each remote sensor.
It is another object of the invention to provide a timed, sequential dual alarm. It is a feature of the dual alarm circuit that the circuit is blocked for a predetermined period of time after the first alarm signal and at the end of each full alarm cycle.
It is still another object of the invention to provide an alarm system that will accommodate alarm signals from other condition responsive sensors.
It is a further object of the invention to provide a plural sensor moving object detection system that provides zone coverage and zone alarm identification.
These objects and other objects and features of the present invention will best be understood from a detailed description of a preferred embodiment thereof, selected for purposes of illustration, and shown in the accompanying drawings, in which:
FIG. 1 is a block diagram of the alarm system showing the major components thereof;
FIG. 2 is a schematic diagram of one of the motion sensors;
FIG. 3 is a schematic diagram of the alarm signal amplifier;
FIG. 4 is a schematic diagram of one of the logic circuit gates;
FIG. 5 is a schematic diagram of the sequential, dual alarm timer;
FIG. 6 is a block diagram of one configuration of the logic circuit with a plurality of remote motion sensors; and,
FIG. 7 is a schematic diagram of the line-battery power supply for the alarm system.
Turning now to the drawings, and particularly to FIG. 1 thereof, there is shown in block diagram form an alarm system constructed in accordance with the present invention and indicated generally by the reference numeral 10. The alarm system has at least one electromagnetic moving object detector or sensor 12 comprising a radio frequency oscillator 14, a coaxial line resonator 16, an antenna 18 and a detector 20 for sensing changes in the antenna circuit impedance produced by objects moving within the radiated field pattern in the protected area.
The motion or "alarm" signal is amplified by amplifier 22 and the amplified signal is then fed either to a logic circuit 24 or directly to timer 26. The output signal from the logic circuit is applied to timer 26 or timer 28 in accordance with the logic circuit prewiring. Upon receipt of the alarm signal, timer 26 actuates a first alarm 30 and initiates a timing period of predetermined length. If a second motion or "alarm" signal is produced by motion sensor 12 within the timing period, the timer actuates a second alarm 32. However, if a second alarm signal does not occur within the predetermined period, the timer is reset. An inhibit circuit 34 is provided to block the timer from any alarm signal for a short period after receipt of the first alarm signal and again at the end of the timing cycle. The latter inhibiting of timer 26 eliminates the problem of "ride through" at the end of the timing cycle. Corresponding first and second alarms 36 and 38, respectively, and an inhibit circuit 40 are connected to timer 28.
If more than one remote moving object sensor 12 is used in the alarm system, the output "alarm" signals from the sensors are fed to the logic circuit 24 for processing to one or more of the timers. The additional remote sensors and signal amplifiers are represented as a group 42 by the dashed block in FIG. 1.
The alarm system 10 can accommodate a variety of satellite sensors to provide coverage of other conditions besides the presence of a moving intruder within the protected area. For instance, a heat and/or smoke sensor 44 can be positioned at a critical location with the output from the sensor being directly fed to one of the timers 26 and 28 or alternatively to the logic circuit 24. The latter configuration provides greater interconnection flexibility together with area identification. Additional condition responsive sensors or switches, representationally indicated by block 46 can be wired into the alarm system to share the logic, timer and alarm circuits.
Power for the alarm system 10 is provided by a line operated power supply 48 that has standby DC power capability. Plural stage voltage regulation is used in the power supply and at the RF oscillator 14 to maintain stable operation of the alarm system.
Having briefly discussed the major components of the alarm system, I will now describe in detail the circuitry of the electromagnetic motion sensor 12, amplifier 22, logic circuit 24, timers 26 and 28, and the power supply 48.
ELECTROMAGNETIC MOTION SENSOR
The motion sensor portion of the alarm system is shown in schematic form in FIG. 2. The tunable RF oscillator 14 employs a single, grounded base NPN transistor 50 to generate the continuous, sinusoidal waves that excite a coaxial line resonator 52. A typical operating frequency for oscillator 20 is 400 megahertz. However, other frequencies, generally in the UHF range, can be used for electromagnetic motion detectors. RF ground for the base of transistor 50 is established by a capacitor 54 that shunts base resistor 56. The base resistor 56, together with resistor 58 forms a bias voltage divider from B + regulated to ground. Emitter resistor 60 provides a DC feedback path for oscillator stabilization while RF feedback is prevented by a shunt capacitor 62 which places a RF ground at the bottom of radio frequency choke 64. Coupling of the generated radio frequency energy to the power supply (not shown) is prevented by a second radio frequency choke 66 in the collector circuit.
The required inphase RF feedback to sustain oscillation is provided by the collector-base and emitter-base capacitances. The frequency determining components of the oscillator comprise inductor 68, variable capacitor 70 and a portion of the coaxial line center conductor 72. The oscillator frequency is tuned by varying the series capacitance of the frequency determining circuit. This is accomplished by adjusting the variable capacitor 70.
The oscillator circuit 14 is shielded by an electromagnetic shield shown by the dashed lines in FIG. 2 and identified by the reference numeral 74. Preferably, the oscillator circuit and coaxial line resonator 52 are constructed on a common chassis so that a portion of the oscillator shield 74 is common to the coaxial line resonator outer conductor 76. However, if the oscillator circuit and the coaxial line resonator are physically separated, a current return path must be provided as shown by line 78.
Coaxial line resonators of the type illustrated in FIG. 2 are now generally classified as "cavity" resonators. Henney, Radio Engineering Handbook, 5th Edition, page 6--46. Conceptually, the coaxial line resonator 16 can be regarded as a coaxial transmission line short-circuited at one end and open at the other end. Terman, Electronic and Radio Engineering, 4th Edition, pages 159--161. In the present embodiment, the coaxial line resonator is capacitively loaded and tuned by a variable capacitor 80 located at the open end of the line. This location provides the greatest tuning effect per unit of capacitance. However, other tuning methods, including varying the physical dimensions of the "cavity," can be employed to "peak" the coaxial line resonator.
Physically, the coaxial line resonator or cavity can have a true coaxial construction, i.e., inner and outer cylindrical conductors with a common axis, or a hybrid configuration. One possible hybrid configuration is the so-called "trough line" that has a center conductor positioned within a rectangular prism cavity. The same circuit concepts and tuning techniques are applicable to both the cylindrical and rectangular configurations. However, from the standpoint of mechanical fabrication, production line assembly, and component mounting, the rectilinear configuration is preferable. Construction details of the rectilinear "coaxial line" resonator are illustrated in my above-mentioned copending application for Plural Chambered, Oscillator-Coaxial Line Resonator-Detector Assembly for Moving Object Detection Systems.
The term "coaxial line" has been selected to describe the resonator 52 because it connotes a centrally disposed conductor surrounded by one or more conducting surfaces. This is true even though the conducting surfaces may define a rectangular cavity rather than a cylindrical cavity. Therefore, as used herein, the term "coaxial line resonator" shall mean a resonant cavity having a centrally disposed conductor short-circuited at one end to the conducting surface or surfaces which form the cavity and open at the other end.
The coaxial line resonator 52 has a high Figure of Merit (Q) which allows the oscillator 14 to be very loosely coupled to the resonator. Coupling of the oscillator to the resonator is controlled by the position of the oscillator tap point 82 along the center conductor 72 of the resonator. The coupling should be as loose as possible within the limits imposed by the desired detection range. The loose coupling of the oscillator to the high Q coaxial line resonator circuit effectively isolates the oscillator from motion produced impedance changes in the antenna circuit thereby maintaining the frequency stability of the oscillator.
The coaxial line resonator 52 is constructed with the center conductor 72 having a physical length that is less than one-fourth λ at the operating frequency. The electrical length of the line is adjusted by varying capacitor 80. The output from the coaxial line resonator is capacitively coupled through capacitor 84 to radiator 18. The radiator, which has a length between one-fourth λ and one-half λ, is voltage fed to achieve maximum detection sensitivity. It can be seen from FIG. 2, that the output from the coaxial line resonator is taken at a point 86 which is very close to the point of maximum voltage on the center conductor 72.
Changes in the impedance of the antenna circuit produced by motion of an object within the radiated field pattern of the alarm system are sensed by a rectifier 88. The rectifier is connected to the centerline 72 of the coaxial line resonator at a point 90 located slightly below the output tap 86 for the antenna. The connection point for the rectifier is a compromise between achieving maximum voltage output and minimum effect upon the Q of the coaxial line resonator. A load for the rectifier 88 is provided by resistor 92.
It will be appreciated that in the absence of a moving object, a steady state DC level will be established at the junction of the rectifier 88, load resistor 92 and coupling capacitor 94. When an object moves within the radiated field pattern, the reflected and transmitted energy combine in the antenna circuit to produce a new voltage-current ratio or impedance. Fluctuations in amplitude and phase of the combined signals occur as the object moves through the radiated field pattern. These fluctuations produce an alternating current at the output of the rectifier which rides on the steady state DC voltage. The alternating current or "alarm signal" is coupled through capacitor 94 to amplifier 22.
AMPLIFIER
Referring to FIG. 3, the alarm system employs a high gain, low frequency amplifier 22 to boost the detected motion signal to a level that is sufficient for processing in the logic circuit 24 and subsequent actuation of timers 26 and 28. The amplifier is designed to have a gain of unity at DC and a gain of 2500 at 1.0 hertz with a bandwidth of 0.5 hertz to 3.0 hertz (3 db. points).
The circuitry of amplifier 22 is relatively straight-forward and need not be explained in detail in order to understand the alarm system of the present invention. A high impedance, input stage is provided by a field effect transistor (FET) 96 connected as a source follower to the first stage of a two stage, direct coupled amplifier comprising transistors 98 and 100. The FET input stage allows the use of a much smaller value of capacitance for the coupling capacitor 94. In view of the low frequency bandwidth of the amplifier, this feature is important in terms of the physical size of the coupling capacitor.
Amplification of the detected motion signal is performed by the two stage amplifier circuit of transistors 98 and 100. The bandwidth of the total circuit, i.e., FET 96 and transistors 98 and 100, is determined at the high end by capacitor 102 in the Gate circuit of FET 94 and by a collector-to-base feedback capacitor 104 for transistor 100. The value of the feedback capacitor is selected to provide high frequency clipping over 30.0 hertz and at 35.0 hertz, the gain of the amplifier is unity. The low end of the amplifier bandwidth is controlled by the first stage emitter resistor and capacitor 106 and 108, respectively, and by the corresponding resistor 110 and capacitor 112 in the emitter circuit of the second stage transistor 100.
Two operating controls are provided in amplifier 22: a Linearity control 114 and a Range control 116. Normally, the Linearity control is a factory adjustment that is made to increase or decrease the current flow through the first stage transistor 98 to match the individual characteristics of the input stage field effect transistor 96. The Range control 116 adjusts the gain of amplifier 22 by increasing or decreasing the amount of unbypassed feedback resistance in the emitter circuit of transistor 100. The maximum gain and therefore the maximum range for the motion sensor 12 is obtained when the Range control is set for minimum resistance.
LOGIC GATE
The logic circuit 24 shown in block diagram in FIG. 1 comprises one or more logic gates 118 depicted in schematic diagram in FIG. 4. The output from amplifier 22 is capacitively coupled through capacitor 120 to the base of a normally cutoff transistor 122. The presence of the amplified motion signal at the base of transistor 122, biases the transistor into conduction causing a positive going pulse to be applied to the input of timer 26.
For the present, it is sufficient to note that in a plural sensor system, each remote motion sensor 12 has its own amplifier 22 and logic gate 120 and that two or more of the gates can be prewired with their collectors in parallel to form an OR input circuit for one of the timers. In each case, the prewired parallel gates use a common collector load resistor 124 which is shown in the timer input circuit in FIG. 5.
TIMER
The basic function of the electronic timer 26 is to provide sequential, dual alarm signals to the first and second alarm means 30 and 32, respectively. In order to minimize the possibility of false alarms produced by switching transients and other nonalarm signals, the first alarm control circuitry of the timer is gated for a short period after the first alarm and at the end of each full timing cycle.
The specific circuitry which performs these functions is illustrated in the schematic diagram of FIG. 5. The timer 26 comprises two bistable devices, such as, flip-flops (FF) 126 and 128, two alarm relays 130 and 132 and the associated trigger and gating circuits which will be described below in detail. The energization state of the first alarm relay 130 is controlled by FF 126 while the second alarm relay 132 is energized or deenergized by the action of FF 128. Each flip-flop has two transistors, one normally conducting and the other normally cutoff. For flip-flop 126, transistor 126a is normally conducting and transistor 126b is normally cutoff. Similarly, for flip-flop 128, transistor 128a is normally ON while transistor 128b is normally OFF.
The operation of timer 26 can best be understood by examining the sequence of events produced by the presence of a moving object within the radiated field pattern of the motion sensor 12. The motion of the object through the protected area causes changes in the antenna circuit impedance which generate an AC motion signal at the output of rectifier 88 (FIG. 2). The alternating current motion signal is capacitively coupled to and amplified by the low frequency, high gain amplifier 22. After amplification, the motion signal is capacitively coupled to the base of the normally cutoff logic gate transistor 122. The motion signal forces transistor 122 into conduction causing a positive going pulse to be applied through crystal diode 134 to the base of the normally OFF flip-flop transistor 126b.
Transistor 126b turns ON thereby turning OFF the normally conducting transistor 126a. When transistor 126a stops conducting the first alarm relay 130 deenergizes and actuates the first alarm 30. Various wiring options are available for the first alarm 30 because the first alarm relay 130 has both normally closed and normally open contacts, 130a--130b and 130a--130c, respectively. As shown in FIG. 5, the relay is normally energized and it is assumed that the first alarm 30 is actuated by the closure of the normally open contacts 130a--130c upon deenergization of the relay.
When the normally conducting transistor 126a stops conducting, the power supply voltage appears at the collector of transistor 126a. At this moment, capacitor 136 starts to charge through the path established by resistors 138 and 140 and the coil of relay 130. The RC charge time for capacitor 136 is designed to provide a period of from 3 to 5 seconds before the voltage at the emitter of unijunction transistor (UJT) 142 reaches the firing point of the UJT.
The firing of the UJT trigger 142 applies a positive pulse through isolating crystal diode 144 to the base of the normally cutoff flip-flop transistor 128b causing the transistor to begin conducting. With transistor 128b conducting, transistor 128a is cutoff by the well-known flip-flop action. When transistor 128a stops conducting, the second alarm relay 132 drops out causing relay transfer contact 132a to move from the normally closed contact 132b to the normally open contact 132c.
The second alarm 32 is wired in parallel with the first alarm for closed circuit standby condition and in series for open circuit standby condition. At the very instant that the second alarm relay 132 deenergizes, the conditions for a second alarm are fulfilled. However, this condition is only momentary because of the action of the gating circuit which will be described below. A suitable delay circuit can be inserted in the second alarm circuit to completely eliminate even a momentary second alarm.
When relay 132 deenergizes, relay transfer contact 132d moves from fixed contact 132e to fixed contact 132f. This action puts B + voltage on one side of capacitor 146 causing the capacitor to charge through resistor 148. The positive voltage at the top of resistor 148 biases a normally cutoff field effect transistor (FET) 150 into conduction which in turn causes transistor 152 to conduct.
With transistor 152 conducting, the base of FF transistor 126a is biased almost to the supply voltage because of the relative resistances of resistor 154 and the series circuit of resistances 156 and 158. The resistor 154 has a very low value compared to the series resistance of resistors 156 and 158. For instance, a resistance ratio of approximately 1:50 is suitable to cause hard conduction of FF transistor 126a. This condition will last for one to two seconds while the FET 150 is biased into conduction by the voltage developed by the charging current of capacitor 146. During this period, the first alarm flip-flop 126 is gated against any input signal because even a positive alarm signal would not be sufficient to turn off the hard conducting FF transistor 126a. At the end of the 1--2 second period, FET 150 and transistor 152 stop conducting and FF transistor 126a returns to its normal conducting bias condition.
It should be noted that when FF transistor 126a was triggered into conduction by the FET 150-transistor 152 gating circuit, the first alarm relay 130 was also re-energized. The alarm relay will remain energized until the next alarm signal causes FF transistor 126a to stop conducting.
To recapitulate, at this point in the timer sequence, the first alarm relay is energized and the second alarm relay is deenergized. If another alarm signal is received within a predetermined time period, FF 126 is triggered causing relay 130 to drop out. Since the second alarm relay is already deenergized, the conditions are fulfilled for a second alarm and the second alarm 32 is actuated.
The predetermined time period within which the second alarm signal must occur is established by a trigger circuit comprising unijunction transistor (UJT) 160, capacitor 162 and resistor 164. When the second alarm relay 132 deenergizes, capacitor 162 starts to charge through the path established by resistor 164 and contacts 132d and 132f of the second alarm relay. The RC time constant is selected so that the firing voltage for UJT 160 is reached approximately one minute after the second alarm relay was deenergized. Firing of the UJT trigger 160 puts a positive pulse through isolating crystal diode 166 on the base of FF transistor 128a causing the transistor to start conducting again.
The second alarm relay 132 is again energized and the short circuit across capacitor 168 is removed by the transfer of relay contact 132d from contact 132f to contact 132e. Capacitor 168 functions in the same manner as capacitor 146 by charging through FET gate resistor 148. Both the FET and transistor 142 are turned on causing FF transistor 126a to conduct hard for another 1--2 second period. The gating of the first alarm flip-flop at the end of each full timing cycle is done to prevent any possibility of timer "ride through" caused by switching transients.
A conventional tamper switch 170 is provided for the alarm system to give a warning of any physical disturbance to the system. Opening of the normally closed tamper switch 170 breaks the emitter circuit for FF transistor 126a causing relay 130 to drop out which in turn actuates the first alarm 30.
A key switch 172 is also provided in the alarm system to prevent alarms during normal business hours or at any other time selected by the user. The key switch 172 is normally closed in the ALARM condition. When the switch is opened for STANDBY operation, resistor 174 is added to the gate circuit of FET 150 and, together with resistor 176, forms a voltage divider from B + to ground. FET 150 is biased ON by the voltage divider and remains conducting as long as the key switch is open. Since FET 150 is conducting, transistor 152 will also be conducting with the result that FF transistor 126a will conduct hard until the key switch is closed. In this condition, it is impossible to turn OFF FF transistor 126a with any alarm signal that is applied to the base of FF transistor 126b.
LOGIC CIRCUIT
In an alarm system having a plurality of remote motion sensors 12, and a corresponding plurality of amplifiers 22, a variety of interconnection configurations can be employed to provide the desired degree of zone coverage and zone identification of alarm signals. Given an eight sensor system, the interconnection arrangements can vary from eight sensors driving eight amplifiers and eight gates 118 that are logical OR connected, or at the opposite pole, each sensor-amplifier can have its own separate timer. It will be appreciated that the alarm system of the present invention is not limited to any specific interconnection configuration and that in the simplest form, the system can comprise a single motion sensor driving an amplifier which in turn is connected to a single, sequential dual alarm timer that actuates the first and second alarms.
One representative example of an eight sensor interconnection arrangement is illustrated in block diagram in FIG. 6. Of the eight motion sensors, four sensors 12a through 12d are connected through their corresponding amplifiers 22 and gates 118 to a single timer 26 a--d so that a motion signal from any one of the four sensors will actuate the timer. The logical OR function is performed by prewiring the output collector circuits of the gates in parallel to a common load resistor, such as, resistor 124 shown in the timer diagram of FIG. 5. Two of the remaining sensors, 12e and 12f, are prewired in an OR configuration to another timer 26e--f. The last two sensors, 12g and 12h each have their own individual timers, 26g and 26h, respectively.
Other configurations can be employed to meet the particular characteristics of the protection environment. It has been found that a Four-Two-Two sensor configuration with three timers is practical and has a good degree of flexibility.
The separate sensor-timer arrangements are useful when specific zone coverage and zone identification are required. For instance, the four OR wired motion sensors 12a through 12d could be used for perimeter zone protection while the single separate sensors could be used in one or more areas requiring maximum security.
POWER SUPPLY
The basic line-battery operated power supply 48 has two stages of voltage regulation as shown in FIG. 7. A third stage of voltage regulations is provided for the RF oscillator 14 to compensate for voltage drops in the wiring between the central station power supply and the remotely located motion sensor oscillator. The circuitry for the third stage regulator is shown in the amplifier schematic of FIG. 3 and will be discussed later on.
Referring now to FIG. 7, the power supply 48 comprises: a standby, rechargable battery 178; a line operated, full wave rectifier 180; a first stage series voltage regulator 182; a battery charger and control circuit 184; a second stage series voltage regulator 186; and, a zener referenced, four stage DC amplifier control circuit 188 for the second stage regulator 186.
In normal operation, the alarm system circuits are powered by the rectified line current. Battery 178 is provided for standby DC power in the event of power line failures. The battery is maintained in a charged condition by battery charger 184 that utilizes a control transistor 190 to vary the base current of the series regulator 182. A voltage reference for the control transistor 190 is established by a single field effect transistor (FET) 192. Another field effect transistor 194, connected as a source follower, is interposed between the voltage reference transistor 192 and the control transistor 190 to act as a buffer.
Short circuit protection for battery 178 is provided by a circuit breaker 196. Protection for the line operated supply is obtained by cutting off both the series regulator 182 and the control transistor 190 whenever the current drain exceeds a predetermined amount. The series regulator 182 is cutoff by diode 198 when the voltage drops across resistor 200 and the base-emitter junction of regulator 182 exceeds the forward voltage required to overcome the junction potential barrier of the diode. A similar action occurs in the control transistor 190 with respect to resistor 199 and the series diodes 201.
The second stage, series voltage regulator 186 is controlled by the four stage DC amplifier 188 that is referenced to Zener diode 202. If the motion sensor RF oscillators were located at the central station two stages of power supply regulation would normally be sufficient. However, the oscillators are usually located at a distance of up to 300 feet from the central station. At such distances the voltage drops in the connecting wire must be compensated for by an additional stage of voltage regulation at the oscillator itself.
In the preferred embodiment of the invention, the amplifier and RF oscillator are housed in the same unit so that load length between the amplifier assembly and the oscillator can be considered negligible from the standpoint of a voltage drop. Looking at the amplifier assembly schematic shown in FIG. 3, it can be seen that the output from the second stage power supply regulator is applied to a third stage regulator, indicated generally by the reference numeral 204. The third stage regulator comprises a series transistor regulator 206 and a central transistor 208 that is referenced to Zener diode 210. The regulated output from transistor 206 is used to power both the RF oscillator 14 and the amplifier 22.
Having described in detail the preferred embodiments of the alarm system, it will now be apparent to those in the art that numerous modifications can be made thereto without departing from the scope of the present invention.