US 3754214 A
An electronic security system provides for the remote encoding of a lock utilizing at least two adaptive memory devices, one of which corresponds to the lock and the other to the key, the devices being each placed in a predetermined state to provide an output signal therefrom having a given level corresponding to the state of that device in response to an applied input signal. Only when the devices are in matched states will the security system provide a desired security control signal.
Description (OCR text may contain errors)
United Stat Matsumoto et a1 ELECTRONIC SECURITY SYSTEM  Inventors: Yasushi Matsumoto, Narashino;
Yoshiaki Kuwahara, Tokyo, both of Japan  Assignee: RCA Corporation, New York, NY.
 Filed: Dec. 30, 1971 ] Appl. No.: 214,272
 US. Cl. 340/149 R, 317/134  Int. Cl. Gllb 9/02  Field of Search 340/147 R, 149 R,
H1961 Loewe .134O/149 R X 3/1979 Benford 340/164 R X Primary Examiner-Donald J. Yusko Att0rney-Edward J. Norton  ABSTRACT An electronic security system provides for the remote encoding of a lock utilizing at least two adaptive memory devices, one of which corresponds to the lock and the other to the key, the devices being each placed in a predetermined state to provide an output signal therefrom having a given level corresponding to the state of that device in response to an applied input signal. Only when the devices are in matched states will  References Cited UNITED STATES PATENTS gliigemsltlecunty system provide a desired securlty control 3,641,498 2/1972 Hedin 340/164 R 3,453,598 7/1969 Schweizer 340/149 A 21 Claims, 9 Drawing Figures h IT l 24 l H I I6 I I I6 I 26 OSCILLA\TOR ADAPTIVE 3 I I 3 ADAPT 1 IVE 28 I I MEMORY MEMORY 30 DEVICE |8 I DE AM)P i L 2 m i p 20 2 Y COMPARATOR l 7 .a, V.. o J KEY 2Q SECURITY CONTROL 32 SIGNAL GENERATOR ELECTRO- 22 PULSE MECHANICAL CHARGING LATCH UNIT e PATENTEOAUBN I973 SHEET 1 OF 2 OSCILLATOR ELECTRO- MECHANICAL LATCH ADAPTIVE MEMORY l} 20 ECURITY CONTROL SIGNAL GENERATOR KEY PULSE UNIT CHARGING ELECTRONIC SECURITY SYSTEM This invention relates to electronic security systems and more particularly to electonically encoded lock and key arrangements.
Generally, the purpose of a security system is to permit access to a given secured area by only authorized or selected people, preventing access to these areas by all others. The secured areas may include hotel rooms, automobiles, locks, filing cabinets, cabinets in general, homes, offices, buildings and the like. Many different systems have evolved over the years to provide a certain measure of security to the given areas. However, all these systems have certain disadvantages. For example, in a mechanical system utilizing a common lock and key arrangement wherein a mechanical key is closely fitted to a corresponding lock, the physical shape of the key is encoded to the physical shape of the lock mechanism so that only a given key can be utilized with a given lock. It becomes necessary with such a system to replace the lock and its associated key when the security system is broken; that is, when an unauthorized person comes into possession of a key or the mechanical code by which the lock is constructed. This can be costly and expensive, especially in such applications as in hotels. Other systems which include electromechanical devices and which use electronic coding have the disadvantage of using discrete irreplacable codes for both the lock and so called key arrangement. In this latter system the so called key has discrete components therein which provide a signal comprising a number of different encoded frequencies. However, like the mechanical key, this electronic key is also permanently configured so that once it is constructed to include a given electronic code, the security system comprising the lock and key must necessarily also be replaced or otherwise worked upon to change the coding arrangement which may prove burdensome in many applications.
Thus, either the purely mechanical lock and key arrangement or the purely electronic or even combinations thereof in the prior art, all entail utilization of a permanently encoded key and lock system. which, if either the coding arrangement, or the key mechanism itself, falls into the hands of an unauthorized person, then the security system is broken and needs to be replaced. Such action is drastic for most applications and can be complex and costly as well.
SUMMARY OF THE INVENTION In accordance with the present invention, an electronic security system is provided in which key means include a first adaptive memory device capable of assuming a plurality of states, the device providing in response to an applied input signal an output signal having a plurality of levels, each level corresponding to a respective separate different state. Security control means are provided for receiving the key means and include a second like adaptive memory device. Comparison means are coupled to the memory devices for comparing the output signal levels thereof in response to an input signal applied thereto and for providing a security control signal only when the key and security control means are engaged and the devices are in matched states.
It is a feature of the present invention to provide means for remotely encoding the memory device in the security control means so that the security codes can be changed remotely. Thus, by electronically changing the state of the memory device in the security control means and in the corresponding key, the system code is changed efficiently and quickly.
IN THE DRAWINGS FIG. 1 diagrammatically illustrates an electronic security system in accordance with the present invention;
FIG. 2 illustrates an isometric view of an adaptive memory device utilized in an embodiment of FIG. 1;
FIG. 3 is a schematic illustration of the circuit of the device of FIG. 2;
FIG. 4 is a schematic drawing of a pulse charging unit for use in the embodiment of FIG. 1;
FIG. 5 is a second embodiment diagrammatically i1- lustrating an electronic security system in accordance with the present invention having three stages;
FIGS. 6a, 6b, 6c and 6d diagrammatically illustrate a key and mating lock receptacle incorporating three adaptive memory device stages.
DESCRIPTION OF THE INVENTION In FIG. 1, there is schematically illustrated an electronic security system comprising key 10, security control signal generator 12, and electro-mechanical latch device 14. The key and signal generator each have respective mating contact terminals l6, l8, and 20 and I6, 18' and 20'. The output of the security control generator is applied along lead 22 to latch 14.
Both key 10 and signal generator 12 include adaptive memory devices 24 and 26, respectively, to be described. Oscillator 28 provides an input alternating sine wave signal at input terminals 1 and I of devices 24 and 26, respectively. Common terminals 3 and 3 of devices 24 and 26 are coupled to ground or a suitable reference potential as shown. output terminals 2 and 2 of respective devices 24 and 26 are each coupled to a separate input terminal of a comparator 30. The output of comparator 30 is applied through amplifier 32 to lead 22 for applying the comparator output signal to electromechanical latch 14.
Pulse charging unit 34 is coupled to terminals 2 and 2' of devices 24 and 26, respectively. Unit 34 applies an input signal at terminals 2 and 2' to each of the adaptive memory devices to change the state of the de vices in a manner to be described. The output signal of the devices at terminals 2 and 2' thereof will be at a given level in accordance with the state of these devices as set by the applied signal by unit 34 when oscillator 28 applies a given input signal at terminals 1 and I to each of the adaptive memory devices 24 and 26, respectively.
In accordance with the present invention, adaptive memory device 24 is disposed in a key 10 or other suitable removable connecting device adapted for convenient carrying on an individual. Security control signal generator I2 is coupled to a suitable receptacle to be described having terminals I6, 18 and 20' which mate with terminals I6, 18 and 20 of the key when the key is inserted in that receptacle.
Prior to discussing the operation of the security system in accordance with the present invention, a brief description will now be given of the adaptive memory devices 24 and 26. Generally, an adaptive electronic device is a circuit element whose transfer characteristic can be adjusted or set by an adapt or control signal and which will retain that characteristic after the signal has been removed. The term transfer characteristic means that, in response to a given input signal applied to the device, the device will provide an output signal of a given level. That is, the output level of the device may be varied in level by adjusting the state of the device, so that when the input signal is applied thereto, the output signal, in accordance with the transfer characteristic of the device, will have a predetermined signal level which corresponds to that set state. The adaptive electronic device has transfer characteristics which are reversably adjusted or adapted to these various states between two extreme limits by the application of a specific pulse of electrical power. Thus the adaptive device is essentially an analog memory element.
In all cases, the state of the transfer characteristics of the device remains substantially stable with respect to time and ambient conditions. Other properties of the transfer characteristics include broad range of adjustment, ability to switch state rapidly, reproducibility of the stored state, low switching energy requirements and ability to maintain the stored state in the absence of applied power.
The adaptive memory device, in accordance with the present invention, is preferably an adaptive ferroelectric transformer.
In FIG. 2, there is illustrated an embodiment of an adaptive ferroelectric transformer 36 which is included in the embodiment of FIG. 1 as adaptive memory devices 24 and 26, respectively. The adaptive transformer comprises a pair of mechanically coupled ceramic lead zirconate/lead titanate capacitors 38 and 40. Capacitors 38 and 40 each comprise a ferroelectric material 42 and 44, respectively, sandwiched between respective outer matallic plates 46 and 48 and a common intermediate metallic plate 50 or center vane connector. Electrically coupled to plates 46, 48 and 50 are conductive contact terminals 1, 2 and 3, respectively.
Both the ferroelectic and piezoelectric properties of the capacitor material are utilized in the operation of the adaptive transformer. Microscopic domains in ferroelectric material lie in one of two stable states of polarization. Most of the domains can be polarized in the same direction by applying a sufficiently high electric field across the material. A characteristic of each of the domains capable of being polarized in the ferroelectric material is that polarization can be partial or total depending upon the electric field across the material. The degree of the polarization depends upon the crystal structure of the ferroelectric material; that is, singlecrystal materials pole more effectively than ceramic materials. The direction of the polarization can be reversed by reversing the polarity of the applied field. If, however, the reversed field is applied as a short pulse, some of the domains will reverse while others will not, in which case, the material is said to be in a state of partial polarization. The magnitudes and polarities of the piezoelectric effects in the material are directly related to the states of partial polarization. Since the polarization states and corresponding piezoelectrical coefficients are stable in ferroelectric materials, such as lead zirconate/lead titanate compositions, they can be used to provide analog memory in devices such as the adaptive ferroelectric transformer described herein.
In FIG. 3, an electrical equivalent circuit representing the device of FIG. 2 as a two-port network is shown. Each of capacitors 38 and 40 are coupled to their re' spective terminals 1 and 2 and to a common terminal 3. These capacitors have a small dissipation factor, depending on the ferroelectric material employed which has not been included in the equivalent circuit representation. Conventional magnetic dot notation is used to indicate signal phase information while an arrow notation (arrowhead positive) indicates the polarity of the polarization state of the transformer capacitors.
Input capacitor 38 transforms electrical energy into mechanical energy and output capacitor 40 performs the opposite transformation. The capacitors are coupled by mechanical connector 50. By combining each of the capacitors 38 and 40 as shown into one effective transformer, there are three capacitances provided, c c and c which are the respective capacitances of capacitors 38, 40, and the mutual capacitance coupling the input and output circuits of the transformer 36. An a.c. input signal applied to the transformer at capacitor 38 induces an a.c. output signal response at capacitor 40. The magnitude of the output signal is determined by the value of the mutual capacitance C,,,, which is a function of the states of polarization of both the input and output capacitors of the transformer.
In operation of the adaptive ferroelectric transformer, an a.c. signal is applied to the input capacitor 38. The signal is transformed by the inverse piezoelectric effect into an acoustic signal which is coupled into the output capacitor 40, where due to the direct piezoelectric effect, it is transferred into an electric signal similar in wave shape to that of the input signal. If the materials of both capacitors are fully polarized to obtain maximum piezoelectric effects and the frequency of the input signal is within the flat band region of the transformer characteristic, the output signal will be set to its maximum value (maximum voltage gain) and will have a phase shift of 0 to The polarization of either capacitor can be changed in steps of any desired magnitude by applying specific voltage control pulses. As a result, the effective piezoelectric coefficient (d) can be set at any desired value in a range which represents the saturation values corresponding to the maximum positive and negative saturation polarization states. This way, it is possible to set the voltage gain of the transformer anywhere within a given range because the voltage gain is directly related to the magnitudes of the effective piezoelectric coefficients (d). The switching time of the device which is determined by the amplitude of the control pulse can be at least as fast as 1 0" seconds. The magnitude of the a.c. input signal can be large but has to be held below that required to alter the state of polarization of the input capacitor.
To provide a flat voltage gain characteristic in a given frequency range, it has been found that the device of FIG. 2 should be potted, (not shown). Rigid potting material such as high temperature waxes, epoxies, plastics and casting compounds store the least amount of energy and yield the highest gain in values. Elastic or rubbery materials generally yield very low values of gain. The geometry of the transformer structure has little influence on the magnitude of the gain provided the width W and length L are each equal to or less than ten times the total thickness T of the device.
Adaption of the gain characteristic of the transformer is accomplished by changing the state of polarization in either the input or output capacitor. A large positive or negative voltage applied to the capacitor sets d or d the piezoelectric coefficients of capacitors 38 or 40, respectively, whose positive or negative saturation value is (1,. Negative or positive voltage pulses of shorter duration or lowered amplitude cause d or d to change from +d, or -d,, to a lower magnitude and then eventually come to a negative or positive saturation value. An arbitrary value of d, or d within this range can be obtained or set by a control pulse or a sequence of control pulses of a specific amplitude and time duration.
The gain of the adapted ferroelectric transformer can be set by the application of a sequence of control pulses or a single control pulse of longer duration. The higher the pulse amplitude and the longer the pulse duration, the fewer will be the number of pulses required to set the gain to a specific value. Additionally, after a gain magnitude has been established by control pulse, it can be increased further or decreased back toward the reset value by the application of more control pulses of the same or opposite polarity, respectively. In general, a sequence of short control pulses yields a polarization state close to that obtained by one long pulse of corresponding length and equal amplitude. An adaptive fer roelectric transformer and similar devices are further described in an article entitled An adaptive Ferroelectric Transformer-A Solid-State Analog Memory Device" by J.H. McKusker and S. S. Perlman in the IEEE Transactions on Electron Devices, July 1970, pp. 534 to 540 and in an article entitled An Adaptive Resonant Filter" by Stuart S. Perlman and Joseph H. McKusker in Proceedings of the IEEE, Vol. 58, No. 2, Feb., 1970, pp. 190 through 197.
To adapt or set the polarization state of the adaptive ferroelectric transformer device, a pulse charging unit 34 of FIG. 4 shows schematically may be utilized.
In FIG. 4, a variable d.c. power supply 52 is coupled by way of a double throw, double pole switch 54 to terminals 2 and 3 and 2 and 3' of adaptive memory devices 24 and 26, respectively. The polarity of the transfer characteristics of each of the memory devices can be changed by a particular switch position of switch 54. Suitable control means 53 coupled to both the power supply 52 and switch 54 control the amplitude of the output signal of supply 52 and the duration that switch 54 is in the closed position to thereby control both the pulse amplitude and duration applied to the memory devices 24 and 26.
By applying a control pulse from power supply 52 to devices 24 and 26 of a given amplitude and for a given time duration, the polarization state of each of devices 24 and 26 are, in accordance with the present invention, placed in matched states. Matched pairs are provided with a predetermined degree of polarization as described above so that only the matched pairs provide the desired output from comparator 30.
By the term matched state is meant that the degree and polarity of the polarization state of the adaptive device in a key as compared to its corresponding adaptive device in the security control signal generator are such that when the output signals of the device are compared, the output of the comparator comparing the signals provides the desired security control signal only when the adaptive devices are in a predetermined given polarization state. This predetermined state could be identical in the devices or different, providing that the difference of the output signals provided in response to the applied a.c. input signal when these devices are each in the predetermined states is detected by suitable means.
in operation of the system of FIG. 1, the adaptive device 24 in key 10 is disposed in a suitable connecting arrangement which is connected to the security control signal generator 12. As shown, oscillator 28 provides an input signal of a suitable frequency within the flat bandwidth range of each of the adaptive devices at respective terminals 1 and 1'. When the adaptive device of the key matches the adaptive device of the security control signal generator, then the output signal at the terminals 2 and 2' thereof will be at the predetermined levels whether the same or different in accordance with the particular configuration. That is, the transfer characteristics of a key and its mating control signal generator 12 match so that when the input signals are applied thereto, the output signals when compared by comparator 30, will provide the security control signal at lead 22 through amplifier 32. The security control signal will then cause, the electro-mechanical means, the operrtion of a security device such as a latch in a lock or other suitable locking devices. Only when a key 10, having the properly matched device 24, is coupled to its mating security control signal generator 12 will an output signal be provided at lead 22 to operate latch 14.
Advantageously, the encoding of this security system can be accomplished remotely from the physical location of both the key receptacle and latching mechanism. This remote encoding is achieved by pulse charging unit 34. Pulse chargingunit 34 may be permanently hooked up electrically into the security control signal generator circuit or may be insertable' by suitable plug and jack configurations. in the latter case, the operator as provided-by the present invention, merely couples the pulse charging unit 34 to the adaptive memory device 26 in he security control signal generator. The devices then change in transfer characteristic thus changing the level of the output signal upon application of the oscillating signal from oscillator 28. At the same time, the associated key has its adaptive memory de vice changed by pulse charging unit 34 in a suitable receptacle, not shown, remote from the receptacle of the security signal control generator and provided especially for coupling to the pulse charging unit 34. Thus not only can a latching mechanism, in accordance with the present invention be operated upon remotely by authorized persons, but should the key fall into the hands of an unauthorized person, ,a new key and a new lockingcode can be immediately provided the system upon loss of; presently available key: Thus locks for hotel rooms, airline terminal lockers, industrial plant entrances and exists can have their locking codes immediately changed upon loss of security of the code.
In accordance with the present invention, many different combinations and permutations of lock and key codes are provided. Not only may a key be mechanically encoded as presently accomplished, but the key may also be provided with a large plurality of electronic codes. These codes can be provided in accordance with the number of different levels of adaptive memory device output signals that can be detected by the present state of the art detecting devices. Additionally, the code can be further enhanced by providing a plurality of adaptive devices in each of the key and mating security control signal generator.
This latter system is illustrated in FIG. in which there are three adaptive device stages, each having a pair of devices and the corresponding comparator. As shown in FIG. 5, three adaptive devices 54, 56 and 58 are shown in key 60, each of the devices corresponding to respective adaptive device 54', 56' and 58' in security control signal generator 62. The output of each comparator 54", 56" and 58" corresponds to the respective matched pairs of adaptive devices as shown. When the outputs of all the comparators match, a security control signal is provided at lead 64 through amplifier 66. Not only may the devices be encoded in accordance with the transfer characteristics thereof, but a code including a plurality of sets of devices further provides an increase in the number of different possible codes. While three stages are shown, each having its own pair of adaptive devices and comparator, in practice, many more than three may be utilized.
A suitable type of latching mechanism is schematically shown in FIG. 5 having an electro-mechanical transducer 68 whose plunger 70 retains latch tongue 72 in the locked position in an aperture in door 74, the latch and plunger being located in door 76 or other suitable access covering to a secured area. Latch 72 is spring biased in its lock position in a suitable manner so that upon the key matching with its corresponding security control signal generator the security control signal will be applied at lead 64 causing plunger 70 to release latch tongue 72 so that a suitable knob 78 may operate the tongue 72 releasing it from wall 74.
In FIGS. 6a through 6d, there is shown an illustrative example of a suitable key and mating receptacle as provided in accordance with the present invention. Hollow key 80 encloses three adaptive devices 82, 84 and 86, which are wired as shown to external contact terminals 88. Key 80 is mechanically encoded by a suitable recessed slot 30. A mating receptacle is shown in FIGS. 60 and 6d, the receptacle of FIG. 6d being an end view along line 6-6 of FIG. 60. Receptacle 92 is provided with a slotted aperture 94 and a like plurality of spring loaded contact members 96, each of which separately engage a different one of contact terminals 88 on key 80. Aperture 94 has a suitable ridge 98 which corresponds to recess 90. While a conventional key configuration has been illustrated, it is to be understood that in practice, any electrical interconnecting configuration may be utilized for interconnecting the key 80 to a suitable receptacle.
Thus, there has been shown, in accordance with the present invention, an electronic security system utilizing adaptive memory devices, each of which is capable of assuming a plurality of different states, to provide a different predetermined output signal level in response to a given input signal. When the devices of the key and the mating security control generator match, then a security control signal is generated and a security device is operated thereupon. The adaptive devices are capable of remote encoding, permitting rapid and frequent changes of a particular system code while maintaining the integrity of the security of the system. By utilizing adaptive memory devices, in accordance with the present invention, with conventional mechanical keys, the locking systems of such conventional systems are even further enhanced.
What is claimed is:
1. In an electronic security system, the combination comprising:
key means including a first adaptive ferroelectric transformer capable of assuming a plurality of states, said transformer providing an output signal in response to an applied input signal, said output signal having a certain level corresponding to a given state, and security control means for receiving said key means including a second adaptive ferroelectric transformer and comparison means coupled to said second transformer for comparing the output signal level of said first and second transformers to provide a security control signal only when said key and security control means are engaged and said transformers are in matched states. 2. The system of claim 1 further including pulse generating means coupled to said security control means for changing the state of said second transformer.
3. The system of claim 2 wherein said pulse generating means is disposed remote from said security control means.
4. The system of claim 1 further including means coupled to said security control means for applying said input signal to said transformers when said key means are engaged.
5. The system of claim 4 wherein said input signal means is an oscillator.
6. The system of claim 5 wherein said security control means includes releasable latch means having lock and unlock positions and means responsive to said security control signal coupled to said latch means for placing said latch means in either the locked or unlocked state.
7. In an electronic security system, the combination comprising:
key means including a first memory device capable of assuming a plurality of states, said device providing an output signal in response to an applied input signal, said output signal having a parameter having a certain value corresponding to a given state, and
security control means for receiving said key means including a second like memory device and comparison means coupled to said devices for comparing the output signal parameter values of said first and second devices in response to an input signal applied thereto and for providing a security control signal only when said key and security control means are engaged and said devices are in matched states.
8. An electronic security system, comprising:
means including a first adaptive memory device capable of assuming a plurality of states said device providing an output signal in response to an applied input signal, said output signal having a certain level corresponding to a given state, security control means for receiving said first mentioned means including a second like adaptive memory device and comparison means coupled to said second device for comparing the output signal level of said first and second devices and for providing a security control signal when said first mentioned means and security control means are engaged and said devices are in predetermined states,
means coupled to said security control means and said first mentioned means for setting said predetermined states,
means responsive to said security control signal applied as an input thereto including a security device having secured and unsecured states for placing said security device in either of said states, and
means coupled to said security control means for applying said first mentioned input signal to said memory devices when said first mentioned means and said security control means are engaged.
9. An electronic lock system capable of remote encoding, comprising:
connector means including a first device capable of assuming a plurality of states in response to an electrical signal applied thereto, said device providing an output signal in response to an applied input signal, said output signal having a certain level corresponding to a given state,
receptacle means for receiving said connector means means coupled to said receptacle means including a second device capable of assuming a plurality of states in response to an electrical signal applied thereto, said second device providing an output signal in response to an input signal, said output signal having a certain level corresponding to a given state and further including comparison means coupled to said second device and to said first device for comparing the output signal levels of said first and second devices to provide a lock control signal when said engaged devices are in predetermined states,
means disposed remote from said receptacle means for setting said predetermined state of said first and second devices and for remotely encoding said second device to match said first device, and
means coupled to said second device for applying said input signal to said devices when said connector and receptacle means are engaged.
10. A key member for use in an electronic security system of a type including an adaptive electronic memory device capable of assuming and retaining any one of a plurality of electronic states, said system further including means for generating an output signal from said device corresponding to the state thereof and for providing a security control signal upon a given match existing between said output signal and an input signal, said device and said means being connected to a first plurality of terminals, said key member comprising:
a second adaptive electronic memory device capable of assuming and retaining any one of a plurality of electronic states,
a second plurality of terminals adapted to contact with said first plurality of terminals,
means for coupling said second plurality of terminals to said second device such that said generating means can operate said second device via certain of said first and second plurality of terminals when in contact to cause said second device to generate said input signal according to the then state of said second device, said input signal being provided to said generating means via other of said first and second plurality of terminals when in contact,
said security control signal being provided only when said first and second plurality of terminals are in contact and the states of said first and second devices are such as to provide said given match between said output and input signals.
11. A key member as claimed in claim wherein said first and second devices are ferroelectric transformers.
12. In combination:
an analog memory device providing an output signal in response to an applied input signal having a certain ratio therebetween anywhere within a first given range determined by the selected value anywhere within a second given range of a device control signal previously applied to said memory device,
a plurality of terminals, means coupling said terminals to said device such that an input signal applied to said device via at least one of said terminals results in an output signal at at least one other of said terminals having a value corresponding to the then state of said device, and means housing said device, said terminals and said coupling means to provide a transportable key-like member for use in an electronic security system.
13. The combination 12 as claimed in claim 12 wherein said member is formed to operate in a standard groove and ridge mechanical lock.
14. The combination as claimed in claim 12 wherein said device is a ferroelectric transformer.
15. The combination, comprising:
a first adaptive ferroelectric transformer charged to provide a first output signal of predetermined level in response to an input signal applied thereto,
a second adaptive ferroelectric transformer charged to provide a second output signal of a predetermined level in response to an input signal applied thereto,
a signal comparator coupled to said first transformer,
means for coupling said second transformer to said first transformer and said comparator to cause said comparator to compare the levels of said output signals applied as inputs to said comparator to provide a control signal when said levels are matched, and
latch means having lock and unlock states coupled to said comparator and responsive to said control signal, said latch means being switched from one of said lock and unlock states to the other when said control is applied thereto.
16. in an electronic security system, the combination comprising:
an analog memory device providing an output signal in response to an applied input signal having a certain ratio therebetween anywhere within a first given range determined by the selected value anywhere within a second given range of a device control signal previously applied to said memory device, and
a signal comparator coupled to said device for comparing the value of said output signal to the value of a first signal applied as an input thereto and provide a security control signal when said values are matched.
17. The combination of claim 16 wherein said selected value is determined by the amplitude and time duration of a pulse.
18. The combination of claim 16 including control signal generating means coupled to said device for applying said device control signal to said device.
19. The combination of claim 16 further including latch means having lock and unlock states coupled to said signal comparator and responsive to said security control signal, said latch means being-switched from one of said lock and unlock states to the other by said security control signal.
21. The combination of claim 16 further including a plurality of like memory devices and a like plurality of signal comparators each being coupled to a separate, different respective one of said devices, and encoded signal generating means responsive to the output signals of said comparators applied as an input thereto for generating said security control signal when said comparator output signals match a given code.
Patent No, 3,754,214 Dated August 21, 1 973 Inventor) Yasushi Matsumoto and Yoshiaki Kuwahara It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Title Page, add:  Foreign Application Priority Data October 27, 1971 Great Britain 49,930/71;
Col. 5, line 34, "shows" should be shown Col, 6, line '21, Correct "operration" to read operation Col. 6, line '51, After "of" insert the Col. 7, line 57, Correct "30" to read 90 Col, 10, line 41, After "contro1" insert signal Col. 10, line 53, After "thereto" change "and" to read Signed and sealed this 18th day of December 1973.
EDWARD M. FLETCHER, JR RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM PC4050 (10-59)