US2912683A - Apparatus for photoelectric intruder detection - Google Patents

Description

S. M. BAGNO Nov. 10, 1959 APPARATUS FOR PHOTOELECTRIC INTRUDER DETECTION Filed Dec.

2 Sheets-Sheet l AGENT S M. BAGNO Nov. l0, 1959 2 Sheets-Sheet 2 HIH INVENTOR Samuel M, Bagno AENT vBY Y ters.

United States Patent O APPARATUS FOR PHOTOELECTRIC INTRUDER DETECTION Samuel M. Bagno, Belleville, NJ., assignor to Walter Kidde & Company, Inc., Belleville, NJ., a corporation of New York VApplication December 31, 1956, Serial No. 631,544

8 Claims. (Cl. 340-258) vThe present invention relates to a photoelectric intruder detecting system, and,l more particularly, to such a system employing light waves of modulated intensity.

The use of tamperproof photoelectric systems employing fail-safe means is a common practice in burglarproofing areas by continuously monitoring their perime- Such systems commonly employ a low intensity or modulated light source to provide the tamperproof function, and Aa D.C. power source is incorporated to provide for safety in the event of power failure.

In order to provide a system which may be operated froma conventional alternating current power source,

or, equally well, from a direct current standby source, it has been found expedient to employ a lamp such as a neon bulb which is characterized by its distinctly different discharge and quench voltage values. Such a lamp may be oscillated by a capacitor continuously charging and discharging across the electrodes of the lamp. For example, U.S. Patent No. 2,631,273 discloses a system employing a neon lamp and a conventional photocell receiver. I

Such a system has several inherent drawbacks which seriously affect reliability, practicality and cost. The use of a neon lamp, for example, is expensive and places a definite limitation on the maximum permissible physical range covered, neon lamps not being an intense source of light. Further, the question of useful life enters into the consideration which also is a limitation. The use of conventional photocells presents another drawback in that they are either unstable or unsuited because of their high impedance to drive transistor circuits, transistor circuits being necessary because of their low power requirements.

Accordingly, the primary object of the present invention is to provide a foolproof photoelectric intruder detecting system having superior reliability to such systems heretofore known. v

Another object is to provide such a system which employs components that come closest to having infinitely long life and to use lthem at a level wellbelow their rated electrical capacity. Y

Another object is toprovide such a system which is easily manufactured and requires arminimugm of maintenance. l

Another object is to provide such a system which requires a minimum ofpower in' the course of normal opeation.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon ememployment of the invention in practice.

IIn, accordance with the present invention, it has been found that the foregoing objects can be accomplished by providing a system generally comprising a constant amplitude direct current source, such as either rectified and filtered Yalternating current or standby battery; a self- "ice sustaining, tuned oscillator; an incandescent electric lamp powered by the oscillator; a light sensitive junction type transistor so positioned to receive modulated light beams passing across the area to be protected; an amplifier for the output of the transistor; phase correction means for the amplifier output; and phase sensitive means controlled by the phase correction means. The phase sensitive detector means has its input connected to the oscillator and its output connected to that type of an alarm system which has a normally energized alarm control relay. s

A preferred embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein: .Y

Fig. 1 is a block diagram showing the essential components in accordance with the invention.

Fig. 2 is a schematic wiring diagram of the system shown in Fig. l.

Referring to Fig. l, there is shown an alternatin current power source 10 which in its most convenient form transforms 110 volt 60 cycle service power to a regulated, low voltage alternating current, and arectifier filter network 11 which converts the regulated output of the alternating current source to direct current having a substantially constant direct current voltage level. The output of the rectifier-filter is operatively connected with the output of a battery standby 12 having an equivalent voltage for supplying current to an oscillatorV 14.

The oscillator provides an output of regulated alternating current, regardless of which power source is used, for powering and modulating an incandescent lamp 15 in a manner to produce a reference signal adapted to actuate an alarm control as will be described hereinafter.

The light source 15 is so positioned in a space to project light waves across the area to bemonitored, and a photosensitive device 16 is so located to receive these waves when normally unobstructed and produce a signal. The output signal of the photosensitive device is then fed into au amplifier 17 which in turn feeds the amplied signal to a phase correction network 19. The purpose of the phase correction network is to restore the phase of the signal to that of the oscillator 14 output. As will be easily understood, the heating of an electric light filament to incandescence lags the current applied by a significant amount. Therefore, in order to maintain the light signal and the reference signal in exact phase, it is necessary to correct the former.

A phase sensitive detector 20 is controlled by the output of the phase correction network 19 to allow the reference signal from the oscillator 14 to pass and to ultimately maintain an alarm control means 21 in an energized condition and its alarm 22 inactive.

Referring now to Fig. 2 and to the wiring diagram in detail, there is shown the alternating current power source l0 which comprises a regulating capacitor 24 in series with the primary winding of a stepdown transformer 25, the secondary winding of which provides an A.C. power source output of approximately 12 volts at 60 cycles per second.

The rectifier-filter network 11 comprises a ful-l wave selenium rectifier 26 having the output of the A.C. source l0 connected to its input legs and having a pair of voltage dividing resistors 27 and 29 in series across its output legs. The junction between the resistors 27 and 29. is grounded so that three voltage potentials are available from the network 11, for example, one across the resistor 29, at 9 volts, a second across the resistor 29 at 3 volts and a third across both resistors27 and 29 at 12 volts, namely the full output of the selenium rectifier. Filter condensers 30 and 31 are connected across the rectifier 26 output and the resistor 27, respectively, which convert 3 the pulsating output of the rectifier into a substantially constant voltage output. The standby battery l2 is connected in parallel with the output of the rectifier 1i and is trickle charged by the rectifier to maintain it at maximum potential.

The oscillaor f4 essentially includes an oscillator transformer 32 having a control winding 34, a power win-:ling 35 and a tuning winding 36; a transistor 37; and a tuning capacitor 39 connected across the winding 3o and to ground. Power is supplied to the oscillator through a conductor 4t) and passes through a variable resistor and the transistor 37 by way of the emitter-collector circuit, through the power winding 35, through the incandescent lamp l5, and finally back to the network ll by way of a conductor 42. The control winding 3d is con-- nected to the base-emitter circuit of the transistor 37 'oy way of the variable resistor l and a voltage adjusting resistor 44. A loading resistor i5 is shunted across the control winding 34- to prevent parasitic oscillation7 and a tuning capacitor 3@ shunts the tuning winding 36 to maintain the frequency at a predetermined setting. At an intermediate tap on the winding 36, a conductor 46 takes off a reference signal, returning through ground to the lower end of the tuning winding 36. This signal has a potential to maintain the alarm control 21 in an energized condition.

In order to start oscillation, an alternating current component is withdrawn from the secondary winding of the transformer 25 through a resistor 46. As current fiows through the transistor 37 and the winding 35, the winding 34 is powered by regenerative feedback from the winding 35 to provide an alternating current across the base-emitter circuit of the transistor 37. When the emitter is positive with respect to the base, the transistor conducts, but when it is negative, it does not conduct. Hence, the current through the power winding 35 is constantly in a process of starting and cutting off.

The lamp l5 is of the common incandescent filament type which in this case, provides for an indefinitely long life, and may be operated at or below 80% of its rated voltage. Incandescent lamps have an intense light characteristic, and thus may be utilized over and extended distance as compared with glow type ionized gas lamps.

The circuitry so far described includes the transmitter only. Referring now to the reciver unit, there is shown the photosensitive device i6 which essentially comprises a light sensitive transistor 457, having its elements embedded in clear plastic, and a choke 49. The collectoremitter circuit is supplied by current from the network lll through a conductor 5u, a resistor Si, the primary winding of an amplifying transformer 52 and back again to the other leg of the network il, thus being across the l2 volt output leg of the rectifier. The base-emitter circuit is supplied by a constant voltage direct current through the conductor 5f), the choke 49 and returns to the network il by way of ground, thus being connected across the 9 volt output -leg of the network lll. The capacitor 52 serves in a decoupling function, and the choke 49 provides a direct current base-emitter circuit While preventing loss of alternating current signal.

The amplifier i7 essentially consists of the transformer 52, a second transformer 54 and a transistor 55. Modulated light causes a pulsating signal from the photosensitive device 16 to flow through the primary winding of the transformer 52, and the secondary winding of the transformer 52 drives an alternating current through the base-emitter or control circuit of the transistor 55 and the by-pass capacitor 53. The emitter-collector circuit of the transistor 55 allows the passage of intermittent current from network ll by way of the conductor 56 through the primary winding of the transformer 54 and the return through the emitter and base circuits.

The phase correction network is provided by the capacitor 19 which is so selected and so connected between the secondary winding of the transformer 52 and the pri- 4l mary winding of the transformer 54 to restore the signal of the photosensitive means to the phase of the oscillator output. The secondary winding of the transformer 54 has a phase corrected alternating current output which controls the phase sensitive detector 2f).

The phase sensitive detector 2f) essentially includes a full wave rectifier 57, a transistor 59, and a group of properly selected biassing resistors 60, 6l and 62. The secondary winding of the transformer 54 provides an alternating current output which through the resistors 69, 61 and 62 biases the transistor 59. The emitter-collector circuit of the transistor 59 effectively controls the reference signal flowing through the conductor 46 into the left junction of the rectifier 57, through the resistor 52, the transistor 59, into the upper junction of the rectifier 57 and out the right hand junction. The transistor 59 is conductive during one half of the output cycle of the transformer 54 and is effectively non-conductive during the succeeding half. Therefore, when the reference signal is in phase with the corrected light signal, one half of the reference signal is allowed to pass, one half is effectively blocked. The net output from the phase sensitive detector, then, is a pulsating direct current when the system is in normal operating condition.

The alarm control means 2l is provided by a relay 64 having a filter condenser 65 across its leads. The pulsating direct current output from the phase sensitive detector 20 is altered into a straight wave form by the filter condenser 65 in order to maintain a constant direct current voltage on the relay 64. Current passing through the relay 64 returns to the lower connection of the tuning coil 36 by way of ground.

The alarm 22 may be a bell-battery circuit 66 in which the switch elements of the relay 64 are connected.

The system, thus far has been described in its normal condition in which state the photo signal, as amplified and corrected, exactly coincides in frequency and phase with the reference signal. As induced in the secondary of the transformer 54, the photosignal has a quasi-sine wave form similar to the reference signal impressed across the rectifier 57 input (left and right terminals). Leaving the rectifier 57 the reference signal voltage has a pulsating D.C. form which is fed through the collector circuit of the transistor 59 and which is mixed with the output of the transformer 54 to provide the base-emitter bias to the transistor 59. As will be noted, the addition of the photo signal voltage to the rectified reference signal voltage results in an alternating series of amplified and attenuated pulses depending upon the polarity of the corresponding pulses to be controlled. This uctuating bias voltage acts to control the fiow of current through the transistor to produce resultant alternating amplified and attenuated current pulses. Reflecting this current flow back through the rectifier, it will be seen that the resultant current flowing through the reference source will then be a wave form having attenuated positive (or negative) peaks and amplified negative (or positive) peaks. The average impressed voltage, as filtered by the capacitor 65, then results in a negative (or positive) direct current of a level sufiicient to maintain the relay in a held-in position.

In the event of loss of light at the receiver, there is no photo signal output of the transformer 54, the bias on the transistor 59 is constant and the pulsating direct current reference signal is reflected back as an alternating current quasi-sine wave through the relay and reference source, having an average direct current value of zero, and the relay 21 drops out causing the alarm 22 to energize.

lf a light of different frequency is applied to the phototransistor, the polarity of the direct current voltage across the relay would reverse at a rate equal to twice the difference between the light frequency and the reference voltage frequency. For example, if the photo voltage were 61 cycles per second and the reference voltage were 60 cycles per second, the photo voltage and reference voltage would be alternately in phase and 180 degrees out of phase once each second. This results in a momentary drop-out of the relay 21 at each reversal or, as in the above example, once per second. If the frequency difference is faster than the relay can follow, the relay will stay cle-energized.

A change in temperature doesy not cause the relay to stay energized under blocked light conditions because the successive pulses at the collector transistor 59 are increased equally with temperature. These successive pulses on lthe relay side of the rectifier are alternately positive and negative resulting in no change in the average direct current relay current.

From the foregoing description, it will be seen that the present invention provides a network having all of the advantages known heretofore in a photoelectric, tamperproof intruder system, and in addition, it allows the use of more rugged, longer lived transmitter and receiver elements without the sacrifice of using nonstandard components throughout the remainder of the system.

As various changes may be made in the form, construction and arrangement of the parts herein, without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in any limiting sense.

I claim:

1. In a photoelectric intruder system, a source of di* rect current, an oscillator having an input connected to said source and including a transformer having av power winding and a control winding, and an incandescent lamp connected to the output of .said oscillator, said oscillator including a transistor having its control circuit connected to said control winding and its output circuit connected in series with said power winding to modulate the current through said lamp.

2. A photoelectric intruder system in -accordance with claim 1, wherein said oscillator includes a tuning winding, and a capacitor is connected across said tuning winding for maintaining said output to said lamp at a predetermined frequency.

3. A photoelectric intruder system in accordance with claim l, wherein said source comprises a regulated alter- `nating current source, a transformer having its primary winding connected to said source, a full wave rectifier having its input connected vacross the output of said transformer and a standby battery connected in parallel with the output of said rectifier.

4. A photoelectric intruder system in accordance with claim 3, wherein said `oscillator includes a tuning winding, and a capacitor is connected across said tuning winding for maintaining said output to said lamp at a predetermined frequency.

5. A photoelectric intruder system comprising a direct current source, oscillator means having two outputs and an input connected to said source, an incandescent lamp connected to one of said oscillator outputs and so positioned to project light waves through a space to be monitored, phase sensitive detector means connected to the `other of said oscillator outputs, photosensitive means arranged to receive said light waves and produce signals, phase correction means having its input connected for receiving the signals from said photosensitive means and having its output connected lto said phase sensitive detector means, and normally energized alarm controlv means connected to the output of said phase sensitive detector means, whereby current is allowed to pass through said phase sensitive detector means to said alarm control means only in response to signals having a predetermined phase and frequency.

6. A photoelect'ric intruder system in accordance with claim 5, wherein said photosensitive means comprise a photo-transistor havinga constant direct current bias voltage applied toits base-emitter circuit.

7. A photoelectric intruder system in accordance with claim 5, wherein said phase sensitive detector means comprises a full wave rectifier having said other oscillator output and said alarm control means connected in series across its input, and a transistor having its ernitter-collector circuit connected across the output of said rectifier, and its emitter-base circuit connected to the output of said phase correction means.

8. A photoelectric intruder system comprising a direct current source, an voscillator having two outputs and an input connected to said source, an incandescent lamp connected to oney of said oscillator outputs and so positioned to project light waves through a space to be monitored, photosensitive means arranged to receive said light waves and produce signals, an` amplifier having its input connected to said photosensitive means, phase correction means'having its input connected to the output of said amplier, phase sensitive detector means including a rectitier connected to the output of said phase correction means and controlled thereby, and alarm means including an alarm and a relay element for normally preventing operation of said alarm, said phase sensitive detecting means having its input connected to the other of said oscillator outputs and having its output connected to said -alarm element and said phase sensitive detector means being yarranged to be conductive `between its input and its output only in response to signals of correct phase and frequency from the output of said phase correction means.

References Cited in the le of this patent UNITED STATES PATENTS l 2,099,764 Touceda Nov. 23, 1937 2,417,092 Smith Mar. 1l, 1947 FOREIGN PATENTS 716,039 Germany Jan. 12, 1942

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