Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1984-02-03
1986-10-21
Rowland, James L.
Communications: electrical
Condition responsive indicating system
Specific condition
250342, 250349, G08B 1318
Patent
active
046188541
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a double eye type crime preventing sensor system and particularly to a (double twin) sensor system wherein two pairs of sensors (twin sensor systems) are disposed in two horizontal rows one above the other along a direction in which persons or objects come in.
BACKGROUND ART
The system that has been frequently used in recent years in sensing devices in entry warning systems is such that two pyroelectric sensors made of ferroelectric substance are horizontally arranged and their output terminals are connected in series or parallel to provide a differential output. Since two detection axes for two sensors (usually the incident axes of concave mirrors for causing extreme infrared rays from an object to be focused on these sensors, or incident axis from the light source to the sensors when near infrared rays or other visible light rays are used) are spaced tens of centimeters at a maximum from each other along a direction in which objects to be detected come in, when a person or an object moves in that direction or in the opposite direction across the detection axes, signals of opposite polarities will be successively produced. However, when a falling object crosses the two detection axes at the same time, the resulting two sensor outputs cancel each other, so that the resultant signal is zero. Thus, in the twin system, a warning can be produced when a person or the like successively crosses term at the level of disposition (detection level) of the two sensors.
The twin system is capable of detecting the direction of movement in a horizontal plane in this manner, as compared with the single eye system, but it has the disadvantages that it cannot judge the height of an entering object and that detection with mere two points (two eyes) is subject to the influence of a disturbance, that is, in twin sensors, if an insect or a small animal or some object moves in the direction of disposition of the sensors at their level of disposition (or detection level), a warning will be issued (erroneous warning). Although detection with only two points is not influenced by substantially uniform air cooling which covers these points, there is a danger that an erroneous warning is produced in response to the cooling or heating of only one point by a draft or direct sunlight, or that reversely an entering person or the like is overlooked.
DISCLOSURE OF THE INVENTION
The present invention is intended to eliminate the drawbacks of the aforesaid conventional twin sensor system and provides a crime preventing sensor system wherein two pairs of sensors are disposed in two horizontal rows one above the other along a direction in which objects come in. The detection levels provided by the twin sensors in the upper and lower rows may be made to correspond to the levels of the breast and either the loins or the legs of a grown-up man, and the signal processing circuit is arranged to produce a warning output when the differential outputs from the respective rows are in phase with each other.
Therefore, according to the present invention, even is a small animal passes by, only the twin sensors in the lower low are actuated, so that no warning signal is produced, while the outputs from the two rows due to differences in detection temperature in the twin sensors caused by a draft or direct sunlight are out of phase with each other and are rarely produced at the same time, so that there is little possibility of an erroneous warning being produced owing to these disturbances.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side sectional view showing an example of disposition of a detection system for crime preventing sensor system according to the present invention;
FIG. 2 is a block diagram of a signal processing circuit in the embodiment;
FIG. 3 is a circuit diagram showing the principal portion of the signal processing section; and
FIG. 4 is a waveform diagram showing the relation between input signals and arithmetic outputs.
BEST MODE OF CARRYING OUT THE INVENTION
FIG. 1 is a side view
REFERENCES:
patent: 3760399 (1973-09-01), Schwarz
patent: 3958118 (1976-05-01), Schwarz
patent: 4052716 (1977-10-01), Mortensen
patent: 4364030 (1982-12-01), Rossin
"Performance of Narrow-Field, Passive, Infrared Intrusion Detector", Proceedings of the Society of Photo-Optical Instrumentation Engineers Seminary, Sep. 1972, Schwarz.
Makino Masami
Miyake Ryota
Rowland James L.
Takenaka Engineering Co. Ltd.
Tumm Brian R.
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