Dual field of view intrusion detector

Abstract

Abstract An intrusion detector for detecting movement of bodies radiating in the infrared in a space to be monitored is a combination of an infrared detector such as a thermopile, thermistor, or pyroelectric detector in which a series of all-active thermocouple junctions or pyroelectric detectors connected in opposition is arranged in alignment so that columns of junctions are of alternating polarity, so that an object moving in the space and radiating in the infrared, the image of which moves across the columns, will produce an AC signal which is then amplified and processed electronically to produce an alarm. The electronic circuits, including logic, are well known, and their particular design forms no part of the present invention. Instead of having a single optical system, such as, for example, a germanium lens, imaging the body on the plane of the detector, there are two optical systems, preferably on different focal lengths, one of which images on the front of the detector and the other on the back. The imaging on the back may be reflective, so that intensified images are produced, or it may employ a refracting element for imaging on the back of the detector. In the former case, sensitivity is greatly increased, for example, doubled, and in the second case, which can be used for a detector in long, narrow spaces such as corridors, the sensor can be placed in the middle and will respond to moving bodies on either side of the detector. If it is desired to have a denser coverage of image so that to some extent the spaces between the columns are filled in, in this case the optics is adjusted so that a slightly different field of view is imaged on the back of the detector. This means that a moving object would have to be much smaller or move a lesser distance in order not to strike columns. The sensitivity of course is not increased in such a case.

Inventors

• 👤 F Schwarz

Bibliographic Details