Pyrodetector

Details Pyrodetector Pyrodetector

1981-07-27

1983-09-13

Howell, Janice A.

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

250347, 250349, G01J 100

Patent

active

044044682

ABSTRACT:
A pyrodetector is disclosed which has a sharply limited directional range of detection sensitivity for the detection of a body entering into its directional range at a distance from the detector, the body having a temperature which is different from that of its environment. A concave mirror for focusing thermal radiation emanating from the body is provided and a pyroelectric sensor positioned at a focus of the mirror is also provided and formed as a flat body consisting of an electrically non-conductive material and with a pair of electrodes. A cover transmissive to the incident thermal radiation is provided for protecting the sensor element against damage and air drafts. At least one further sensor element similar to the first sensor element and with essentially the same heating time constant is also provided and arranged adjacent to the first sensor element but beyond the mirror focus. The electrode pairs of all the sensor elements are connected to an electrical evaluation circuit which forms a difference between an output signal of the first and further sensor elements. The pairs of electrodes are each terminated with an impedance such that a time constant K of a decay time of the sensor element R.sub.x .multidot.C.sub.x =K is valid for all pairs of electrodes where C.sub.x is a capacitance of the capacitor formed from a respective pair of electrodes, R.sub.x is the respective terminating impedance, and K<10 seconds. In a preferred embodiment of the invention a honeycomb grating is provided directly adjacent the transmissive cover which protects the sensor elements.

REFERENCES:
patent: 2855492 (1958-10-01), English, Jr.
patent: 3839640 (1974-10-01), Rossin
patent: 3877308 (1975-04-01), Taylor
patent: 4225786 (1980-09-01), Perlman
patent: 4275303 (1981-06-01), Mudge

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