Radiant energy – Photocells; circuits and apparatus – Signal isolator
Patent
1997-11-07
2000-04-25
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Signal isolator
2502033, 2502062, G01B 1126, G01J 120
Patent
active
060547154
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a radiation sensor for determining the direction of incident radiation. The starting point has especially been to provide a radiation sensor of the type concerned that can be used in military laser warning contexts. However, the radiation sensor can of course also be used in other contexts.
BACKGROUND OF THE INVENTION
One of the difficulties when constructing laser warning devices consists in the mastering of the great dynamic range of the incident light intensity. The range within which one could want the warner to function is within the irradiance extremes 10 mW/m.sup.2 and 10 GW/m.sup.2, i.e. the dynamic range amounts to 120 dB. If a range from 10 W/m.sup.2 to 1 GW/m.sup.2 is sufficient, the dynamic range will be 80 dB, which may be said to be a more reasonable value, but still a range that is technically difficult to measure. In addition to this difficulty, the illumination is in most cases pulsed and the pulses are very short (nanoseconds).
There are different ways of solving the problem. Signal processing that is based on the measuring of illumination-analog signals requires, for reasons of dynamics, a plurality of detectors and a plurality of signal paths. For each signal path, advanced electronics requiring great accuracy is necessary. If, on the other hand, one tries to build a signal receiver that functions digitally in the sense that illumination towards a detector produces a single type of response if the selected threshold value is exceeded, 360 detectors with signal processing are necessary if, for instance, an angular resolution of 1.degree. is desired all around. The alternatives seem to be exacting electronics and a relatively large number of detectors or simpler signal processing, but then for a considerably larger number of detector signals.
If incident illumination can somehow be made to fall along a line, the illuminated position depending on the direction of incidence, it would be possible to use a position sensing detector (PSD) of commercial type. A one-dimensional PSD is an elongate photodetector of special design, in which the generated photocurrent is conducted in two separate paths. The position of the illumination is determined by measuring the currents delivered at the two ends of the PSD and calculations on the basis of these measured values. The relative size of these currents is determined by the difference in internal resistance between the illuminated point and the two current supply points of the PSD. The ratio of the difference to the sum of the two measured currents gives the position along the longitudinal axis of the detector. However, PSD detectors are not intended for so short pulses as those involved in laser warning contexts and, besides, their dynamic range is restricted, which means that commercially available detectors of this type cannot be used for the intended purpose.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 is a basic sketch of a sensor according to the invention,
FIG. 2 illustrates an embodiment of a sensor according to the invention,
FIG. 3 is a diagram of measured values of different angles of incidence for a sensor according to the invention, a straight line being drawn, which represents the ideal outcome,
FIG. 4 is a diagram of measured angular errors at different angles of incidence in the above graph,
FIG. 5 illustrates a first embodiment of a sensor construction according to the invention having a lens element,
FIG. 6 illustrates a second embodiment of a sensor construction according to the invention having a lens element, and
FIG. 7 illustrates a third embodiment of a sensor construction according to the invention having a slit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The basic idea in the invention is to create, by discrete elements, a PSD-like sensor construction, see FIG. 1, in which photodiodes are designated D and resistors R and R.sub.a. With such a construction,
REFERENCES:
patent: 4315690 (1982-02-01), Trocellier et al.
patent: 4914283 (1990-04-01), Brinckmann et al.
patent: 5103088 (1992-04-01), Halldorsson et al.
Mannerskog Gunnar
Nissborg Kurt
Allen Stephone B.
Simrad Optronics ASA
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