Thermal measuring and testing – Thermal calibration system – By thermal radiation emitting device
Patent
1992-02-14
1993-11-30
Cuchlinski, Jr., William A.
Thermal measuring and testing
Thermal calibration system
By thermal radiation emitting device
2504951, 2502521, G01K 1500, G01D 1800
Patent
active
052659585
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a testing device for thermal imagers and a method of testing thermal images.
2. Discussion of Prior Art
Thermal imagers test methods and apparatus are well known in the prior art. They generally require access to temperature controlled, substantially draught free environments in special purpose laboratories. They can be used to test imagers for minimum resolvable temperature difference (MRTD) or minimum detectable temperature difference (MDTD).
A typical prior art testing apparatus incorporates a set of pattern plates, usually five or more, for viewing by a thermal imager. Each plate has a respective pattern, and the patterns differ in spatial frequency. In use the plates are positioned one at a time in front of a heating/cooling element consisting of a high emissivity plate connected to a heating/cooling device, usually a peltier device. Such high emissivity plates are usually referred to as blackbodies, although strictly speaking their emissivities are slightly less than unity. The heating/cooling element is viewed through the pattern plate firstly when hot and secondly when cold relative to ambient temperature. The temperatures are adjusted manually.
Each plate is thus viewed twice and the test is time consuming. A curve of MRTD or MDTD versus spatial frequency is obtained, but the test does not provide a quick assessment of whether the thermal imager passes or fails. The most limiting factor however is the necessity to perform the test in a temperature controlled, substantially draught free laboratory environment. In addition the prior art method requires expensive apparatus, including the use of a radiometer to calibrate the system prior to use. There is no apparatus or method available in the prior art to enable realistic tests to be carried out in the field.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an alternative device and method for testing thermal imagers. The present invention provides a testing device for thermal imagers including a viewing element characterised in that: respective patterns of like spatial frequency, and temperatures of the first and second emission regions such that they are observable as above and below a background temperature respectively when viewed by a thermal imager.
The invention provides the advantage that it enables a rapid assessment of thermal imager performance to be made, by observation of two or more patterns. Where appropriate the patterns may be viewed simultaneously. Alternatively the patterns may be viewed in rapid succession, each being positioned automatically in the field of view as required. It is susceptible to construction with reduced size and cost compared to the prior art, and it does not require to be used in a temperature controlled, substantially draught free laboratory environment.
In a preferred embodiment additional thermal emission regions are provided on the viewing element in order to test the imager performance over a range of spatial frequencies and associated temperature differences.
The invention may be constructed with fixed temperature differentials between the first and further thermal emission regions. This enables GO-NOGO tests of thermal imager performance to be carried out very simply and rapidly.
The invention may also include circuitry for increasing the temperature differentials by a prearranged percentage. This enables a second less rigorous test to be conducted to assess whether imagers are part functional or non-functional.
The invention may include means by which the effective temperature of each thermal emission region may be manually adjusted. This enables full MRTD or MDTD tests to be carried out more rapidly than in the prior art.
The viewing element may be a pattern plate through which patterns are cut to define the thermal emission regions. The effective temperatures of the patterns may be provided by thermally emissive elements viewable through the patterns.
The invention may be constructed such th
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Cuchlinski Jr. William A.
Gutierrez Diego F. F.
The Secretary of State for Defence in Her Britannic Majesty's Go
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