GB2327493A

GB2327493A - Sighting system for temperature measuring using a pyrometer

Info

Publication number: GB2327493A
Application number: GB9813935A
Authority: GB
Inventors: Shahin Baghai
Original assignee: Omega Engineering Inc
Current assignee: Omega Engineering Inc
Priority date: 1997-06-27
Filing date: 1998-06-26
Publication date: 1999-01-27
Anticipated expiration: 2018-06-26
Also published as: CA2241761A1; CA2241761C; GB9813935D0; DE19828454B4; DE19828454A1; GB2327493B

Abstract

A sighting system for temperature measuring comprises a laser generator (1) to provide a laser beam (2), and means (3) such as a diffraction grating for dividing the laser beam (2) into at least three laser sub-beams (3a) spaced about a centre line (3b). A partially transmitting reflector (7) is arranged within the field of view of a radiometer (5). The reflector (7) transmits infra-red light from an area (9) on a target (8) whose temperature is to be measured to the radiometer, and reflects the visible light of the sub-beams (3a) to provide illuminated areas (11) disposed about the centre (10) of the area (9). In a different embodiment, a reflector transmits infra-red from a target area (19) to the radiometer, and reflects visible light to a sighting telescope (12) from a concentric area (20) slightly smaller than the target area (9).

Description

2327493 Sighting system and method for temperature measuring The present

invention relates generally to a method and apparatus for measuring the temperature of a surface using infrared measurement techniques and, more particularly, to such a method and apparatus which utilises a sighting device which is adapted respectively to aim or to project or to sense circumscribing laser or light beams for defining or showing all, or part, of the energy zone of the target, the temperature of which is to be measured.

Remote infrared temperature measuring devices (commonly referred to as infrared pyrometers or radiometers) have been used for many years to measure the temperature of a surface from a remote location. Their principle of operation is well known. All surf aces at a temperature above absolute zero emit heat in the f orm of radiated energy. This radiated energy is created by molecular motion which produces electromagnetic waves.

Thus, some of the energy in the material is radiated in 20 straight lines away from the surf ace of the material.

Many infrared radiometers use optical reflection and/or refraction principles to capture the radiated energy from a given surface. The infrared radiation is focused upon a detector, analysed and, using well known techniques, the surface energy is collected, processed and the temperature is calculated and displayed on an appropriate display.

When using such radiometers to measure surface temperature, the instrument is aimed at a target area within the energy zone on the surface on which the measurement is to be taken. The radiometer receives the emitted radiation through the optical system and is focused upon an infrared sensitive detector which generates a signal which is internally processed and converted into a temperature reading which is displayed.

The precise location of the energy zone on the surface as well as its size are extremely important to insure accuracy and reliability of the resultant measurement. It will be readily appreciated that the field of view of the optical systems of such radiometers is such that the diameter of the energy zone increases directly with the distance to the target. The typical energy zone of such radiometers is defined as where 90% of the energy focused upon the detector is. f ound.

Heretofore, determining the size of the actual energy zone is approximated by the use of a 'distance to target table, or by actual physical measurement.

It is accordingly a principal object of the present invention to provide a sighting apparatus, for use with or for incorporation into or onto a remote infrared temperature measuring radiometer, which permits coinciding of the thermometer's field of view with a visible desired area of a target the temperature of which is to be measured.

A second object of the invention is to provide such a sighting apparatus which is entirely independent of, and does not interfere with, the optical system of the thermometer.

A third object of the invention is to provide such a sighting apparatus which is readily mountable on, and dismountable from, the thermometer.

A fourth object is to coincide the line of sight of the system with the line of optical f ield of view, to allow more accurate sighting when aiming at different targets.

Against the foregoing background, in general terms of a f irst form of the present invention provides a sighting system, for temperature measuring apparatus using infrared techniques, which utilises a laser generator to provide a laser beam which becomes at least three laser sub-beams spaced about a center line, which sub-beams are aimed onto a reflector arranged within the field of view of the radiometer, said reflector being selected to (a) transmit infrared light, and (b) reflect laser light and visible light, said reflector being positioned to direct the subbeams to the target in such a manner as to provide small visible illuminated areas (e.g. 'spots') disposed about the center of that area of the target whose temperature is to be measured.

In a further feature, the apparatus is arranged to provide additionally a further sub-beam, which is axial to the above-mentioned sub-beams and which accordingly provides an illuminated 'spot' at the center of the target area.

In a second form, light rays emanating from an area of the target, concentric with the area whose temperature is to be measured, are,passed to a reflector which again is selected to (a) transmit infrared light and (b) reflect visible light. Infrared rays emanating from the selected target area pass unchanged through said reflector and are concentrated by an infrared lens into an infrared detector. Visible light rays emanating from the concentric area are deflected by the reflector to an optical system such as an angled mirror which directs them to an optical sighting device such as a sighting telescope.

The invention thus concerns, firstly, a sighting system for temperature measuring which comprises, for inclusion in an optical path between a selected area of a target, whose temperature is to be measured and a radiometer which assesses that temperature, a deflector which is transparent to infrared rays emanating from the target area but is reflective of laser light rays, and means for generating a plurality of laser light beams onto said deflector so as to be directed by said deflector along said optical path to strike the target and visually identify at least an outline of said selected area.

Secondly, the invention concerns a sighting system for temperature measuring which comprises, for inclusion in an optical path between a selected area of a target, whose temperature is to be measured, and a radiometer which assesses that temperature, a deflector which is transparent to infrared rays emanating from the target 1 area but is reflective of visual light rays, and an optical sighting means positioned to receive light rays from said deflector for viewing and thereby visually identifying at least an outline of said selected area of the target.

Thirdly, the invention concerns a method, for visually identifying at least an outline of a selected area of a target whose temperature is to be measured by passage of infrared rays along an optical path from said selected area to a radiometer, said method comprising deflecting into said optical path, by means of a deflector which is transparent to infrared rays, a plurality of laser beams to strike the target to at least outline said selected area visually.

Fourthly, the invention concerns a method, for visually identifying at least an outline of a selected area of a target whose temperature is to be measured by passage of infrared rays along an optical path from said selected area to a radiometer, said method comprising deflecting out of said optical path, by means of a deflector which is transparent to infrared rays, light rays emanating from said selected area of the target, and passing said deflected light rays to an optical sighting means.

The foregoing and still other objects and advantages of the present invention will be apparent from the detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawings, wherein: Figure 1 is a schematic longitudinal section of a f irst embodiment of the invention utilising laser light for target illumination; 5 Figure 2 is a f ront elevation of a part of a target on which a pattern of spots is provided by the apparatus; Figure 3 is a schematic longitudinal section of a second embodiment of the invention utilising visible light for target sighting; Figure 4 is a front elevation of part of a target to be sighted; Figure 5A is a diagrammatic side elevation of the improved sighting system utilising a laser; Figure 5B is an elevation to show the pattern of laser light dots received on the target; Figure 6A is a diagrammatic side elevation of the improved sighting system utilising a sighting telescope; Figure 6B is an elevation to show the view of the target obtained with the system of Figure 6A. An important aspect of the invention is that it provides, for use with a radiometer adapted to assess the temperature of a selected area of a target, an attachable and separable module which can visually delineate that selected area, as by an outline or a field of view corresponding to all or part of the selected area, by insertion of a visual-light or laser- light deflecting means into an infrared path between the selected area of the target and the heat sensing means of the radiometer, without changing or disturbing the normal operation of that infrared path and said heat sensing means.

Referring to Figures 1 and 2 of the drawings, there is shown a f irst embodiment of apparatus in accordance with the invention. A laser generator module 1 produces a single laser beam 2 which is passed through a beamsplitting means 3 which may be, for example, a diffraction grating, a beam splitter or a prism. The beam- splitting means 3 is constructed so as to cause the single laser beam.2 to be sub-divided into a plurality of divergent sub-beams, and specifically into twelve sub-beams 3a which are symmetrically arranged in a circle, and a single central sub-beam 3b. The plurality of sub-beams 3a, 3b pass to a mirror 4 disposed at 4 degrees to direct them onto an infrared filter/mirror 7 which has properties of (a) transmitting infrared rays, and (b) reflecting laser light. Means (not shown) may be provided to adjust the position of the mirror 4 mechanically, e.g. by a motor drive or adjusting screw.

The temperature measuring apparatus is shown only schematically, and includes an infrared detector 5 associated with an infrared lens 6.

A target 8, whose temperature is to be measured, sends infrared rays towards the infrared lens 6, and this concentrates the received rays onto the detector 5. The area 9 of the target which is sensed by the combination 5-6 is circular. The infrared filter/mirror 7 directs the collection of sub-beams 3a,3b towards the same circular area of the target, and def ines that circular area on the target by a circle of illuminated spots, 11. The central sub-beam 3-b also strikes the center of the target area at 10. It is to be noted that the central sub-beam 3-b can be omitted, and then only the circular arrangement of subbeams 3a used.

For the user of the apparatus, it is then immediately apparent which circular area of the target is being measured for temperature because that area is outlined by clearly visible spots 11.

Referring to Figures 3 and 4 of the drawings, the sighting method is effectively reversed. A sighting telescope 12 is disposed in alignment with a lightref lecting mirror 13 which ref lecits to the telescope 12 the light rays 14 which are directed to it by an infrared filter/mirror 15 which has the properties of (a) transmitting infrared rays, and (b) reflecting visible light.

Here again, the temperature measuring apparatus is shown only schematically, and includes an infrared detector 16 associated with an infrared lens 17. The target 18, whose temperature is to be measured, sends infrared rays towards the infrared lens 17, and this concentrates the received rays onto the detector 16. The area 19 of the target which is sensed by the combination 16-17 is circular. A concentric, but slightly smaller, area 20 of the target sends visible rays 14a to the infrared filter/mirror 15, so that the user viewing through the sighting telescope 12 sees the circular area 20 and thus knows that.the heat-sensing means is centered appropriately on that part of the target which is to be sensed for temperature measurement.

In both embodiments, the filter 7 or 15 could have optical properties such that it transmits infrared energy in the bandwidth of 8 to 14 microns.

It is a further feature of the invention that the detecting and aligning system consisting of items 1, 3, 4 and 7 in Figures 1 and 2, and consisting of items 12, 13 and 15 in Figures 3 and 4, could be made mountable and dismountable with respect to the remainder of the apparatus.

An essential feature, common to both of the embodiments described, is the use of light/laser mirror means inserted into the infrared transmission path for deflecting the 'sighting, rays into or out of the infrared path without affecting the latter.

In both embodiments, the goal to be achieved is to ensure coincidence between what the user sees, and the area of the target which is being sensed for temperature, i.e. to provide easy and accurate aiming of the radiometer. It is an advantage that this sighting system does not interfere with the radiometer's own optical system. As a result, the sighting system can be manufactured independently of the radiometer, and, can be added to the radiometer as required, and this provides better control of manufacturing and stock.

Figure 5A shows a laser sighting system and in detail shows how the sighting system is designed. The laser module 101 provides a collimated laser beam 102. The laser beam hits a Diffraction Grating Lens 103. The diffraction grating lens splits the collimated laser beam into a number of laser beams which are deflected on an angle. The accumulation of the spread laser beams provides a laser circle affect. The spread laser beams hit a 45 degree angle mirror 104 which reflects the laser beams to an infrared filter 107. The infrared filter 107 has optical properties such that it transmits the infrared energy in the bandwidth of 8 to 14 microns; and it reflects visible light as well as laser light. Because of such properties the spread of laser beams is refelected off the infrared filter and projects a series of laser dots on the target being measured 108 to form a laser circle 111. The actual field of view 109 of the thermometer may be slightly larger than the laser circle 111. If there were no diffraction grating lens 103 then the laser module would project a single laser dot 110 which is an indication of the center of the target being measured. The infrared energy from the target goes through the infrared filter 107 and is collected by the infrared lens 106. The infrared lens then focuses the incoming energy on the active area of the infrared detector 105.

In a further embodiment, Figures 6A, 6B show a sighting system that instead of using a laser module, uses i a sighting scope 112. The rest of the sighting system is the same as in Figures.5A, 5B. The sighting scope viewing area 113 is slightly smaller than the actual field of view of the thermometer 109.

In both embodiments of sighting systems, the object is to coincide the thermometer's field of view with the line of sight for more accurate aiming. Another advantage of the design is that the sighting system does not interfere with the thermometer's optical apparatus. As a result, the infrared thermometer can be manufactured independently of the sighting system. The sighting system can be added later on as required. This provides better control of manufacturing and stock.

claim:

1. A sighting system and method for temperature measuring comprising a laser generator to provide a laser beam, means for dividing said laser beam into at least three laser sub-beams spaced about a center line, a reflector arranged within the field of view of a radiometer, said reflector being selected to transmit infrared light and to reflect laser light and visible light, said reflector being positioned to direct said sub- beams to a target to provide on said target visible illuminated areas disposed about the center of an area of said target whose temperature is to be measured.

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