GB2203537A

GB2203537A - Measuring radiation from articles

Info

Publication number: GB2203537A
Application number: GB08805687A
Authority: GB
Inventors: Ullrich Demisch; Thomas Springmann
Original assignee: Testoterm Messtechnik Co GmbH
Current assignee: Testoterm Messtechnik Co GmbH
Priority date: 1987-03-30
Filing date: 1988-03-10
Publication date: 1988-10-19
Anticipated expiration: 2008-03-10
Also published as: FR2613483B1; JPS63255630A; FR2613483A1; DE3710486C1; GB2203537B; GB8805687D0

Description

1 1r.' C- n n, C, J "AN APPARATUS FOR MEASURING RADIATION11.

The invention relates to an apparatus for measuring radiation emanating from an article, typically exemplified by infra-red radiation pyrometers.

Such devices are frequently used for measuring temperatures in inaccessible positions or temperatures at ranges in which thermoelectric cells or resistance thermometers cannot be used.

Problems are often encountered with targetting the thermometer so that it is directed to the precise spot or area at which the temperature is to be measured, particularly when using infrared radiation pyrometers. For this purpose, a frequently used aid for targetting the pyrometer is to create a target area, for example by use of a spot of light which is projected onto the article from which the radiation emanates. it is also possible to determine the exact adjustment using a ranging rod and a slip-on lamp or using a sighting cone.

However, the last-mentioned arrangements which involve mainly mechanical means are suitable only for relatively short distances from the article whose temperature is being measured. Furthermore, simultaneous sighting and measuring are not possible when using ranging rod and slip-on lamp.

Reflection of a light spot onto the optical axis, for example via a half-silvered mirror, is accompanied by the disadvantage that the measuring lens must be transparent to visible light. It is also possible that the measured value may be distorted by the visible light. The use of a telescopic sight necessitates a complex lens system, adjustment, as well as signal losses through half-silvered mirrors, as the display has to be brought into the field of vision of the viewfinder for simultaneous sighting and measurement. If laser optics are used, expenditure and space requirements are further increased.

2 U.S. Patent No. 4 315 150 describes a targetted infrared thermometer in which there is provided, parallel to the actual radiation measuring device, a laser tube which, by means of a double lens system arrange partially in the optical axis of the laser-tube and partially in the optical axis of the radiation measuring device, produces two luminous circular beams (or target areas) of differing diameter and differing brightness which, if oriented concentrically, are arranged exactly in the contre of a circular measuring region which surrounds them and is focused onto the receiving surface of the radiation measuring device. This arrangement is relatively bulky because, in addition to the actual radiation measuring device, a laser tube of approximately equal size as well as a double lens system are required, the rays produced by the double lens system being at a relatively great distance from one another so that the space required for inaccessible measuring positions is often unavailable. Moreover, the actual target area of the radiation measuring device is a circular area, whereas it is often desirable to measure the temperature in a very small, almost dot-shaped target area.

The object of the invention is to provide a radiation measuring apparatus which can be located accuritely on the desired target area and simultaneously measure its temperature, without distorting the temperature to be measured, the apparatus having a simple structure and small space requirement.

According to the present invention there is provided an apparatus for measuring radiation emanating from the surface of an article, said apparatus comprising a radiation detector incorporating a Cassegranian focus type reflector system, and a lens system for projecting an image on to the said surface of the said article for the purpose of orienting and locating the apparatus relative to the said article, the lens system being positioned so that it is on the optical axis of the Cassegranian reflector system in the optically unused central region thereof, the lens system further including a light source and, in the path of the light source, a disc-shaped masking 3 patch which is opaque to visible light and is imaged on to the said article, the size and position of the masking patch being chosen so that its image on the said article co-incides with the size and position of the image of the receptor of the radiation detector.

The apparatus of the present invention provides a compact unit, space requirements being reduced to a minimum by the exclusive use of the space in the dead angle of the lens system. By means of the present invention in which the image of the masking patch appears as an unilluminated circular target area surrounded by a ring of light, distortion of the test results is eliminated.

In a preferred embodiment of the present invention the masking patch is positioned on or in front of a light source in particular on the tip of a luminescent diode used as light source; this arrangement further simplifies the device and reduces the space requirements.

The construction of the adjustable levelling device using fewer and simpler components produces extremely high stability, for example during impacts, owing to the high coefficients of friction between the pressed on special plastics material and the supporting surface.

An embodiment of the present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 shows a simplified sectional diagram through an infrared radiation pyrometer in accordance with the invention, showing the optical path of the light rays, and Figure 2 shows a schematic illustration of a luminescent diode acting as light source with a masking patch inserted in its tip.

Referring to Figure 1, there is shown an infrared radiation pyrometer designated generally by the reference numeral 10 which 4 comprises a Cassegrain telescope reflector system 12, a radiation detector 14 and a lens system 16 for generating a targetting image in accordance with the invention. In the radiation detector 14 there is arranged a receiving surface 18 which detects the energy irradiated by an object (not shown) whose temperature is to be tested and tansmits it for measurement purposes. The image from this receiving surface 18 is represented, via secondary mirror 20 and main mirror 22 of the Cassegrain reflector system 12, as a target area 24 for temperature measurement on the surface of the object whose temperature is to be measured.

The purpose of the lens system 16 for generating a targetting image is to determine the precise position and also the diameter of the target area 24 on the object whose temperature fs to be determined as the target area 24 is not visible as such and the use of expensive telescopic sights or other optical systems is to be avoided. For this purpose, a light source 26 whose beam of light is directed via a lens 28 onto the surface of the article is provided in the lens sytems 16.

The entire lens system 16 is arranged on the rear of the secondary mirror 20 in the dead angle of the path of rays from the Cassegrain telescope reflector system 12 and lies on the optical axes thereof.

By suitable arrangement of the lens 28, the image distance of the masking patch 30 can be made to coincide with that of the receiving surface 18 of the radiation detector 14.

To prevent the test result from being distorted by the illumination of the target area 24 with visible light, there is inserted between the light source 26 and the lens 28 a masking patch which is opaque to visible light and blanks out a central circular area of the light beam from the light source 26 so that only a ring of light surrounding this circular area remains visible. The size and position of the masking patch are selected such that its image on the article whose temperature is to be measured is identical to the image of the receiving area 18 of the radiation detector 14.

In a preferred embodiment of the invention, the light source 26 is a luminescent diode 32 whose tip has a circular recess filled with a material 36 which is opaque to the light irradiated from the luminous surface 34 of the luminescent diode, as shown schemati-cally in Figure 2. The material 36 which is opaque to light forms the masking patch 30, the diameter of which is determined by the diameter of the recess in the tip of the luminescent diode 32 and is adapted to the diameter of the target area 24.

For precise adjustment of the lens system 16 relative to the optical axis of the Cassegrain telescope reflector system, the lens system is fixed on a sprung plate 38 composed, for example, of special-grade plastics material. with three adjusting screws 40 arranged in a triangle by whose adjustment the lens system is tilted until the image of the masking patch 30 coincides with the image of the receiving surface 18 of the radiator detector 14. The elastic properties and the coefficient of friction of the special-grade plastics material used for the sprung plate 38 are selected such that maximum stability and insensitivity, for example, to shock loads, are ensured.

During use, the position'of the infrared radiation pyrometer with respect to the surface whose temperature is to be measured and the distance from said surface are varied until the image of the masking patch 30 or the ring of light 42 surrounding it appears distinctly at the desired location on the surface whose temperature is to be measured. As a result the smallest targetting area for the infrared radiation pyrometer is established with certainty and ensures that the receiving surface 18 of the radiator detector 14 only absorbs the heat radiation to be measured.

6

Claims

CLAIMS:

I. An apparatus for measuring radiation emanating from the surface of an article, said apparatus comprising a radiation detector.

incorporating a Cassegranian focus type reflector system, and a lens system for projecting an image on to the said surface of the said article for the purpose of orienting and locating the apparatus relative to the said article, the lens system being positioned so that it is on the optical axis of the Cassegranian reflector system in the optically unused central region thereof, the lens system further including a light source and, in the path of the light source, a disc-shaped masking patch which is opaque to visible light and is imaged on to the said article, the size and position of the masking patch being chosen so that its image on the said article co-incides with the size and position of the image of the receptor of the radiation detector.
2. An apparatus according to claim 1, wherein the masking patch is located on or in front of a light source.
3. An apparatus according to claim 2, wherein the masking patch is located on the tip of a luminescent diode acting as the light source.
4. An apparatus according to claim 3, wherein the tip of the luminescent diode has a recess, the diameter of which corresponds to the diameter of the masking patch and which is lined with a material which is opaque to visible light.
5. An apparatus according to any one of the preceding claims, further comprising an adjustable levelling device comprising a spring plate of elastic plastics material, against which the lens system is pressed in tilting manner by three screws.
6. An apparatus according to claim 1, substantially as hereinbefore described with reference to the accompanying drawing5.

Publiblied 1988 at The Patent Office, State House, 86171 High Holborn, London WCIR 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.