GB2173297A

GB2173297A - Constant light pyrometer

Info

Publication number: GB2173297A
Application number: GB08606608A
Authority: GB
Inventors: Dr Franz Engel; Dr Bernd Hebmuller; Jorg Gunther; Eckbert Kenzler; Norbert Rose
Original assignee: WEINERT E MESSGERAETEWERK
Current assignee: WEINERT E MESSGERAETEWERK
Priority date: 1985-04-03
Filing date: 1986-03-18
Publication date: 1986-10-08
Also published as: DE3603464A1; DE3603464C2; GB8606608D0; GB2173297B

Abstract

A constant light pyrometer for contactless measurement of the temperature of test objects requiring exact sighting, for example small or distant objects, which can reflect daylight or artificial light, achieves alignment of the pyrometer during measurement without the sample radiation in the infrared spectral range to be evaluated being weakened and without ghost images being formed in the field of view of the pyrometer. A selective mirror 3 is disposed obliquely in the beam path of the pyrometer which divides the impinging radiation spectrally in such a way that at least one portion of the visible radiation is reflected and the sample radiation to be evaluated for temperature measurement 4, 5, 6, 7 is allowed to pass. The selective effect of the mirror 3 is achieved by the application of one or more optical layers on the front and back surface of the mirror or on its front surface. The visible radiation portion is passed to a sighting device 14 so that the pyrometer can be aligned on the test object. Alternatively the mirror 3 may pass the visible radiation and reflect the infrared. The sighting device may alternatively comprise a means for illuminating a spot on the object. <IMAGE>

Description

SPECIFICATION Constant light pyrometer The invention relates to a constant light pyrometer for contactless measurement of the temperature of test objects requiring exact sighting, for example small or distant objects, and which can reflect daylight or artificial light.

Changing light pyrometers are known, from German Auslegeschrift No.1473259 (1964), in which a movable oscillating mirror is mounted in the beam path. This oscillating mirror is used to carry out both sighting and modulation of the sample radiation. Additional filters can be used in the beam path for isolating the sample radiation. This is technically complex and thus not inexpensive. Furthermore, the arrangement has movable mechanical parts, which reduces its reliability.

Constant light pyrometers, however, do not have these disadvantages. One technical soiution is provided by constant light pyrometers which use partially reflecting mirrors (Siemens Ardofot radiation pyrometer, Siemens MP 11/1977) for installing a sighting device. This type of solution has the disadvantage that part of the sample radiation has to be used for sighting and thus cannot be measured. Possibilities for reducing the reflected portion are limited by the necessity for contrast in the field of vision and for suppression of ghost images by the mirror back surface.

Selective action must be obtained by the use of additional filters.

Furthermore, constant light pyrometers are known (DD 61360), which use a bored reflecting disc as a field stop in the beam path. In comparison to the partially reflecting mirror, this device has the advantage that none of the sample radiation is used for sighting. However, the field to be measured is visible only as a black spot and its structure cannot be seen in the field of vision. Additional filters must again be used to carry out selection and isolation.

It is a basic object of the present invention substantially to eliminate the above-mentioned disadvantages of the known technicai solutions.

In particular, it is an object of the present invention to provide a constant light pyrometer which enables alignment of the pyrometer during measurement without unnecessarily weakening the sample radiation in the infrared spectral range to be evaluated and without allowing ghost images to occur in the field of view of the pyrometer. It is a further objective of the invention to reduce the influence of the lamp or sun radiation reflected by the test object and to ensure that the test object is visible across the entire field of view.

In accordance with the present invention, by means of a selectively acting mirror, the heat radiation from the test object falling into the constant light pyrometer and focussed by means of collecting optics is spectrally divided in such a way that at least one part of the visible radiation is reflected and the sample radiation to be evaluated for temperature measurement is allowed to pass, or such that at least a part of the visible radiation is allowed to pass and the sample radiation to be evaluated for temperature measurement is reflected.

The visible radiation spectrally divided by the selective mirror is passed to a sighting device. The test object can be observed and can be aligned for marking by means of an eyepiece, which is a component of the sighting device. As the short-wave radiation is not measured, the influence of lamplight or sunlight (in the measuring area) on temperature measurement is reduced.

The sample radiation in the infrared spectral range to be evaluated, which has been spectrally divided with high transparency by the selective mirror, passes either directly to the radiation detector or is focussed beforehand onto a field stop. The selective mirror is disposed obliquely in the beam path of the pyrometer, and one or several optical layers are applied to its front surface or to its front and back surfaces.

The selective mirror may also comprise an infrared interference.

Application of the invention allows, by means of an optical component, the attainment of the desired isolation as well as an optimum beam division for the sample beam path and the sighting beam path of the pyrometer. This solution is very inexpensive.

There are no ghost images in the field of view of the pyrometer which might impair sighting. Furthermore, the entire field of view is equally visible. No sample radiation energy is expended on sighting. The influence of the short-wave radiation reflected at the test object is reduced (for example sunlight, lamp radiation).

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a constant light pyrometer with a selective mirror, in which a part of the visible radiation is reflected; Figure 2 shows the constant light pyrometer of Fig. 1, in which a pilot lamp is used as a sighting device; Figure 3 shows a constant light pyrometer with a selective mirror, in which a part of the visible radiation is allowed to pass; and Figure 4 shows the spectral reflection or transmission curve for a constant light pyrometer as shown in Fig. 1.

In Fig. 1, the heat radiation transmitted by the test object 1 is focussed by collecting optics 2 and passed to a selective mirror 3 disposed obliquely to the beam path. The sample radiation to be evaluated for temperature measurement is allowed to pass by the selective mirror 3 and is focussed on a field stop 4 having a radiation detector 5 disposed beyond it. The radiation detector 5 is connected to an information processing unit 6 and a temperature indicator 7. The visible radiation portion reflected by the selective mirror 3 passes to sighting device consisting of a field lens 8, a path-folding mirror 9, an erecting lens 10, a filter 11, a field stop 12, a graticule 13 and an eyepiece 14.This visible radiation portion serves to form an image of the test object 1 and its surrounding medium in the sighting device, whereby the filter 11 facilitates the sighting of glowing test objects by reducing their brightness and indicates the size of the test spot to the observer by a circle on the graticule 13.

The selective mirror 3 has a holder 15 which can, for example be a glass plate. An alternating layer system 16, consisting of Si O2 and Ti 02, has been applied to the holder 15 in a combination H/2 (LHLHLHLHL) H/2, whereby H is a layer with a high refractive index, and L is a layer with a low refractive index.

In Fig. 2, the sighting device in Fig. 1 has been replaced by a pilot lamp. The pilot lamp radiation is reflected by a concave mirror 17 onto a condenser 20, beyond which is positioned a heat-absorbing filter 19. The pilot lamp radiation passing through the heat-absorbing filter 19 passes by way of a field stop 21 to the path-folding mirror 9 and the field lens 8, and is reflected by the selective mirror 3 in the direction of the test object 1.

In so doing, the selective mirror 3 prevents pilot lamp radiation, to which the radiation detector 5 is sensitive, from reaching said radiation detector 5. The use of a pilot lamp in a constant light pryometer according to the invention enables dark, non-glowing test objects 1 to be lit up and thus sighted.

In Fig. 3, the sighting device, consisting of an erecting lens 10, filter 11, field stop 12, graticule 13 and eyepiece 14, is disposed behind the selective mirror 3 in the direction of transmission.

In this case, the selective mirror 3 is formed in such a way that the sample radiation to be measured is reflected on to the field stop 4 and the radiation detector 5, and the visible radiation portion passes through the selective mirror 3. The collecting optics 2 thus images the test object 1 through the selective mirror 3 into the sighting device.

The spectral transmission or reflection curve shown in Fig. 4 is a result of the application of an alternating layer system 16 as described in Fig. 1. It can be seen from this curve that the infrared sample radiation to be measured is allowed to pass by the selective mirror 3 and a portion of the arriving visible radiation is reflected. The portion allowed to pass by the selective mirror 3, which has a wave number > 20,000 cm-', is not detected by the radiation detector 5 as it is not sensitive to this wave number.

Claims

1. A constant light pyrometer, comprising collecting optics, a radiation detector connected to an information processing unit, with or without a temperature indicator, a sighting device, and a selective mirror disposed obliquely in the beam path between the collecting optics and the radiation detector, the heat radiation focussed by the collecting optics being arranged to be spectrally divided in such a way by the selective mirror that the sample radiation in the infrared spectral range to be measured reaches the radiation detector, and at least a portion of the visible radiation from the sample reaches the sighting device.

2. A constant light pyrometer as claimed in claim 1, wherein the selective mirror comprises an infrared interference filter.

3. A constant light pyrometer as claimed in claim 1, wherein the selective mirror comprises a holder on which one or more optical layers are coated on one or both sides.

4. A constant light pyrometer as claimed in claim 1, wherein a field stop is disposed between the selective mirror and the radiation detector.

5. A constant light pyrometer as claimed in claim 3, wherein the holder for the selective mirror is coated with an alternating layer system consisting of Si 02 and Ti O2 in the layer combination H/2 (LHLHLHLHL) H/2.

6. A constant light pyrometer as claimed in any of claims 2 to 4, wherein the sighting device, which comprises a field lens, a pathfolding mirror, an erecting lens, a filter, a field stop, a graticule and an eyepiece, disposed one after the other and in this order in the beam path, is located in the direction of reflection to the selective mirror, and the radiation detector is located in the direction of transmission to the selective mirror.

7. A constant light pyrometer as claimed in any of claims 2 to 4, wherein the sighting device, which comprises an erecting lens, a filter, a field stop, a graticule and an eyepiece, disposed one after the other and in this order in the beam path, is located in the direction of transmission to the selective mirror, and the radiation detector is located in the direction of reflection to the selective mirror.

8. A constant light pyrometer as claimed in any of claims 2 to 4, wherein a field lens, a path-folding mirror, a field stop, a heat-absorbing filter, a condenser, a lamp and a concave mirror are disposed one after the other in the beam path in the direction of reflection to the selective mirror, such that the measur ing field is visible on the test object.

9. A constant light pyrometer substantially as hereinbefore described with reference to and as illustrated in the accompanying draw ings.