GB2159272A

GB2159272A - Optical pyrometer

Info

Publication number: GB2159272A
Application number: GB08511479A
Authority: GB
Inventors: Hans-Heinrich Ettwig
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1984-05-21
Filing date: 1985-05-07
Publication date: 1985-11-27
Also published as: DE3419244A1; IT1183539B; BE902395A; FR2564584A1; JPS60250222A; IT8520170A0; GB8511479D0

Abstract

The pyrometer can be moved angularly about its pivot axis by up to 20 DEG in both directions of movement (for one or more cycles of movement) from a so-called average observation angle in order to obtain readings which are investigated (after the optical signals have been converted into temperatures) for the purpose of establishing a minimum value. The pyrometer arrangement includes a swivel device, a polarisation filter which is equipped with a display and/or control device, and a minimum value storage unit. <IMAGE>

Description

SPECIFICATION Optical pyrometer This invention relates to an optical pyrometer.

The temperature of a product which is positioned in a furnace and is heated above 600"C is frequently determined by means of an optical pyrometer. A product, which is so positioned in order to be heated and kept warm, not only reflects characteristic radiation on the basis of its emissivity but also reflects the radiation of the furnace, in particular of the brickwork and also of the flames. Hence, pyrometers, which measure the sum of the characteristic radiation and reflective radiation, are usually used and the obtained result is converted; the resultant reading is inaccurate, and it is particularly inaccurate if the temperature of the furnace lies above that of the product at an unknown level and the radiation of the furnace is consequently very much greater than that of the product.The radiation of the furnace, which is reflected by the product, then falsifies the temperature measurement super portionally.

The principal aim of the invention is to improve the result of a temperature measurement with optical pyrometers on a product, which is positioned in a hot furnace, in solid phase in the temperature range above 600"C.

Accordingly, the present invention consists in an optical pyrometer receiver, into whose light path, which is directed to the product at a suitable observation angle, at the input end, is inserted a polarisation filter which serves for the parallel polarisation of the incident light; said receiver being arranged on a swivel device which allows adjustment of an average observation angle and periodic swivelling by up to 20 in both directions about said average observation angle; said filter being equipped with a display and/or control unit for determining the temperature of a product which is in the solid phase and whch has been heated to above 600"C and which is positioned in a warm furnace; and a minimum value storage unit; whereby the optical signal is converted into a temperature whose value is stored in said storage unit for investigation during at least one swivelling cycle in order to establish a minimum value. The observation angle may be approximately 70 in the case of a metallic product, whereas it may be approximately 57 in the case of an oxydic product.

In the case of a metallic product, the observation wave length may be smaller than or equal to 700 nm, whereas, in the case of an axydic product, the observation wave length may be smaller than or equal to 1000 nm.

One embodiment of an optical pyrometer according to the present invention is illustrated in the accompanying drawings and is given purely by way of example. In said drawings, Figure 1 is a diagrammatic representation of of part of a furnace in which a heated object is being scanned by a swivelled pyrometer; Figure 2 illustrates diagrammatically but in slightly more detail the swivelled pyrometer; and Figure 3 is a block diagram representing the complete information-gathering unit, including a display/output unit.

The optical pyrometer according to the present invention utilizes the knowledge that the reflectivity for radiation, which is polarized in parallel, changes in dependence upon the observation angle with respect to the normal onto the surface of the product in such a manner that it virtually becomes zero during observation at the so-called main angle of incidence. The temperature of the black body, which is a very accurate measure for the true temperature of the hot product, is measured by the pyrometer in the light, which is polarized in parallel, at the main angle of incidence; this main angle of incidence is a material-dependent optical constant which amounts to approximately 70 for a metallic product (e.g. carbon steel in the solid phase) and approximately 57 for an oxydic product (e.g. glasses and ceramics).In the case of a metallic product, this statement applies to the visible light and, in the case of an oxydic product, for wave lengths up to 1000 nm. The main angle of incidence need not be accurately known for the measurement and does not have to be determined in another manner. In fact, an average observation angle like the probable main angle of incidence is adjusted at the pyrometer. A swivel device of the pyrometer is then to be swivelled about the probable main angle of incidence by up to 20 in both directions. Since, as a result of the increased environmental temperature, the measured temperature can only be higher than the true temperature if the observation angle differs from the main angle of incidence, the displayed minimum is to be determined, to be stored and to be read during the swivelling operation.

Referring to Fig. 1, there is diagrammatically illustrated therein an arrangement in which a measuring aperture has been made in the wall of a heating furnace 1 in such a manner that a steel slab 2 can be observed from a pyrometer 3 at an angle of approximately 70 in relation to the vertical. Depending upon the required time resolution, by means of a frequency which is smaller than 5Hz, the pyrometer 3 is periodically swivelled about its horizontal axis at right angles to the optical axis in order that the observation angle be thereby periodically varied. The observed minimal temperature is detected by the minimum value store and stored and subsequently displayed as a measured quantity.

Referring to Fig. 2, the observation angle of approximately 70 is indicated by the refer ence numeral 7. The pyrometer 3, with a series-connected optical polarisation filter 4, is mounted on a pivot device 5 at the angle 7.

Depending upon the required time resolution the pyrometer 3 is pivoted with the above mentioned frequency about the pivot axis 6 at right angles to the optical axis, (for example, periodically by i 5 ) so that the observation angle is thereby periodically varied, following said example, between 65 and 75 .

Referring to Fig. 3, this movement is controlled by a control unit 8. The optical signal, which is converted into a temperature in a measuring converter 9, is stored in a minimum value store 10 and is investigated to establish a minimum value over one or more than one movement cycle. This minimum value is transferred as measured true temperature to a measured value display and output unit 11.

A numerical example will serve to explain the operating capacity of the proposed measuring device. Thus, a scaled steel ingot whose emissivity amounts to 0.8 and which has a true temperature of TB = 1 050 C is positioned in a heating furnace which has an inner temperature of To = 1 150'C. During vertical or nearly vertical observation, an optical pyrometer supplies a measured value for the ingot temperature of 1099"C if an emissivity of 0.8 is adjusted, and a value of 1080"C if an emissivity of 1.0 is adjusted. The proposed measuring device allows 1056"C to be obtained for an observation angle of 60', 1068"C for 80 and 1051 C for the main angle of incidence.

Claims

1. An optical pyrometer receiver, into whose light path, which is directed to the product at a suitable observation angle, at the input end, is inserted a polarisation filter which serves for the parallel polarisation of the incident light; said receiver being arranged on a swivel device which allows adjustment of an average observation angle and periodic swivelling by up to 20 in both directions about said average observation angle; said filter being equipped with a display and/or control unit for determining the temperature of a product which is in the solid phase and which has been heated to above 600"C and which is positioned in a warm furnace; and a minimum value storage unit; whereby the optical signal is converted into a temperature whose value is stored in said storage unit for investigation during at least one swivelling cycle in order to establish a minimum value.

2. A receiver as claimed in Claim 1, wherein the observation angle is approximately 704 in the case of a metallic product.

3. A receiver as claimed in Claim 1, wherein the observation angle is approximately 57'in the case of an oxydic product.

4. A receiver as claimed in Claim 2, wherein the observation wave length is smaller than or equals 700 nm.

5. A receiver as claimed in Claim 3, wherein the observation wave length is smaller than or equals 1000 nm.

6. An optical pyrometer constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

7. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.