GB2068109A - Monitoring strip temperature - Google Patents

Abstract

A system for monitoring the temperature of a strip comprises a scanning photodiode array illuminated by an image of the strip, and a computation means, in particular a microprocessor having a memory in which one or more look-up tables are stored, for converting the signals from each photodiode of the array into a measurement of the temperature at a corresponding point on the surface of the strip.

Description

SPECIFICATION Improvements in temperature monitoring The present invention relates in general to temperature monitoring and is particularly intended for measuring the temperature of a hot slab in a rolling mill.

In rolling mills and in particular when rolling steel, uneven water cooling of the rollers leads to an uneven distribution of temperature across the width of a strip being rolled and this can cause changes in the metallurgical structure of the material causing surface marks. More seriously, when the steel is cold or has local cold spots prior to entry into the finishing rollers, extra work is required from the rollers in order to squeeze the material and this can cause the safe-load setting on the rolls to be exceeded, resulting in "a cobble" as it is known in the trade. Such a cobble effectively results in the mill being stopped for approximately two hours to enable normal working conditions to be reestablished and even in the best regulated of mills this can happen once or twice a week.

It would therefore be advantageous to monitor the temperature of a strip being rolled in orderto minimise the possibility of the safe-load setting on the rolls being exceeded and thereby minimising expensive down periods.

In accordance with the present invention, there is provided a system for monitoring the temperature of a strip, which comprises a scanning photodiode array illuminated by an image of the strip and means connected to the photodiode array for converting the signal from each photodiode of the array into a measurement of the temperature at a corresponding point on the surface of the strip.

The invention is predicated upon the fact that the amount of energy emitted in the spectral range from 700 to 1100 nanometres is dependent upon the temperature of the strip and also upon the material of which it is made. The material affects the emissivity, that is to say the proportion of radiation emitted as against the amount that would be emitted by a perfect black body radiator which, by definition, has an emissivity of 1. The emissivity of steel is typically 0.85 at a temperature of 800"C, but this factor is itself a function of temperature and also of the carbon content of the steel.

It is conceivable in respect of a mill operating always with the same type of steel within the same temperature range to provide a single function generator to convert the output signals from the photodiodes into signals exclusively dependent upon temperature. In practice, however, any given mill will at different times operate with different steels and also at widely different temperatures.

Although the range of acute interest is from 700 to 1 200 C, the use of photodiode array cameras is in principle capable of making measurements of temperature within the much wider range from 600O to 8000"C.

To cope with a wide range of materials, the conversion of the output signals of the photodiode into temperature measurement signals may conveniently be effected by a memory of a microcomputer in which are stored, in the form of a look-up table, the emissivities of the different steels at different temperatures as obtained by exact measurement during a calibration.

To cope with a wide range oftemperatures, it is possible to alter the integration time, that is to say the time during which the photodiode array is exposed to the emitted radiation during each scan.

When provision is made for varying the integration time, more than one table of calibration information will have to be stored. For example, the integration period or exposure time may be selected from 1, 2, 4, 8, 16 and 32 milliseconds with automatic switching from the output of a camera peak detector such as to maintain the output of the camera at between 25% and 75% of the maximum saturated output. For each of these integration times, there will be a corresponding look-up table holding array characterisation information.

Because the photodiode response on an element by element basis is not absolutely uniform there may typically be errors of a maximum of 3% caused by this element to element variation. The provision of a micro-computer may conveniently be used to eliminate this source of error by the use of a look-up table. To achieve this, the output at, say, 50% saturation in terms of the uniformity of response may be normalised by the use of a memorised further multiplication factor.

1. A system for monitoring the temperature of a strip, which comprises a scanning photodiode array illuminated by an image of the strip and means connected to the photodiode array for converting the signal from each photodiode of the array into a measurement of the temperature at a corresponding point on the surface of the strip.

2. A system as claimed in Claim 1, wherein the means for converting comprises a microprocessor having a memory in which there is stored a look-up table enabling the intensity of the radiation emitted from the strip to be converted into a meausrement of the actual temperature.

3. A system as claimed in Claim 1 or Claim 2, wherein the memory incorporates a plurality of look-up tables, each corresponding to a respective integration period of the photodiodes of the photodiode array.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in temperature monitoring The present invention relates in general to temperature monitoring and is particularly intended for measuring the temperature of a hot slab in a rolling mill. In rolling mills and in particular when rolling steel, uneven water cooling of the rollers leads to an uneven distribution of temperature across the width of a strip being rolled and this can cause changes in the metallurgical structure of the material causing surface marks. More seriously, when the steel is cold or has local cold spots prior to entry into the finishing rollers, extra work is required from the rollers in order to squeeze the material and this can cause the safe-load setting on the rolls to be exceeded, resulting in "a cobble" as it is known in the trade. Such a cobble effectively results in the mill being stopped for approximately two hours to enable normal working conditions to be reestablished and even in the best regulated of mills this can happen once or twice a week. It would therefore be advantageous to monitor the temperature of a strip being rolled in orderto minimise the possibility of the safe-load setting on the rolls being exceeded and thereby minimising expensive down periods. In accordance with the present invention, there is provided a system for monitoring the temperature of a strip, which comprises a scanning photodiode array illuminated by an image of the strip and means connected to the photodiode array for converting the signal from each photodiode of the array into a measurement of the temperature at a corresponding point on the surface of the strip. The invention is predicated upon the fact that the amount of energy emitted in the spectral range from 700 to 1100 nanometres is dependent upon the temperature of the strip and also upon the material of which it is made. The material affects the emissivity, that is to say the proportion of radiation emitted as against the amount that would be emitted by a perfect black body radiator which, by definition, has an emissivity of 1. The emissivity of steel is typically 0.85 at a temperature of 800"C, but this factor is itself a function of temperature and also of the carbon content of the steel. It is conceivable in respect of a mill operating always with the same type of steel within the same temperature range to provide a single function generator to convert the output signals from the photodiodes into signals exclusively dependent upon temperature. In practice, however, any given mill will at different times operate with different steels and also at widely different temperatures. Although the range of acute interest is from 700 to 1 200 C, the use of photodiode array cameras is in principle capable of making measurements of temperature within the much wider range from 600O to 8000"C. To cope with a wide range of materials, the conversion of the output signals of the photodiode into temperature measurement signals may conveniently be effected by a memory of a microcomputer in which are stored, in the form of a look-up table, the emissivities of the different steels at different temperatures as obtained by exact measurement during a calibration. To cope with a wide range oftemperatures, it is possible to alter the integration time, that is to say the time during which the photodiode array is exposed to the emitted radiation during each scan. When provision is made for varying the integration time, more than one table of calibration information will have to be stored. For example, the integration period or exposure time may be selected from 1, 2, 4, 8, 16 and 32 milliseconds with automatic switching from the output of a camera peak detector such as to maintain the output of the camera at between 25% and 75% of the maximum saturated output. For each of these integration times, there will be a corresponding look-up table holding array characterisation information. Because the photodiode response on an element by element basis is not absolutely uniform there may typically be errors of a maximum of 3% caused by this element to element variation. The provision of a micro-computer may conveniently be used to eliminate this source of error by the use of a look-up table. To achieve this, the output at, say, 50% saturation in terms of the uniformity of response may be normalised by the use of a memorised further multiplication factor. CLAIMS

1. A system for monitoring the temperature of a strip, which comprises a scanning photodiode array illuminated by an image of the strip and means connected to the photodiode array for converting the signal from each photodiode of the array into a measurement of the temperature at a corresponding point on the surface of the strip.

2. A system as claimed in Claim 1, wherein the means for converting comprises a microprocessor having a memory in which there is stored a look-up table enabling the intensity of the radiation emitted from the strip to be converted into a meausrement of the actual temperature.

3. A system as claimed in Claim 1 or Claim 2, wherein the memory incorporates a plurality of look-up tables, each corresponding to a respective integration period of the photodiodes of the photodiode array.