JPS6049851B2 - Calibration method for steel plate surface temperature - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for calibrating the surface temperature of a steel plate measured with a thermocouple.

Thermocouples are widely used to measure the surface temperature of steel plates.

Temperature measurement using a thermocouple is of course a contact type, and non-contact types such as radiation thermometry are preferred for temperature measurement on the surface of a moving steel plate, but thermocouples are usually used to calibrate radiation thermometers. . By the way, the surface temperature of the heated steel plate measured by such a thermocouple is lower than the true temperature, and if the radiation thermometer is calibrated using the measured temperature, an incorrect calibration will be performed. The reason why the steel plate surface temperature measurement result using a thermocouple shows a value lower than the true temperature is thought to be the loss of heat from the steel plate surface to the thermocouple thermometer, but non-contact temperature measurement is preferable to avoid this.

An object at temperature T has radiant energy E, =EEb(T)
, so if we measure this and use the Wien formula Eb(T)=C, λ-゜exp(-Co/λ・T), we can find the object temperature T, which is the principle of radiation thermometry. However, there is a problem in that the emissivity ε of the surface of the temperature-measuring object is generally unknown. This unknown emissivity E is calculated using a blackbody furnace, and the radiant energy E from the surface of the object to be measured is
The sum E of the radiant energy reflected by the radiant energy from the blackbody furnace applied to the surface of the object and the radiant energy E. The present inventors have developed a method in which ε is determined by measuring ε, and then the temperature T of the object is determined, but strictly speaking, even with this method, the radiant energy from the blackbody furnace does not reach the surface of the object. There is a problem in that the diffuse reflection coefficient representing the rate of reflection is unknown (therefore, an estimated value is used). The present invention can remove emissivity ε through appropriate operations and measure Eb(T),
This proposes a method that can determine the true temperature T and calibrate the thermocouple temperature value.

According to this method, the above-mentioned diffuse reflection coefficient can also be measured at the same time. Next, this will be explained with reference to examples. In FIG. 1, 10 is an object to be measured, specifically a heated steel plate, 12 is a radiometer, 14 is a reflector, 16 is a rotating sector, and 18 and 20 are transmission windows provided in the radiation passage of the furnace wall 22. (filter). These members 14, 16, 18 and 20, 12 are arranged at equal angles with respect to the normal N to the temperature measuring point 0, that is, on the path of specularly reflected incident light and reflected light. 24 is a thermocouple installed near temperature measurement point 0, 26
There is a heater.

In this temperature measurement system, the radiant energy emitted from the steel plate 10 passes through the filter 20, enters the radiometer 12, passes through the filter 18, enters the reflector 14, and is reflected and returns along the same path. and enters the radiometer 12 via the filter 20.

These radiant energy paths 11 and 12 are in a specular reflection relationship, that is, the angles θ with respect to the normal N are equal. Since radiant energy has the same characteristics as light in terms of reflection, radiometer 1
The only radiant energy that enters 2 is through the passages 11 and 12, which is effective for noise shielding. That is, the furnace wall 22
If the temperature is high, it will emit radiant energy that cannot be ignored, and there is a risk that this will be reflected by the steel plate 10 and enter the radiometer 12. Therefore, the temperature should be kept sufficiently low compared to the steel plate to be measured so that the radiant energy from the furnace wall can be ignored. Keep it. Of course, since the radiant energy emitted by the reflecting mirror 14 can be received by the radiometer 12, the reflecting mirror 14 should also be kept at a sufficiently low temperature so that the radiant energy beyond that point can be ignored. The rotating sector 16 has a portion that allows radiant energy to pass through, such as an opening, and a portion that does not allow the radiant energy to pass through. For example, the radiant energy-absorbing surfaces are rotated so that they alternately lie on the passageway 12. This rotating sector is also kept sufficiently cool that it does not itself emit radiant energy. ) measurement system, the true temperature of the steel plate surface! T, emissivity is E, diffuse reflection coefficient is P1, reflectance of reflector 14 is Ral filter 1
The following equation holds true, where γ is the transmittance of 8 and 20, E1 is the received light energy of the radiometer 12 when the rotating sector 16 closes the optical path, and E2 is the transmission when the optical path is opened.

The unknowns in equations (1) and (2) are E, Eb(T), and p, so equations (1) and (2) cannot be solved at this point.

Now, if we let the difference between the two equations be ΔE, we get this (
If the temperature T is constant, the equation 3) becomes maximum at E1=τ·Eb(T)/2. The values of El and ΔE at this time are
If ΔE*, then the following equation is obtained from these equations (4) and (5). Using Equation (6), Eb(T) can be determined from E*1,τ, and the steel plate surface temperature T can be determined. Also, using equation (7), ΔE*, E rest, τ,
The diffuse reflection coefficient p can be determined from Ra. The maximum value of ΔE can be achieved relatively easily.

In other words, if the atmosphere around the steel plate is made reducing, the cold rolled steel plate will maintain its mirror surface, but if the atmosphere is then changed to an oxidizing atmosphere, the surface of the steel plate will oxidize and bluish (become blue), with an emissivity of 0. It varies from about .25 to 0.85. Along with this, the received light energies El and E2 of the radiometer change as shown in FIG. If the atmosphere in the furnace is changed from reducing to oxidizing at an appropriate speed, and during this time the rotary sector 16 is rotated to obtain a large number of El and E2 and plot them, Figure 2 is drawn, from which ΔE=E2 The maximum value of the upper one is easily found.
This maximum value occurs when ε=0.5. That is, the aforementioned Δ
The condition E1=τ・Eb(T)/2 that maximizes E is (1
) As is clear from the equation, E=0.5. If a large number of measured values are obtained, the maximum value of ΔE can be obtained fairly accurately from the graph of FIG. 2, but it is also possible to use a relatively small number of measured values and obtain the maximum value through arithmetic processing.

FIG. 3 replaces FIG. 2 with the relationship of E1-ΔE to clearly show the change in ΔE.

During this measurement, it is necessary to keep the steel plate temperature constant, and this can be accomplished by controlling the energization of the heater 26 so that the temperature Ta indicated by the thermocouple is used as an index and becomes constant. Incidentally, although the temperature Ta is not the true temperature, this does not pose any problem in controlling the steel plate temperature to be constant. FIG. 4 shows the procedure for determining T from Eb(T) determined by equation (7).

This can be done by solving the above formula, but it is complicated, so
Generally, an E(b)-T curve C1 is created in advance, and the true temperature T is determined from this. Figure 5 shows the calibration procedure.

The measurement of the true temperature T described above is carried out in various ways while changing the steel plate temperature, and a Ta-T curve C2 is obtained. If Ta=T, this curve C2 becomes a 452 diagonal line C3, but generally the curve C
2 is above diagonal line C3. That is, T>Ta. This curve C2 is a calibration curve to be determined, and using this curve, the true temperature T is determined from the thermocouple temperature value Ta. Thermocouples thus calibrated are also used to calibrate radiometers in real reactors. However, this calibration curve is based on the thickness of the steel plate (heat capacity).
Since it may change depending on the steel plate, prepare several types of calibration curves to match the target steel plate. As explained above, according to the present invention, it is possible to accurately measure the copper plate surface temperature by radiation without being affected by emissivity, diffuse reflection coefficient, etc., and thereby calibrate the indicated value of the thermocouple and The advantage is that accurate steel sheet surface temperature measurement is possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention, and FIGS. 2 to 5 are graphs showing relationships between various variables.

Claims (1)

[Claims] 1. A radiometer and a reflector are arranged on a heated steel plate so that the radiant energy emitted from the steel plate is directly incident on the radiometer after being specularly reflected on the reflector and the object surface, and the direct incident energy is incident on the radiometer. radiant energy E_1 and the sum E_2 of the radiant energy incident after reflection and the radiant energy E_1.
is measured, the emissivity of the surface of the steel plate is changed while the temperature of the steel plate is kept constant, the radiant energy E_1 is determined when the difference ΔE=E_2−E_1 becomes the maximum, and the value E_1* and the black body radiant energy are calculated. The surface temperature T of the steel plate is determined using the relational expression Eb(T)=2/γ−E_1*, and the indicated temperature Ta is obtained by installing a thermocouple near the temperature measuring part of the steel plate, and the temperature T
A method for calibrating a steel plate surface temperature measured with a thermocouple, the method comprising calibrating a at the temperature T.