JPS5987330A - Temperature measuring method of eddy current type - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measurement method using a globe-type eddy current detection coil, and the present invention relates to a temperature measurement method using a globe-type eddy current detection coil. The present invention relates to a method for measuring temperature near a surface.

For example, in hot rolling operations, the temperature at and near the surface of a rolling roll has a great effect on the quality of the rolled product and the life of the roll itself, so monitoring temperature changes is extremely important for rolling operation management. be. During rolling with a force of 1, the rolls are rotating at high speed, so it is not possible to measure the temperature by directly contacting the temperature sensing element with the rolls, and there is also a water film caused by cooling water and water vapor. Since the atmosphere is full, it is difficult to obtain the desired measurement accuracy even if a radiation thermometer is used. There is also a temperature measurement method that uses an eddy current thermometer, but with conventional eddy current thermometers, the measurement temperature range is limited to low temperature areas, and the surface temperature of the roll during hot rolling is around 600°C. This method was not applicable to objects that rise up to 300 degrees Celsius because changes in output due to changes in magnetic permeability of the object to be measured would be complicated.

The present invention provides a temperature measurement method that non-contactly measures the temperature at and near the surface of an object such as a mill roll over a wide temperature range in an atmosphere where a water film exists and is filled with water vapor.

The present invention will be explained in detail below.

Since the electrical and magnetic properties of magnetic materials such as rolling rolls, such as magnetic permeability and conductivity, change depending on temperature, a high-frequency excitation current was passed through the primary coil of the detection coil installed close to the surface of the object to be measured. In this case, the eddy current generated near the surface of the object to be measured changes depending on the temperature change of the object to be measured. Changes in this eddy current appear as changes in the output voltage of the secondary coil placed coaxially inside the primary coil, and changes in the temperature of the object to be measured can be measured by changes in this output voltage. .

Now, in the detection coil configuration in which the primary coil 1 and the secondary coil 2 are arranged coaxially as shown in Fig. 1, it is assumed that the coil size, shape, number of turns, current, and thickness of the object to be measured are constant. : When the voltage induced in the secondary coil 2 is
Magnetic permeability μ of the object to be measured S.

It is determined by the conductivity σ, the distance d between the object to be measured and the detection coil (hereinafter referred to as lift-off), and the frequency f of the excitation current flowing through the primary coil 1. Here, the two-arrow coil induced voltage V2
is shown on the complex voltage plane as follows.

(2) For a combination of constant values of magnetic permeability μ, conductivity σ, and lift-off d1 frequency f, one value of induced voltage v2 is determined, and this value is represented by one point A in the complex voltage plane. That is, V2=func, (μ, a, d, f) ---
---It is expressed as (1).

■ When either or both of conductivity σ and frequency f changes, point AJ draws a certain curve. If this is a curve Cn, then the product of the point AH conductivity σ and the frequency f (σx
When f) increases (decreases), it rotates clockwise on the curve Cn (
counterclockwise) VC moves.

That is, V2 = func, (σX f, μ, d)
−−−−−=−(2) 3−.

This is illustrated in Figure 2. In FIG. 2, the horizontal axis is the real component of the induced voltage 2, and the vertical axis is the imaginary component of the induced voltage v2. However, here, the real part VRe and imaginary part VIm of the induced voltage (2) are normalized by the absolute value of the induced voltage Vo when there is no object to be measured.

In the figure, when the point Aij, (σxf) corresponding to a certain combination of μ, σ, d, and f increases (decreases), it moves clockwise (counterclockwise) on the curve Cn.

■ As magnetic permeability μ increases (decreases), curve C in Figure 2
n changes in the direction of curve CM (curve Co) in the figure. Here, the curve Co(qThe object to be measured is a non-magnetic material, that is, the magnetic permeability μ is μm.
This is the curve for the case. The curve swells upward from CO as the magnetic permeability μ becomes steeper, but the bulge of the curve saturates to a certain size and gradually approaches the curve shown as CM in the figure, and the magnetic permeability μ increases as the size of the detection coil increases. When the magnetic permeability exceeds a certain value (this is assumed to be μm) determined by ) ---
---・-・(3) 1 μ≧μm) In the above, the value μ=μm of the magnetic permeability μ at which the upward bulge of the curve is saturated becomes smaller (larger) as the thickness of the object to be measured becomes larger (smaller).

Furthermore, when the frequency f exceeds a certain frequency value (this is defined as fm) determined by the dimensions of the detection coil,
Whether the magnetic permeability μ is larger or smaller than μm, the point Aid curve CM (including the curve Cn) becomes like this. That is, V2 = func, (i], d)...
...-14) Provided that f≧fm) ■ When lift-off d is increased, point A moves toward point B on the scale of 1.0 on the vertical axis in FIG.

The present invention was created based on the knowledge about the behavior of the induced voltage v2 on the complex voltage plane as described above.

From the above, if temperature is measured under conditions such that point A indicating the induced voltage (2) on the complex voltage plane moves on the car 10M, temperature can be measured over a wide temperature range with the same detection coil. I understand that. One such condition is that the frequency f is equal to fm regardless of the temperature range.
It is conceivable to set the frequency above above so that the point A is at the bottom of the curve CM or Cn, but in low temperature regions, increasing the frequency f will reduce the temperature measurement sensitivity compared to the conventional method. Undesirable. Therefore, in the present invention,
The magnetic permeability μ of the object to be measured is the induced voltage v2 on the complex voltage plane.
In the temperature range below this boundary temperature (hereinafter referred to as low temperature range), the induced temperature is as shown in Fig. Set the point X where the real component is almost the maximum on the car 10M, and set the frequency fx corresponding to this point XVc as the reference excitation frequency, and the induced voltage ■2 during temperature measurement.
The frequency is variably controlled so that the value always corresponds to point The frequency fx' (≧fm) corresponding to point X' is set as the reference excitation frequency, and the frequency is variably controlled so that the induced voltage (2) always has a value corresponding to point X' during temperature measurement. By doing this, changes in the temperature of the object to be measured can be understood as changes in the excitation frequency.

In the above, the boundary between the low temperature region and the high temperature region is the temperature at which the magnetic permeability μ of the object to be measured is equal to the aforementioned μm, so
This boundary temperature varies depending on the material (component) and thickness of the object to be measured and the dimensions of the detection coil.

FIG. 4 shows a circuit configuration of a device in an embodiment of the present invention. High-frequency oscillators 6 and 7 for generating a high-frequency voltage at a reference excitation frequency (18D) change the phase of this high-frequency voltage waveform to a predetermined phase difference ψ1. It is a phase shifter that shifts by ψ2. 20' is a detection coil, and the output of the high-frequency oscillator 18 is applied to the primary coil 1 which is added to the detection coil. This primary coil 1 is the first
As shown in the figure, it is installed close to the object to be measured.
A coaxial secondary coil 2 is installed inside the coil. 2
The output of the next coil 2 is inputted to a synchronous detector 4 via an amplifier 3. The phase shift angle ψ of the phase shifter 6 is determined by the direction of the change vector of the induced voltage 2 due to the change in lift-off d at the point X or point X' on the complex voltage plane in FIG. 3 and the curve CM.
The angle corresponds to the angle formed by the synchronous detector 4.
The output is the change in induced voltage (2) due to lift-off d. When the position of point X or point X' on the complex voltage plane in FIG. 3 is set, the phase angle of point X or point A phase shift angle ψ2 is set. The output of the phase shifter 7 is used to detect the induced voltage v2 with a synchronous detector 8, and a 90° phase shifter 10 is used to detect the induced voltage v2.
It can also be added to The output of the 90° phase shifter 10 is detected by the synchronous detector 11 against the induced voltage v2. In other words, the output of the synchronous detector 8 is the 92 phase component v2ψ2 of the induced voltage v2.
, the induced voltage v2 (ψ2
190°) phase component ■2 (ψ2+90°), so by calculating tan −' in the phase difference calculator 13, the output is the deviation of the phase angle of the induced voltage v2 from the reference phase angle ψ2, That is, point X or l"lX in Figure 3
'y+> is expressed as a phase angle. The output of the phase difference calculator 13 is added to the lift-off fluctuation correction calculator 14 together with the output of the integrator 5, so that the output of the integrator 5 becomes 0.
If not, the induced voltage due to change in lift-off d■
After the change in 2 is removed, the frequency converter 1
5, and the change Δf in the frequency of the primary coil excitation current necessary to make the output of the phase difference calculator 13 0Vr-
and is added to the frequency-temperature conversion calculator 16 and the oscillation frequency control circuit 17.
Then, the oscillator constant is changed so that the frequency of the high-frequency oscillator 18 is changed by Δf'. In the frequency-temperature conversion calculator 16, the frequency change Δf is as follows: Ko11fo=μ/σ Ko・(fo+Δf)−μ/σ+Δ(μ/σ)...
・・・・・・From (5), Δ(μ/σ)=Ko・(fo+Δf]−μ/σ=Ko・
(fo-+-af)-Ko@f.

=Ko・Δf 0. ,,−,−
It is converted into Δ(μ/σ) using the relationship (6) and output as a temperature change. Here, the value of 1μ/σ×f at the Koid point X or point X' is the frequency of the high frequency oscillator 18 at the current moment.

In this way, changes in the induced voltage in the secondary coil due to changes in the temperature of the object to be measured are detected as a deviation from the current frequency, so it is possible to In addition, by setting in advance the points on the complex voltage plane and the corresponding excitation frequencies, it becomes possible to measure temperature with high accuracy over a wide temperature range.

An example in which the present invention is applied to temperature measurement of a work roll for hot rolling will be shown below. The configuration of the detection coil used was: Primary coil inner radius: 25 x 10-10-3 (Next coil outer radius: 30 x 10''-3 [rn]22nd coil inner radius: 1ox1o'lm, l1 Secondary coil outer radius : 15 x 10'-3 [I11] Coil length: 10 x IF' [m] Number of primary coil turns: 40 [L'urn] Number of turns of secondary coil:
1O (1 [Tu port]) Primary current: 0
．． 25 [Al, and the values of μm and fm in this case are μm Ki 120X4 π X10-7 [T! /ir+)fm: 115 [: KHz]. With the above coil configuration, the work roll temperature range is 20
For ~300℃, set the standard excitation frequency to 50Kl-■z
For the temperature range of 300°C to 600°C, the reference excitation frequency was set to 175 [KHz], and as a result, measurement was possible with sufficient accuracy and f:.

As described above, according to the present invention, the temperature at and near the surface of a magnetic material such as a rolling roll, which has a thickness larger than the dimensions of the detection coil, can be measured non-contact and with high accuracy over a wide temperature range'i)). Even if there is an oil film, water film, etc. on the surface of the object to be measured, or even if the object is moving at high speed, it is not affected and stable temperature measurement is possible. This expands the possibility of temperature measurement in areas where it has been difficult to measure temperature in the past.

[Brief explanation of drawings]

Fig. 1 is a front view showing the configuration of the eddy current detection coil, Fig. 2 is a chart for explaining the behavior of the secondary coil induced voltage on a complex voltage plane, and Fig. 3 is a diagram showing the behavior of the secondary coil induced voltage in the present invention. FIG. 4 is a diagram for explaining the setting of a specific point on a complex voltage plane, and is a block diagram showing the circuit configuration of an apparatus in an embodiment of the present invention. 20: Detection coil, l: Primary coil, 2: Secondary coil, 4, 8, 1.1: Synchronous detector, 6, 7, 10: Phase shifter, 5, 9, 12: Integrator , 13: Phase shift difference calculator, 1
4: ') Foot-off fluctuation correction computing unit, 15: Frequency converter, 16: Frequency-to-temperature conversion computing unit, 17: Oscillation frequency side, control circuit, 18: High frequency oscillator, 19: Reference phase difference computing unit. Patent Applicant Agent Patent Attorney Ya Fuki Hagiyuki (and 1 others)
name) 12-

Claims (1)

[Claims] In a temperature measurement method using a globe-type eddy current detection coil in which a secondary coil is coaxially arranged inside a primary coil, when the secondary coil induced voltage is shown on a complex voltage plane, the induced voltage is expressed by the following parameter K: Under a specific range of the magnetic permeability of the object to be measured or the excitation frequency of the primary coil, which is the measurement condition determined at one point on the complex plane, the induced voltage is determined in advance at a specific point on the complex voltage plane. The excitation frequency of the primary coil is set to An eddy current temperature measurement method characterized by determining the amount of temperature change.