JPS6360332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measurement method using a probe-type eddy current detection coil, and in particular to a method for measuring temperature using a probe-type eddy current detection coil, and in particular, the surface of a magnetic material whose thickness is considered to be infinite with respect to the dimensions of the detection coil. It relates to a method of measuring nearby temperature.

For example, in hot rolling operations, the temperature at and near the surface of a rolling roll has a major impact on the quality of rolled products and the life of the roll itself, so knowing the temperature changes is extremely important for managing rolling operations. be. However, during rolling, the rolls are rotating at high speed, so it is not possible to measure the temperature by directly contacting the temperature sensor with the rolls, and furthermore, there is a water film caused by cooling water and the rolls are filled with water vapor. Even if a radiation thermometer is used, it is difficult to obtain the desired measurement accuracy. 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 rolls during hot rolling is limited.
For objects that heat up to around 600℃, changes in output due to changes in magnetic permeability of the object to be measured become complicated.
It was not applicable.

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 rolling roll in an atmosphere where a water film exists and is filled with water vapor over a wide temperature range. be.

The present invention will be explained in detail below.

Electrical and magnetic properties such as magnetic permeability and conductivity of magnetic materials such as rolling rolls change with temperature, so it is necessary to apply a high-frequency excitation current to the primary coil of a detection coil installed close to the surface of the object to be measured. If it flows,
Eddy currents generated near the surface of the object to be measured change depending on changes in the temperature of the object to be measured. Changes in this eddy current appear as changes in the output voltage of the secondary coil coaxially arranged inside the primary coil, and changes in the temperature of the object to be measured can be measured by changes in the output voltage. .

Now, primary coils 1 and 2 as shown in Fig.
In a detection coil configuration in which the secondary coil 2 is arranged coaxially, when the coil size, shape, number of turns, current, and thickness of the object to be measured are constant, the secondary coil 2
The voltage V ₂ induced in is the 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 2
The next coil induced voltage V ₂ is shown on the complex voltage plane as follows.

For a combination of fixed values of magnetic permeability μ, conductivity σ, liftoff d, and frequency f, the induced voltage V ₂
One value is determined, which is 1 in the complex voltage plane.
It is represented by point A. That is, it is expressed as V ₂ =func.(μ, σ, d, f) (1).

When either or both of conductivity σ and frequency f changes, point A draws a certain curve. Assuming that this is a curve Cn, the point A moves clockwise (counterclockwise) on the curve Cn as the product (σ×f) of conductivity σ and frequency f increases (decreases). That is, it is expressed as V ₂ =func.(σ×f, μ, d) (2).

This is illustrated in Figure 2. Second
In the figure, the horizontal axis is the real component of the induced voltage V ₂ , and the vertical axis is the imaginary component of the induced voltage V ₂ . However, here, the real part V _R e and the imaginary part V _I m of the induced voltage V ₂ are the induced voltage Vo when there is no object to be measured.
It is normalized by the absolute value of .

In the figure, point A corresponding to a certain combination of μ, σ, d, f rotates clockwise (counterclockwise) on curve Cn as (σ×f) increases (decreases).
move to.

When the magnetic permeability μ increases (decreases), the curve Cn in FIG. 2 changes in the direction of the curve C _M (curve Co) in the same diagram. Here, the curve Co indicates that the object to be measured is a non-magnetic material, that is, the magnetic permeability μ is μ=1.0×4π×10 ^-7
This is a curve for [H/m]. As the magnetic permeability μ increases, the curve swells upward from Co, but the bulge of the curve saturates to a certain size and gradually approaches the curve shown as C _M 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 (which is defined as _μm ) determined by do. That is, V ₂ =func.(μ/σ×f′d) (3) where (μ≧μm). In addition, in the above, the value of magnetic permeability μ at which the upward bulge of the curve is saturated μ = μm
becomes a smaller (larger) value as the thickness of the object to be measured becomes larger (smaller).

Furthermore, when the frequency f exceeds a certain frequency value determined by the dimensions of the detection coil (this is called fm), point A will curve C _M (curve Cn ) with K=μ/σ×f as a parameter. That is, V ₂ = func. (μ/σ×f′, d) …(4) However, (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 Figure 2. Move.

The present invention was created based on the knowledge about the behavior of the induced voltage V ₂ on the complex voltage plane as described above.

From the above, the induced voltage on the complex voltage plane
It can be seen that if the temperature is measured under conditions such that the point A indicating V ₂ moves on the curve C _M , it is possible to measure the temperature over a wide temperature range with the same detection coil. One such condition may be to set the frequency f to be higher than the above-mentioned fm regardless of the high order of the temperature range so that the point A is at the bottom of the curve C _M or Cn. In a low temperature region, increasing the frequency f is not preferable because the temperature measurement sensitivity will be lower than in the conventional method. Therefore, in the present invention, the temperature at which the magnetic permeability μ of the object to be measured becomes the same as μm at which the point A showing the induced voltage V ₂ on the complex voltage plane moves on the curve C _M is set as a boundary. In the temperature range below this boundary temperature (hereinafter referred to as the low temperature range), the induced voltage is as shown in Figure 3.
Set the point X where the point indicating V ₂ is almost the maximum of the real component on the curve C _M , and calculate the frequency corresponding to this point
fx is the reference excitation frequency, and the induced voltage V 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 V 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
Since this is the temperature at which the magnetic permeability μ of the object to be measured is equal to the aforementioned μm, 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. 18 is a high frequency oscillator for generating a high frequency voltage of a reference excitation frequency, and 6 and 7 are phase shifters for shifting the phase of this high frequency oscillation voltage waveform by a predetermined phase difference of ₁ and ₂ . 20 is a detection coil, and the output of the high frequency oscillator 18 is applied to the primary coil 1 of the detection coil 20. As shown in FIG. 1, this primary coil 1 is installed close to the object to be measured, and a coaxial secondary coil 2 is installed inside it. The output of the secondary coil 2 is input to a synchronous detector 4 via an amplifier 3. Phase shift angle ₁ of phase shifter 6
is the point X or the point on the complex voltage plane in Figure 3.
Induced voltage due to change in lift-off d at X′
This angle corresponds to the angle formed by the direction of the change vector of V ₂ and the curve _CM , and therefore the output of the synchronous detector 4 is the change due to the lift-off d of the induced voltage V ₂ . When the position of point X or point X' on the complex voltage plane in Fig. 3 is set, the reference phase difference calculator 1
At step 9, the phase angle of point X or point X' is calculated, and the phase shift angle ₂ of the transfer device 7 is set. The output of the phase shifter 7 is used by the synchronous detector 8 to detect the induced voltage V ₂ and is also applied to the 90° phase shifter 10 .
The output of the 90° phase shifter 10 is detected by a synchronous detector 11 against the induced voltage V ₂ . In other words, the output of the synchronous detector 8 is a _two -phase component V _{2 2} of the induced voltage V ₂ ,
The output of the synchronous detector 11 is the induced voltage V ₂ ( ₂ +90°)
Since the phase component is V ₂ ( ₂ +90°), by calculating tan ^-1 in the phase difference calculator 13, the output is the deviation of the phase angle of the induced voltage V ₂ from the reference phase angle ₂ , that is, the phase difference calculation unit 13 calculates tan -1. The deviation from point X or X' in Figure 3 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, and if the output of the integrator 5 is not 0, the change in induced voltage V ₂ due to the change in lift-off d is removed. After the
It is added to the frequency converter 15 and converted into a change in frequency Δf of the primary coil excitation current necessary to make the output of the phase difference calculator 13 0, and is converted into a frequency change Δf, which is applied to the frequency-temperature conversion calculator 16 and the oscillation frequency control circuit 17.
added to. In the oscillation frequency control circuit 17, the oscillator constant is changed so as to change the frequency of the high frequency oscillator 18 by Δf. In the frequency-temperature conversion calculator 16, the frequency change Δf is calculated as follows: Ko・fo=μ/σ Ko・(fo+Δf)=μ/σ+Δ(μ/σ) ...(5), Δ(μ/σ)=Ko・(fo+Δf)−μ/σ=Ko・(fo+
It is converted into Δ(μ/σ) using the following relationship and output as a temperature change. Here, Ko is the value of K=μ/σ×f at point X or point X', and fo is the current frequency of the high-frequency oscillator 18.

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 deviations from the current frequency, so it is possible to By setting in advance the points on the complex voltage plane and the corresponding excitation frequencies, it is possible to measure temperature with high precision 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: 25×10 ^-3 [m] Primary coil outer radius: 30×10 ^-3 [m] Secondary coil inner radius: 10×10 ^-3 [m] 2 Primary coil outer radius: 15×10 ^-3 [m] Coil length: 10×10 ^-3 [m] Number of turns of primary coil: 40 [Turn] Number of turns of secondary coil: 100 [Turn] Primary current: 0.25 [A] ], and the values of μm and fμ in this case are μm≒120×4π×10 ^-7 [H/m] and fm≒115 [KHz], respectively. With the above coil configuration, the standard excitation frequency is 50KHz for the work roll temperature range of 20 to 300℃.
For a temperature range of 300 DEG C. to 600 DEG C., the reference excitation frequency was set to 175 [KHz], and as a result, measurement was possible with sufficient accuracy.

As described above, according to the present invention, the temperature at and near the surface of a magnetic material having a thickness larger than the dimensions of a detection coil, such as a rolling roll, can be measured non-contact and with high precision over a wide temperature range. Even if there is an oil film or water film on the surface of the object to be measured, or even if the object is moving at high speed, stable temperature measurement is possible without being affected. This expands the possibility of temperature measurement in areas where it has been difficult.

[Brief explanation of the drawing]

Figure 1 is a front view showing the configuration of the eddy current detection coil;
Fig. 2 is a diagram for explaining the behavior of the secondary coil induced voltage on the complex voltage plane, and Fig. 3 is a diagram for explaining the setting of a specific point on the complex voltage plane of the secondary coil induced voltage in the present invention. FIG. 4 is a block diagram showing the circuit configuration of an apparatus in an embodiment of the present invention. 20: Detection coil, 1: Primary coil, 2: Secondary coil, 4, 8, 11: Synchronous detector, 6, 7, 1
0: Phase shifter, 5, 9, 12: Integrator, 13: Phase shift difference calculator, 14: Lift-off fluctuation correction calculator,
15: Frequency converter, 16: Frequency-temperature conversion calculator, 17: Oscillation frequency control circuit, 18: High frequency oscillator, 19: Reference phase difference calculator.

Claims (1)

[Claims] 1. In a temperature measurement method using a probe-type eddy current detection coil in which a secondary coil is coaxially arranged inside a primary coil, the induced voltage in the secondary coil is expressed on a complex voltage plane. is determined at one point on the complex plane by the following parameter K. Under a specific range of the magnetic permeability of the measured object or the excitation frequency of the primary coil, which is the measurement condition, the induced voltage is determined in advance at one point on the complex plane. Set the primary coil excitation frequency at which is a specific point on the complex voltage plane, find the amount of change in the excitation frequency necessary to eliminate the deviation of the actual induced voltage from the specific point during measurement, and calculate this frequency. An eddy current temperature measurement method characterized by determining the amount of change in temperature of an object to be measured from the amount of change. Parameter K = (magnetic permeability of the object to be measured) / (electrical conductivity of the object to be measured) x (excitation frequency)