FI88210C - REFERENCE TO A TREATMENT OF TEMPERATURE IN THE STEM OF ARONE - Google Patents

Description

METHOD AND APPARATUS FOR TEMPERATURE OF ELECTRIC CONDUCTIVE MATERIAL

MEASURING

! 8821 J

The invention relates to a method for measuring the temperature of an electrically conductive substance as defined in the preamble of the independent claim. The invention also relates to a device for carrying out the method. The method and apparatus can be used to measure the temperature of a hot, solid or molten electrically conductive substance or body 10 without contact between the measuring sensor and the measuring object.

High temperatures of several hundred or thousands of degrees (° C) are currently measured mainly by two devices: a pyrometer and a thermocouple. 15 The first is based on measuring the thermal radiation emitted by the object to be measured. The second is based on the thermoelectric effect.

The measurement performed with a radiation pyrometer is non-contact. This device can be used to perform 20 measurements at a moderate distance from the target. A weakness of the radiation lipyrometer, for example in measurements in the metallurgical industry, is the dependence of the emissivity of the radiating body not only on the temperature but also on the radiating substance. Thus, for example, in the measurement of the temperature of a metal surface, the oxide scale layer on the surface or the slag layer on the surface of the molten metal can cause considerable errors which are difficult to compensate for. Likewise, smoke, dust, water vapor, etc. surrounding the measurement object causes an error.

30 The thermocouple is commonly used especially for measuring the temperature of metal alloys. This is a direct measurement, i.e. the thermocouple is immersed in the measuring object. The problem is the aggressiveness of the circumstances. The measuring sensors are generally disposable and the measurements are thus spot-on. When aiming for continuous measurements, protective tubes must be used, in which case the '· - measurement delay of the element increases due to the slow heat transfer.

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For practical reasons, it is difficult to perform the temperature measurement of moving hot bodies, e.g. castings and rolling billets, with a thermocouple. The elements attached to the surface of the part have only been used for research purposes.

It is known that the noise of a linear electrical circuit in thermal equilibrium is directly proportional to temperature. In general, this law is given in the dissociation theorem, which, when applied to an electrical resistor, gives the so-called Nyquist's theorem. Applying this theorem, a noise thermometer has been constructed to realize the temperature using the Bolzmann constant. This principle has been used in accurate temperature determinations at both low temperatures and very high temperatures. In these measurements, noise is measured from a resistor that is thermally anchored to the object being measured. The use of the method and the device for measuring the temperature of hot and especially moving objects prevents the destruction of the connecting wires, contacts and the resistor itself at high temperatures.

It is an object of the present invention to provide a new improved method and apparatus for measuring the temperature of an electrically conductive substance, with which the temperature of a body or other object can be measured without contact. With regard to the features of the invention, reference is made to claim 1 for the method and to claim 7 for the device.

The method according to the invention is based on the measurement of thermal noise by means of a resonant circuit without contact with the substance to be measured, in particular a hot body. The method measures the fluctuation of a magnetic field generated by the random movement of charge conductors in a metal or other conductive material from a distance from the surface of the material.

The advantages of the method and device according to the invention can be stated as follows. The measurement can be performed without touching the object to be measured. Also, the insulating material, air, dust, water vapor and other contaminants between the object to be measured and the sensor do not significantly interfere with the measurement. Thus, the method and device 5 are particularly well suited for industrial measurements, such as temperature measurement of hot metal casting and rolling billets. The measurement can also be performed on continuously moving blanks. The method also makes it possible to measure the temperature of the metal melts through the insulating liner material layer 10. Under well-controlled laboratory conditions, the measurement can be performed with very high accuracy, so the method can be used as a temperature reference, e.g. in the calibration of thermocouples or pyrometers.

In the following, the invention and its other advantages will be described in detail with the aid of the accompanying drawings, in which Figure 1 shows a block diagram of an apparatus according to the invention; J '20 Fig. 2 shows a noise model of the device of Fig. 1; Figure 3 shows a device according to the invention in a perspective view and in partial section; Figure 4 shows a block diagram of another device according to the invention and a measuring part connected thereto; Figure 5 shows the measurement results obtained with a device according to the invention from a steel test piece.

Based on Nyquist 's theorem, an electrical resistor in thermal equilibrium with respect to its environment' · '· can, when fitted, supply kBT of noise energy per unit band to 30 at absolute zero temperature. resistance. This only applies at low frequencies, because • · at high frequencies, thermal energy is discharged into the environment in quantums and the power transfer per band unit • · becomes frequency dependent. This phenomenon only occurs at very high frequencies, so that from the point of view of the method and device according to the invention, the power is evenly distributed over the different frequencies. Simplified 4 88210

Nyquist's theorem means that each electrical loss is associated with a thermal noise voltage, the magnitude of which depends on the temperature T, the magnitude of the resistance R, and the noise bandwidth Bn associated with the noise measurement. Accordingly, the generation of noise can be described as an equivalent current generator connected in parallel with a resistor. That is, <e2> = 4kBTBNR (1) 10 <in> = 4kBTBN / R (2) where kB is the Bolzmann constant (1.38 x 10-23 w / κ). Equations (1) and (2) no longer hold when the energy associated with the quantum hf (h is the 15 Piano constant and f is the quantum frequency) approaches the thermal energy kBT.

In the device according to the invention, the losses of the object 1 to be measured in Figures 1 and 2 are transferred to the input of the amplifier 2 by means of a partially open resonant circuit 3. In this case, the reso-20 dance circuit 3 is formed by a coil 4. The inductance of the resonant circuit is L * and its loss resistors are reduced to one parallel resistor R * and the corresponding noise current generator i *. The parallel resistance Rx describes the 25 equivalent losses in the resonant circuit 3 of the object to be measured 1 and the current noise caused by the losses, respectively. Since the conductive body 1 also affects the distribution of the external field, the inductance L of the resonant circuit depends on the distance s between the coil 4 and the object 1. Using static shields 30, the inductance of the coil 4 can only be considered variable, L *, and ) the change is represented by the variable inductance Lx. The noise of the amplifier in Figure 2 is illustrated by the current and voltage noise generators placed at the input i £ et ;, e £ et. respectively. The load capacity of the amplifier is described by the resistor Rf. The temperatures Tx, T * and represent the temperature of the object to be examined, the noise temperature of the coil 5,88210 and the noise temperature of the amplifier, respectively. All the capacitances of the circuit are included in the capacitor C and are assumed to be independent of the distance s between the object 1 and the sensor 5, which at its simplest consists of the coil 5 4 and the amplifier 2. It should be noted that

After the amplifier 2, the noise can be detected by a suitable detector or measuring part 6 either directly 10 or by mixing the noise at low frequencies and detecting with a suitable detection circuit.

In one method and device according to the invention, the noise is mixed down at a frequency corresponding to the resonant frequency 15 w0 = i / (lc) of the resonant circuit 3. Figure 4 shows such a device. The measuring part 6 corresponds to the detector part of Fig. 1. The measuring part 6 includes a high-pass filter 7, a voltage-controlled oscillator 8, two mixers 9, 10, high-pass filters 11, 12, an adder 13, an rms converter 14, a voltage amplifier 15 and current amplifiers or integrators 16, 17. a summing amplifier 18 and, if necessary, a switching capacitor 19.

The high-pass filter 7 of the measuring section 6 is connected to the mixers 9 and 10. The output terminals 8a, 8b of the voltage-controlled oscillator 8 25, from which the cosine and blue signals are obtained, respectively, are connected to the mixers 10, 9, respectively. . respectively. The outputs of the mixers 9, 10 are connected to the high-pass filters 11, 12. The outputs of the high-pass filters 11, 12 are connected to the inputs of an adder 13, the output of which is: V: 30 connected to an rms converter 14, from which the actual measurement signal the output terminal 8b of the oscillator 8 is connected via the amplifier 15 to the second input terminal 18b of the summing amplifier 18 of the sensor 5. The output terminal 8a 35 of the voltage-controlled oscillator 8 is connected via a switching capacitor 19 to the input of the amplifier 2 of the sensor 5. The output of the amplifier 2 is in turn connected to the first input terminal 18a of the summing amplifier 18. The output of the mixer 9 is connected via a current amplifier 16 to the second input terminal of the amplifier 15, through which the gain can be adjusted. The output of the mixer 10 is connected via a current amplifier 17 to the input of a voltage controlled oscillator 8.

The noise measured in the apparatus according to Fig. 4 is mixed down at a frequency corresponding to the resonant frequency ω0 = 2nf0 of the resonant circuit 3. Due to interference, the mixed signal must be filtered by a high-pass filter 10 with a response 7 (H ^ Jui). Taking into account the response of the resonant circuit and the filter 11, 12 after the mixer 9, 10, the variance of the output voltage can be given in the form 15 (3) 20 <U => = ^ a ^ «y” [[l + g5e (l - (- ^) 2)] -a + i | Η * "<ί (ω-ωο)) | 2 <3ω 25 where the equivalent temperature T. of the resonant circuit can be expressed by the temperatures of the various components as follows: 30 T. = R (- |« - + + i) ( 4)

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35 The load resistance R of the resonant circuit is obtained from the equation R-1 = (1 / RX + 1 / R * + 1 / Rjr) (5) 40 In Equation 3 u, the characteristic frequency of the coil is R / L. The noise temperature of the amplifier is T * when the supply impedance is optimal R * 0 · Both Te and Rro are characteristic constants of the amplifier.

When the resonant frequency ω.β and the total impedance R of the resonant circuit 3 are measured, the temperature 45 Tx of the test piece 1 can be unambiguously determined from Equations (3) to (5).

If the coupling to object 1 is very good R ® Rx, then T. «Tx. Furthermore, if it is assumed that the noise temperature of the amplifier is small, i.e. T * << Tx and the high-pass filter 11, 12 after the mixer 9, 10 is clearly wider than the bandwidth of the resonant circuit 3, Equation 3 is reduced to the simple form 5 <U20> = A2kBTx / C (6) where A is the total gain before detection and C is the capacitance of the resonant circuit. It can be shown that the bandwidth of the filter Hm (joj) should be chosen close to the bandwidth of the 10 resonant circuits, so in practice the resistance R and the resonant frequency ω 0 of the resonant circuit 3 must be measured and Tx calculated from these results.

Essential to the above equations is that the expressed voltage <U2> is an unambiguous function <U02> = f (Tx / R, w0) of the temperature Tx of the object to be measured and the loaded resistance R and resonant frequency ω0 of the coil 4, i.e. the object temperature Tx = g '· * ·' (<U02>, R, «J0). The correction can be performed either by using Equations (3), (5) or by measuring the output voltage; 20 at different temperatures and at different distances and fitting the results of j γ to some suitable mathematical model.

Y; The target temperature Tx is determined by measuring the • k variance of the amplified voltage. The variance (temperature measurement inaccuracy) of the measured variance o2 depends on the measurement time τ and the equivalent noise bandwidth B „according to the following equation: 30 Var [o] = - | --- (7) · '·' The relative resolution of the temperature measurement is Y: thus ε = / j ^ T / T = (Ββτ) “*. If the resonant circuit is tuned to a frequency of about 1 MHz, it is possible to achieve a noise band of 100 kHz, so that a measurement time of 10 seconds results in a resolution of 10_3. The final inaccuracy - "is determined by the measurement inaccuracy of the impedance, changes in the noise temperatures of the amplifier and the open coil 40, and possible disturbances.

In the device according to Fig. 4, current is supplied to the resonant circuit 8 88210 3 via a capacitance 19 from the output 8a of the voltage-controlled oscillator 8 and the voltage from the output 8b via an adjustable amplifier 15. When the resonant circuit is purely real, the output signal of the summing amplifier 5 18 is 90 ° out of phase with the cosine signal of the oscillator output 8a, and thus the output of the phase detector 10 is set to zero and the output of the voltage controlled oscillator control integrator 17 remains in place. If the voltage induced in the resonant circuit 3 of the current supplied through the output of the voltage controlled oscillator 10 8a does not cancel the voltage summed therein in the summing amplifier 18, the output of the phase detector 9 is also not set to zero and thus the gain of the gain adjuster 16 The output of both integrators 16, 17 is set to zero only when the resonant circuit 3 is supplied at the resonant frequency and if the voltage applied to the amplifier 18 cancels the voltage coming from the resonant circuit; the output of the integrator 16 thus becomes equal to zero to the real part R of the impedance of the resonant circuit 3 in the resonance, while the output of the integrator 15 becomes directly proportional to the resonant frequency ωβ. The signals related to the measurement of impedance R and resonant frequency β are low-charge after 25 mixers and are filtered by high-pass filters 11 and 12. After these filters, noise signals proportional to the temperature T * of the object to be examined are .

If necessary, one or more suction circuits tuned to the frequencies of radio stations close to the resonant frequency can be added to the measuring section 6. In this way, the interference caused by these radio stations 35 for the measurement can be avoided.

The detection voltage U obtained from the measuring section 6 can be transferred to a data processing unit such as a miniature data 9. 88210, via an A / D converter and used, for example, to control or monitor the process.

Figure 3 shows a device according to the invention, in particular a sensor 5, in a perspective view and 5 in partial cross-section. The sensor 5 comprises a coil 4, which in this case is a coil 3b with a ferrite core 3a, which is arranged inside a suitable body 3c, such as a Teflon body. The coil 4 is placed at a distance s from the material whose temperature Tx is to be measured, as already described above. The sensor 5 further comprises a preamplifier 2 and possibly a mixing amplifier 18 (Fig. 4). The preamplifier 2 is placed on the preamplifier board 2a in the immediate vicinity of the coil 4. The sensor 5 is mounted inside a static shield, in this case a body 15 20, which is a conductive material such as copper.

In connection with the body 20 there is a cooling device 21.

. . The cooling device 21 is preferably formed by a tubular member helically wound around the body 20 and placed at the end of the body to which the coil 3 is fitted. Via the cooling device: V is supplied with a suitable coolant when the 'measurement' is carried out.

: Y: A cover plate 22 or the like is arranged in the body 20 between the coil 4 and the substance to be measured. This is a heat-resistant and neutral material such as sapphire. The coil 4 of the sensor 5 is in principle constructed in such a way that. . that it is as insensitive as possible to homogeneous • I ·; ; for magnetic fields, in which case it only measures the fluctuations of the magnetic field generated on the surface of the object to be measured.

Figure 5 shows the output U0 of the rms value converter *. * 14 when heating a steel test piece.

• · y'm The left vertical axis of the figure shows the square of the rms value of the noise voltage <Uo>, which represents the measured temperature 35 (K) according to formula 3. The impedance of the coil 3 at the resonant frequency is shown in the right vertical axis. The horizontal axis is steel temperature 10 8821 0 (K) The results shown are normalized by multiplying them by a constant, the rms value of the noise depends linearly on the temperature of the steel and therefore in these measurements the temperature is obtained using the formula = U02 / R + B, 5 where A and B are constant. the square of the rms value <U „> follows the iron surface temperature Tx well.The accuracy of the device can be improved by increasing the measurement band, which can be achieved by increasing the resonance frequency 10. When operating at high frequencies, the amplifier noise temperature can be lowered and the preamplifier cooled.

It can be stated that the device according to the invention for measuring surface temperatures can be realized so that the measurement accuracy is less than ± 3K. A very accurate device according to the invention for measuring surface temperatures can be realized by replacing the copper coils of the coil 3 with superconducting windings, which are preferably made of ceramic materials. Superconducting windings made of ceramic 20 materials are already operating at the temperature of liquid nitrogen (+77 “K).

In the above, inductance has been used as the reactance in the resonant circuit 3, but it is clear that capacitance can also be used instead. In this case, instead of a capacitance, such as a capacitor, adjusted to the resonance 25, instead of an inductance, such as a coil, the impedance of the object to be measured is adjusted to suit a low-noise preamplifier. The measurement is performed completely analogously based on the method presented above.

The invention has been described above mainly with reference to one preferred embodiment thereof, but it is clear that the invention can be modified in many ways within the scope of the inventive idea defined by the appended claims.

35

Claims (12)

1. A method for measuring the temperature of a conductive substance, which method is based on the measurement of thermal noise in the substance, characterized in that the fluctuation in the magnetic field generated by the random charge of the charge substance present in the conductive substance motion, is measured by means of a resonant circuit (3) which is out of contact with the substance (1) to be measured. 2. A method according to claim 1, characterized in that the measured high frequency noise is mixed down at low frequencies and detected. 3. A method according to claim 2, characterized in that the mixing is performed at the frequency of the resonant circuit (3). Method according to claim 2 or 3, characterized in that the mixed noise signal (<U *>) is detected and the resonant frequency (ωο) and resistance (R) of the resonant circuit (3) are measured and these results are calculated. temperature of the article to be investigated (Tx). 5. A method according to claim 4, characterized in that the resistance (R) of the resonant circuit (3) is measured by measuring the current current (I) and voltage (U) with a phase opposite thereto and that the frequency and the amplitude of the current are controlled so that the signals generated by the current and voltage cancel each other, whereby at the equilibrium position from the frequency, the resonant frequency (ω) is obtained directly and the relationship between the voltage and the current (U / I) is directly proportional to the resistance (R) of the resonant circuit (3). Method according to any of the preceding claims 3 or 4, characterized in that the sub-frequencies are filtered off from the signal after mixing to eliminate interference and that the filtering is done on a bandwidth which is at least approx. Ί ΰ corresponds to the bandwidth of the resonant circuit (3). 7. Apparatus for measuring the temperature of a conductive substance, by which apparatus is measured at low-frequency thermal noise and, on the basis of this, the temperature is determined, characterized in that the device belongs - a detector (5), in which there is a resonant circuit (3), whose reactance portion is located at a distance (s) from the substance (1) whose temperature is to be measured; 10. a preamplifier (2); and which detector (5) is installed inside the body (20), which consists of a conductive material such as copper. Apparatus according to claim 7, characterized in that there is in connection with the body 15 a cooling device (21). Device according to claim 7 or 8, characterized in that a protective split (22) or the like, which consists of a heat-resistant neutral substance is arranged between the reaction part and the substance to be measured. dachshund. silicon or sapphire. 10. Device according to claim 7, characterized in that the reactant part consists of a coil (3) which has been realized with a superconductor winding which has advantageously been made of a ceramic superconductor. Device according to any of the preceding claims, characterized in that the device additionally comprises a measuring part (6) which contains at least one mixer (9, 10) and a detection circuit (14), with the aid of which measured noise is mixed down at equal frequencies. 12. Device according to claim 11, characterized in that the device further comprises a summing amplifier (18) adapted to the detector (5) and a high-pass filter (7) connected to the measuring part (6), a voltage controlled oscillator (7). 8) with the 16 3 8 2 Ί ϋ outputs (8a, 8b) for cosine and sine signals, two mixers (9,10), high-pass filter (11, 12), a summator (13), a power value converter (14), a voltage supply amplifiers (15) and two integrators (16, 17), which 5 high-pass flutes (7) are connected to the outputs (9, 10), the outputs (8a, 8b) of the voltage controlled oscillator (8) are similarly connected to the outputs (8). 10, 9), the outputs of the mixers (9, 10) are connected to the high-pass filter (11, 12), and the outputs of the high-pass filter (11, 12) are connected to the inputs of the summator (13), the output of which is connected to the power value converter, whereby a measurement signal (U () comparable to the temperature of the measuring object is output, and in which the voltage The output (8b) of the controlled oscillator (8b) via the amplifier (15) is connected to the detector (5) to one input pole (18b) of the summing amplifier (18) and the output (8a) of the voltage controlled oscillator is connected to the detector (5). ) the input of the amplifier (2) and the output of the amplifier (2) are connected to the first input coil (18a) 20 of the summing amplifier (18) and furthermore the output of the mixer (9) is connected to the second input coil of the amplifier (15). and the output of the mixer (10) via the current amplifier is connected to the input of the current controlled oscillator (8).