JP5298388B2 - Temperature measuring method and temperature measuring apparatus using ultrasonic waves - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for measurement of temperature, capable of carrying out stable measurement by practically measuring the ultrasonic receiving time while being hardly affected by amplitude fluctuation. <P>SOLUTION: The method includes receiving ultrasonic waves transmitted from a transmitter by a receiver which is the same as or different from the transmitter, and measuring a propagation time of propagating in a region to be measured, to compute the propagation speed of the ultrasonic waves and to measure the temperature of the region. An envelope peak point on the receiving side is set to a reference point of the receiving time to transmit positive phase waves for a predetermined time, and then reverse phase waves controlled in amplitude and wave number are transmitted to improve the accuracy in detecting the receiving time and the accuracy in temperature measurement. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a non-contact type temperature measuring method and apparatus using ultrasonic waves.

Conventionally, thermocouples, thermistors, alcohol thermometers, etc. are used for temperature measurement.
In these temperature measurement methods, the temperature of the portion in contact with the sensor is measured, and therefore, only the temperature at one point in space can be measured.
In order to measure the temperature of the entire area of the space, a large number of sensors must be installed, which causes a problem that the scale becomes large and the cost is high.
Thus, for example, Japanese Patent Application Laid-Open No. 2003-130735 or Japanese Patent Application Laid-Open No. 2000-329623 discloses a method for measuring the temperature of the spatial region in a non-contact manner using ultrasonic waves.
In the temperature measurement using ultrasonic waves, the average temperature of the propagation path can be measured in a non-contact manner, and there is no need to consider the heat capacity of the sensor itself.
Further, by changing a plurality of ultrasonic propagation paths, the temperature distribution can be measured in a non-contact manner without arranging a large number of sensors in the space.

  Ultrasonic temperature measurement having such characteristics is disclosed in the room disclosed in Japanese Utility Model Laid-Open No. 1-170942, the vehicle disclosed in Japanese Patent Laid-Open No. 6-194237, and the vinyl reported in Non-Patent Document 1. It can be expected to be applied to temperature monitoring technology related to air conditioning of long-distance spaces in houses.

As a temperature measurement method using the aerial ultrasonic wave, a method using the fact that the propagation speed depends on temperature is known, and in this case, it is necessary to accurately determine the propagation time of the ultrasonic wave.
However, since general-purpose piezoelectric ultrasonic sensors that are generally used use a narrow-band resonator to increase the sensitivity, even if the envelope is driven by a rectangular pulse, The waveform is deformed.
The transmitted signal needs a wave number until it reaches a sufficient amplitude level, and it is difficult to identify the received first wave.
Broadband speakers and microphones are also commercially available, but they have a problem of being expensive or large.
Even if an ultrasonic wave having a rectangular envelope can be transmitted, the waveform is deformed in the propagation process of the ultrasonic wave due to the influence of high propagation attenuation depending on the frequency.
As a countermeasure, it is necessary to set the reception reference time instead of the received first wave.
As a reference time setting method, a method of using a time corresponding to a voltage threshold has been widely used.
However, in practice, for example, if the amplitude of the ultrasonic signal fluctuates or deforms due to factors such as the influence of airflow or changes in humidity, it is difficult to accurately determine the reception time.
A method using a threshold generally has a poor S / N, and it is difficult to measure with high accuracy.
As a measure for improving the method using a threshold, a method of combining time information and phase information is disclosed in, for example, Japanese Patent Laid-Open No. 6-194237.
However, this method, in principle, requires time information to be determined with an error that is less than or equal to the period of the ultrasound, and the conventional time measurement method that uses a threshold value provides sufficient accuracy, particularly in environments with low S / N. Often not.
If the time information cannot be determined with an error equal to or less than the period of the ultrasonic wave, for example, as disclosed in Japanese Patent Laid-Open No. 6-194237, it is determined and corrected whether the phase change amount before and after the measurement exceeds one period. However, it is necessary to always measure the phase, and it is difficult to respond if the temperature changes suddenly.
As another method, for example, a method using a phase modulation point at which the amplitude of an ultrasonic waveform formed by an amplitude and phase modulation signal in Non-Patent Document 3 becomes zero, or a method using an envelope peak time as in Non-Patent Document 2 Has been proposed.
However, since the former uses a value near zero amplitude, the S / N is poor, and in the latter, the ultrasonic wave transmitted from the general-purpose sensor has a gentle rise and decay of the waveform and a gentle envelope. It is not easy to detect.
It is also conceivable to introduce a technique based on a method for obtaining a correlation between a received signal and a reference wave.
However, in general, a waveform of a long time is required, and there are problems such as the influence of multipath in which a direct arrival wave and a reflected wave from an obstacle interfere with each other, and calculation processing is complicated.

JP 2003-130735 A JP 2000-329623 A JP-A-6-194237 Japanese Utility Model Publication No. 1-107942 JP 2007-85867 A

Kudo et al., Plant Environmental Engineering, 17 (3) (2005) 121 J. F. Figueroa et al., J. Acoust. Soc. Amer., 91 (1) (1992) 486. Y. S. Huang et al., Rev. Sci. Instrum., 78 (2007) 115102. Kikuchi et al., Tohoku University Den-Den-Denki Talk, 40, 4 (1971) 219.

  In view of the above-described background art, the present invention provides a temperature measurement method and a temperature measurement apparatus that are not easily affected by amplitude fluctuations and that enable stable measurement by making ultrasonic wave reception time practical. With the goal.

In the temperature measurement method using ultrasonic waves according to the present invention, the ultrasonic waves transmitted from the transmitter are received by a receiver that is the same as or different from the transmitter, and the propagation propagates through the region to be measured. This is a method of measuring the propagation speed of ultrasonic waves by measuring time and measuring the temperature of the region, setting the envelope peak point on the receiving side as the reference point of the receiving time, and positive phase for a predetermined time After transmitting a wave, an anti-phase wave whose amplitude and wave number are controlled is transmitted, thereby improving the detection accuracy of the reception time and improving the accuracy of temperature measurement.
Here, the amplitude of the driving signal of the antiphase wave is larger than the amplitude of the driving signal of the antiphase wave, and the wave number of the driving signal of the antiphase wave is larger than the wave number of the driving signal of the positive phase wave. It is also characterized by a few points.
Further, the detection accuracy of the received time may be improved by detecting the time of the zero cross point immediately after the received envelope peak time as a reference.

A temperature measuring device using ultrasonic waves according to the present invention includes a transmitter that transmits ultrasonic waves and a receiver that is the same as or different from the transmitter, and has a propagation time for propagating in a region to be measured. This is a temperature measurement device that can measure the propagation speed of ultrasonic waves by measuring and measure the temperature of the region, and transmits an antiphase wave whose amplitude and wave number can be controlled arbitrarily after transmitting a positive phase wave for a predetermined time. Transmission control means for performing the operation and envelope peak time detection means.
Here, it may have a zero cross time detecting means for detecting the time of the zero cross point immediately after the envelope peak time using the envelope peak time detecting means.

Next, the measurement principle of the present invention will be described.
For example, when a drive signal oscillated from an oscillator is applied to a general-purpose transmitter and the signal is transmitted, an ultrasonic waveform as shown in FIG.
By adding an antiphase signal (FIG. 1 (b)) to the ultrasonic waveform shown in FIG. 1 (a), residual vibration starting from the vicinity of the peak in FIG. 1 (a) can be suppressed, and the peak point of the envelope is set. It is possible to emphasize (FIG. 1 (c)).
Thereby, the envelope peak point can be clarified, and the reference point of the ultrasonic wave reception time can be detected with high accuracy.
In particular, it is possible to detect the time with a smaller number of measurement points or a narrower waveform measurement range.
Further, as shown in FIG. 1 (d), by detecting the time of the zero cross point after an integer multiple cycle of the envelope peak time (circle in the figure) (after 0 cycle in the example of FIG. 1 (d)), More accurate measurement is possible.
This is because a long ruler that determines which zero-cross point to focus on can be accurately determined based on the peak time, and a final short ruler can be obtained by measurement of a phase level that is not affected by amplitude fluctuation.

FIG. 2 is a block diagram showing an embodiment of the above signal processing procedure.
First, an envelope of the ultrasonic wave reception waveform is obtained by the envelope derivation means 11, and the peak time is obtained by the envelope peak time detection means 12.
Next, the time difference between the zero cross point obtained by the phase detection means 13 and the peak time is obtained by the final time difference determination means 14, and the zero cross point at which the time difference becomes the minimum or the zero cross point after the integer multiple cycle is received time. And
Furthermore, the time difference T between the final transmission and reception signals is added to the final time difference by adding the amount of change in reception time when the temperature changes from the reference value to the time difference between the transmission and reception signals calibrated at a fixed reference temperature. It can be determined by the determination means 14.
Using this time difference T and a known ultrasonic propagation distance L, a propagation velocity c is obtained by the following equation.
The ultrasonic wave propagation velocity c and the average temperature t of the path through which the ultrasonic wave propagates have the following relationship.
However Equation (2) because humidity is a relational expression when 0%, obtains the ratio CF h of propagation velocity c _d when propagation velocity c _h a humidity of 0% is the humidity _(correction coefficient humidity), c _The temperature t is calculated by substituting _h and CF _h into the following equation.
CF _h is a function of temperature and relative humidity, and can be obtained by measuring the relative humidity.
The propagation speed obtained by the equation (1) and c _h, by substituting the equation (3), calculates the temperature t.

By using the reverse phase signal, the residual vibration of the ultrasonic signal is suppressed, and the envelope peak point is clarified, so that the reception time can be detected with high accuracy.
In particular, time detection can be performed with a smaller number of measurement points or a narrower waveform measurement range.
Furthermore, by combining with phase information, a more accurate temperature measurement system that is hardly affected by amplitude fluctuations can be obtained.
In addition, by introducing an antiphase signal, the envelope peak position can be formed at an early time, and since the vicinity of the peak is sharp, it becomes a practical system that is relatively resistant to multipath.

In the field of ultrasonics, the concept of canceling the other residual vibration by two drive signals is mostly studied for an underwater ultrasonic sensor as described in Non-Patent Document 4, for example, and the purpose of the residual vibration is also determined by a braking signal. It is in the point that the characteristic of the ultrasonic pulse width is improved by canceling out cleanly.
An application example to an aerial sensor is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-85867.
However, this example is similar to the above purpose.
On the other hand, the present invention is intended to accurately determine the ultrasonic propagation time by forming a characteristic reference time when the ultrasonic wave is received. It has features such as greatly changing the amplitude of the signal.
Usually, when the amplitude of the antiphase signal is increased, overbraking occurs, so such a concept is difficult to consider, but it is an effective technique for achieving the object of the present invention.
By sharpening the peak point in this way, the object is to improve the accuracy of time detection and reduce the influence of multipath.
Further, the present invention is characterized in that the time detection accuracy is further improved by combining the time thus obtained and the phase information, and the spatial temperature is measured with high accuracy. And the method is different.

Conventionally, the temperature of a part of the measurement space was measured with a thermocouple, thermistor, alcohol thermometer, etc., but the system of the present invention measures the average temperature of the space in a non-contact manner with a pair of ultrasonic sensors. Is possible.
Alternatively, temperature measurement can be performed in a non-contact manner without introducing a large facility such as arranging a plurality of sensors in the measurement space.
Furthermore, since the ultrasonic wave does not need to consider the heat capacity of the sensor itself, it is possible to perform temperature measurement with relatively better response than the conventional sensor.

Because it can measure the space temperature in a specific area without contact, it can be expected to be applied to temperature measurement in long-distance space.
Since ultrasonic propagation in the air has a large propagation attenuation depending on the frequency, it is difficult to obtain a sufficient S / N in temperature measurement for long distances. However, by using the system of the present invention, low S High-precision temperature measurement is possible even in an / N environment.
With such a feature, it is possible to measure a long-distance spatial average temperature about 10 m without contact.

In addition, it can be expected to be applied to indoor environment temperature monitoring and temperature control technology using wall reflection in the room.
The measurement using the reflected wave of the ultrasonic wave requires a system having a high S / N because the propagation distance is twice as long as that of the transmission method, but this can be realized by using the system of the present invention.
Furthermore, if reflected waves from a plurality of wall surfaces are used, there is a possibility that the temperature of each region in the room can be measured in a non-contact manner with a small number of ultrasonic sensors.

Further, even when there is an obstacle in the vicinity of the ultrasonic wave propagation path during the temperature measurement, by using this system, it is difficult to be affected by the reflected wave from the obstacle, and practical restrictions can be reduced.
With the present invention as described above, various applications are possible, and it can be expected to support energy saving and comfortable space.

The principle explanatory view of the ultrasonic propagation time measurement concerning the present invention is shown. The example of the flowchart of the signal processing means which concerns on this invention is shown. 1 shows a system configuration example of a temperature measuring device according to the present invention. The example of the drive signal (a) which concerns on this invention, and the example of the received waveform (b) are shown. An example of a conventional drive signal (a) and its received waveform (b) are shown. An example of evaluation of a 3 dB pulse width when the amplitude ratio k and the wave number n of an antiphase signal are changed is shown.

FIG. 3 shows a system configuration diagram showing an embodiment of a temperature measuring device based on the configuration of FIG.
The drive signal oscillated from the oscillator 21 is amplified by the amplifier 22 and then applied to the transmitter 23 to transmit the ultrasonic wave in the air, and the ultrasonic wave propagated in the air by the distance L is received by the receiver. Receive at 24.
An example of a signal for driving the transmitter and its received waveform is shown in FIGS. 4 (a) and 4 (b), respectively.
The first positive phase signal in the figure is a signal for raising the generated ultrasonic signal to some extent and obtaining an appropriate amplitude level.
Based on the above principle, the next anti-phase signal suppresses the residual vibration after the vicinity of the peak of the conventional received waveform [FIG. 5B] when driven by the signal of FIG. This is a signal for clarifying the peak point.
In FIG. 4A, the amplitude ratio of v ₁ and v ₂ is k = v ₂ / v ₁ , the wave number of the anti-phase signal is n, and the delay time t _d of the anti-phase signal with respect to the positive phase signal.
The amplitude ratio k and the wave number n are changed (t _d = 20T _period (T _period is the _period of the ultrasonic wave)), and the result of obtaining the 3 dB width of the envelope of the received waveform as an index of the sharpness of the envelope is shown in FIG. Shown in the graph.
From the graph, when the amplitude ratio k = 1, n = 10 is sufficient.
In addition, it was found that increasing 3 k can shorten the 3 dB width and is more effective than k = 1 and n = 10.
Further, it was found that a wave number as small as n = 4 is sufficient for k = 2, n = 3 for k = 5, and n = 2 for k = 10 and 20.
Considering the power consumption and the result of the graph, it is not efficient to increase k to 10 or more.
From the above, after setting n to the minimum necessary in the range of k = 1 to 10, it may be set according to purposes such as accuracy and power consumption.
As an example, a received waveform example of k = 10 and n = 2 is as shown in FIG. 4B, and it can be seen that the peak point is sharper and clearer than the conventional waveform of FIG. 5B.
Since the amount of change in the inflection point of the envelope is large, the peak point can be detected with high accuracy.
In addition, since the pulse width is short, the waveform analysis range may be narrower than in the prior art.
The delay time of about t _d, which form a peak point in time earlier by a shorter, may be configured to facilitate the identification of the reflected wave by directly reaching wave and the obstacle.
The analog signal received by the receiver 24 is amplified by the amplifier 25 and then A / D converted by the A / D converter 26 to be converted into a digital signal.
After this signal is written in the memory by the memory means 27, the derivation of the envelope and the zero cross point are detected by the arithmetic unit.
The envelope is derived by, for example, obtaining the approximate curve after obtaining the carrier peak of the received signal.
After that, the reception time corresponding to the envelope peak value is calculated, and if necessary, the zero cross point after an integer multiple of that time is obtained, and this is used as the reception time to accurately calculate the ultrasonic propagation time. calculate.
The temperature t is calculated and displayed by substituting the propagation speed c obtained by substituting the received time into the equation (1) into the equation (2).
In an environment where humidity varies greatly, the humidity sensor 31 is disposed, was measured humidity stored in the memory unit 29, obtains a correction factor CF _h of humidity from the temperature determined from this value and the ultrasound, which formula ( The temperature t may be obtained by substituting in 3).
Reference numeral 28 denotes an arithmetic device, and 30 denotes a display device.

The present invention can also take the following configuration examples.
Ultrasound transmission / reception can be performed by transmission method in which transmission and reception sensors are arranged oppositely, transmission / reception separation type reflection method in which transmission and reception sensors are arranged separately, or transmission and reception sensors. The transmission / reception combined reflection method for transmitting and receiving the same wave may be used.
The ultrasonic sensor may focus on a single received waveform as a set of transmitting / receiving sensors, or may use a plurality of transmitting / receiving sensors and use information of a plurality of ultrasonic receiving signals. .
When there are a plurality of propagation paths, the temperature distribution image may be reconstructed by using a computer tomography (CT) reconstruction algorithm.

The ultrasonic propagation medium mainly targets air, but is not limited to gas but may be liquid or solid.
When the ultrasonic frequency is used in the air, the frequency band of 40 kHz is most often used, and it is most effective to use the present invention in this frequency band.
However, in principle, a low frequency close to a direct current to about 10 MHz considered as a practical upper limit can be targeted.
In solid or liquid, ultrasonic waves of 10 MHz or higher can also be used.

Although this system is mainly intended for temperature measurement, it is essentially characterized by the ultrasonic propagation time measurement method, and is applicable not only to temperature but also to measurement of airflow, distance, or humidity. Conceivable.
For example, two sets of transmission / reception systems with different ultrasonic wave transmission / reception directions are arranged in parallel, and information on the propagation time of each reception signal is used, thereby enabling simultaneous measurement of airflow and temperature.

INDUSTRIAL APPLICABILITY The present invention can be applied in various environments such as temperature monitoring using wall reflection in a room, temperature monitoring for air conditioning in a vehicle, and temperature monitoring of a long distance space in a greenhouse.
In particular, in temperature measurement in a vehicle, it is considered that there are many situations in which an object such as a wall and a sensor are close to each other, and it is considered that the effect can be further exhibited under such a situation.
Further, in the air conditioning in a vehicle, there is a concern that the temperature measured by a conventional sensor is a part of temperature information or poor responsiveness, but the present invention makes it possible to measure the space temperature with excellent responsiveness. .
Further, by changing the arrangement of the ultrasonic sensors and the number of sensors, it is possible to measure the temperature in a plurality of regions and to measure the temperature distribution, thereby providing a system that can support energy saving and comfortable space.
Application to temperature distribution measurement in boilers is also conceivable.
Furthermore, if the frequency to be used is selected as a low frequency, it can be expected to be applied to air conditioning in large indoor stadiums and halls.
Application to ultrasonic anemometers and indoor position recognition technology is also possible.

Claims (6)

The ultrasonic wave transmitted from the transmitter is received by the same or different receiver as the transmitter,
A method of calculating the propagation speed of ultrasonic waves by measuring the propagation time of propagation through the region to be measured, and measuring the temperature of the region,
Detection of the reception time by setting the envelope peak point on the reception side as the reference point of reception time, transmitting a positive phase wave for a predetermined time, and then transmitting an anti-phase wave with controlled amplitude and wave number A temperature measurement method using ultrasonic waves, characterized by improving accuracy and improving temperature measurement accuracy. Than the amplitude of the drive signal of positive phase waves, the temperature measuring method using ultrasound according to claim 1, wherein the direction of the amplitude of the drive signal of opposite phase wave is large. 2. The temperature measurement method using ultrasonic waves according to claim 1, wherein the wave number of the driving signal of the opposite phase wave is smaller than the wave number of the driving signal of the normal phase wave. The ultrasonic wave according to any one of claims 1 to 3, wherein the detection accuracy of the reception time is improved by detecting the time of the zero-cross point immediately after the received envelope peak time as a reference. Temperature measurement method using A transmitter that transmits ultrasonic waves, and a receiver that is the same as or different from the transmitter,
A temperature measurement device capable of calculating the propagation speed of ultrasonic waves by measuring the propagation time of propagation through the region to be measured, and measuring the temperature of the region,
After transmitting a normal phase wave for a predetermined time, an ultrasonic wave characterized by having a transmission control means for transmitting an antiphase wave whose amplitude and wave number can be controlled arbitrarily and an envelope peak time detection means A temperature measuring device. 6. The ultrasonic wave according to claim 5, further comprising a zero cross time detecting means for detecting a time of a zero cross point immediately after the envelope peak time using the envelope peak time detecting means as a reference. The temperature measuring device used.