JP3616836B2 - Wind speed measuring method and apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a wind speed measuring method and apparatus for measuring the velocity of a gas by detecting the influence of a thermistor heated to a constant temperature from a wind flow, and more particularly to a measuring method and apparatus for a micro wind speed region.
[0002]
[Prior art]
In recent years, a thermistor type anemometer using a thermistor as a detection element has been used instead of a hot wire type anemometer. This is because the thermistor type is smaller and more punctate than the hot-wire type, so it does not disturb the airflow and has less directivity, so it can be measured accurately, especially in the area of low wind speed. Because.
[0003]
However, since such a thermistor anemometer also uses the thermistor to generate heat, the output from the constant temperature circuit is similar to the output from the bridge in the hot wire anemometer, as shown by the curve in FIG. This is a non-linear characteristic that substantially follows the KING equation “proportional to the 1/4 power of the wind speed”.
[0004]
In order to digitally display such characteristics, a linearizer is required. As a linearization method, generally, a polygonal line approximation method or a table lookup method for sequentially accessing data from a lookup table in a ROM is used. Although it is used, it is more economical to perform numerical conversion by the direct table look-up method in which accessed data is directly sent to a subsequent display device or the like for characteristics with strong non-linearity.
[0005]
As shown in FIG. 6, the linearization method using the direct table look-up method is such that the output voltage of the constant temperature circuit 12 to which the wind speed detection thermistor 11 is connected is input to the A / D converter 15, and the A / D converter 15 The binary output value from the D converter 15 is input as the ROM address value of the ROM 16. As shown in FIG. 5, when the ROM address corresponding to the output voltage a is accessed in the ROM 16, the corresponding ROM data is output from the lookup table to the display unit 17 as the wind speed value b 'on the reference characteristic. . At this time, the wind speed characteristic value from which the influence of self-convection due to self-heating of the thermistor is removed is input to the lookup table. (Fig. 5 line segment aq '→ q'b')
The measurement value conversion method using such a linearization method has an advantage that the circuit configuration is simple and can be converted at high speed.
[0006]
[Problems to be solved by the invention]
However, the conventional method has the following problems.
The conventional measurement method using the circuit shown in FIG. 6 uses the output voltage as a ROM address and the wind speed value on the voltage-wind speed characteristic from which the self-convection component due to self-heating as shown by the dashed line in FIG. 5 is removed. Are stored in the ROM lookup table. For this reason, when the output voltage from the constant temperature circuit has a strong non-linearity characteristic such as a 1/4 power characteristic, the change in the wind speed with respect to the change in the output voltage becomes very large in the region where the output voltage is large, When this is applied to the ROM lookup table, the ROM data value obtained for one ROM address change becomes a large error value including several wind speed values. On the other hand, in the region where the output voltage is small, the change in the wind speed with respect to the change in the output voltage becomes very small. When this is applied to the ROM look-up table, the value of the ROM data obtained for one ROM address change is output. It cannot respond to the voltage change, and the same wind speed value is obtained. As described above, there is a drawback that the accuracy is lowered in either region. Further, if it is attempted to obtain a fine wind speed value in order to prevent a discontinuous phenomenon in a region having a large slope, it is necessary to greatly increase the resolution of the A / D converter and set the output voltage finely, thereby reducing the look. As the up-table increases, the ROM requires a large memory capacity and suddenly loses economic efficiency.
[0007]
Further, in the measurement of the slight wind speed region, it is necessary to remove the influence of self-convection due to self-heating. This is done by performing a complicated heat conduction simulation calculation considering the mounting state of the thermistor. Characteristics as indicated by the broken line must be obtained, which is not easy in terms of complexity and accuracy.
[0008]
The reason for this is as follows.
In FIG. 5, an arbitrary output voltage a corresponds to a point p on an actual measurement characteristic including self-convection (hereinafter referred to as an actual measurement characteristic) indicated by a solid line in FIG. Hereinafter, it corresponds to the point q ′. Here, the point p on the actually measured characteristic and the point p for the output voltage a having the same characteristic share the line segment pq ′ and the line segment bb ′ as the wind speed difference with respect to the removal characteristic. However, this is a physical quantity called wind speed, and cannot be directly canceled by a differential operation called “comparison” like a bias of an electric circuit. Therefore, in order to obtain the wind speed from the output voltage a, the wind speed value b ′ must be obtained from the point q ′ on the removal characteristic indicated by the broken line in FIG. 5 by complicated simulation calculation.
[0009]
The present invention has been made in order to solve such conventional drawbacks, and the object of the present invention is to use the characteristics including self-convection without using complicated simulation calculation. An object of the present invention is to provide a thermistor wind speed measuring method and apparatus having high accuracy by removing components and performing linearization at the same time.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned object, a method and apparatus for measuring wind speed according to the present invention provides an output voltage from a self-heated thermistor for detecting wind speed, which is changed by wind flow, and an address scan from a CPU to a ROM look-up table. a voltage D / a conversion of the ROM data to be is been made to the measurement points when the respective voltages are compared are matched by the comparator,
The self-heating temperature of the thermistor for wind speed detection by the constant temperature circuit is set near the lowest temperature in the negative resistance region,
A sample and hold circuit is connected between the constant temperature circuit and the comparator. The look-up table includes a wind speed value as a ROM address, and includes the influence of self-convection due to thermistor self-heating. The reference voltage as it is is stored as the data of the ROM address,
An address scan to the lookup table is performed for all addresses, and during that time period, the output from the constant temperature circuit is held,
In accordance with a coincidence signal input from the comparator via the CPU interface, the ROM address is output as a digital wind speed value via the CPU accumulator immediately after all addresses are scanned. It is.
[0011]
[Action]
The wind speed measuring method and apparatus according to the present invention having the above configuration uses the wind speed value of the required number of digits as the ROM address and the actually measured voltage corresponding to the wind speed value as the ROM data (the line segment bp → pa). If the inherent measurement characteristics shown for the wind flow are used as a reference, the unknown wind speed input is also on the same characteristics, the self-convection component is naturally removed, and complicated simulation calculation is unnecessary.
[0012]
The reason for this is as follows.
In FIG. 5, an arbitrary wind speed b corresponds to the point p on the measured characteristic indicated by the solid line and corresponds to the point q on the removal characteristic indicated by the broken line. Here, the point p on the actual measurement characteristic and the point p for the wind speed input b having the same characteristic share the line segment pq and the line segment ac as the voltage difference with respect to the removal characteristic. However, this is a physical quantity called voltage, and it is obvious that it corresponds to the bias of the electric circuit and is directly canceled by the difference operation of “comparison”. Therefore, in order to obtain the voltage from the wind speed input, even if the wind speed value b is not obtained from the point q on the removal characteristic indicated by the broken line in FIG. 5 by complicated simulation calculation, the self-convection is naturally removed even on the actual measurement characteristic. The
[0013]
Further, since the address scan of the ROM moves on the actual measurement characteristic, the comparison and coincidence operation with the unknown wind speed input having the same characteristic is naturally a linearization operation. Further, since the ROM address representing the wind speed value is scanned, the wind speed value does not become discontinuous in the region where the characteristic gradient is large, and the resolution is D / A converter and analog in the region where the characteristic gradient is small. Since the resolution is increased by the comparator, ROM addresses representing wind speed values rarely overlap. Thus, it is possible to provide a measurement method and apparatus that can solve all of the conventional drawbacks.
[0014]
【Example】
Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 4 is a perspective view of a thermistor wind speed sensor / probe showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a self-heated thermistor for detecting the wind speed, out of two small thermistors with uniform characteristics welded to stainless steel columns 22, 22 ', 23, 23' standing upright on the insulating base 21. Reference numeral 8 denotes a temperature detection thermistor which is not self-heated.
[0015]
These thermistors 1 and 8 are of axial lead type with a size of φ0.9 mm × 1.2 mm, and R (25 ° C.) = 5.46 kΩ and B constant (0/100 ° C.) = 3390K. The wind speed detection thermistor 1 is connected between the support posts 22 and 22 'by a long lead wire, and the temperature detection thermistor 8 is separated from the wind speed detection thermistor 1 so as not to disturb the air flow, and slightly below the support 23, 23 'is connected with a short lead wire.
[0016]
As shown in FIG. 3A, the wind speed detecting thermistor 1 is connected to a constant temperature circuit 2 including an operational amplifier and a transistor. Here, the operational amplifier is OP-07, the transistor is 2SC794, R ₁ = 1.5 kΩ, R ₂ = 46.92 kΩ, R ₃ = 39Ω, and Vcc = 12V.
[0017]
The operation of this circuit is such that a voltage difference corresponding to a change in resistance value of the wind speed detecting thermistor 1 that changes depending on the flow of wind deviates from a thermistor 1 and resistors R _{1 to} R ₃ via an operational amplifier and a transistor. Feedback is applied as power, the self-heating amount of the thermistor 1 for detecting the wind speed is changed, and the resistance value is kept constant, so that the operation is constant temperature. is there.
[0018]
With such operation and circuit constants, the operating temperature of the wind speed detecting thermistor 1 is close to the minimum temperature in the negative resistance region in the voltage-current characteristics of the wind speed detecting thermistor 1 as shown in FIG. Set to ° C. This temperature is selected so that the wind speed sensitivity on the constant temperature operating line intersecting the voltage-current characteristics is maximized while keeping the influence of self-convection as small as possible.
[0019]
Next, the wind speed measuring method of the present invention will be described with reference to FIG. In the figure, outputs from the wind speed detecting thermistor 1 and the constant temperature circuit 2 configured as shown in FIG. 3A are input to the sample and hold circuit 3.
[0020]
On the other hand, the microcomputer 6 (TMP47P400VN, Toshiba 4-bit CMOS) incorporates an 8-bit one-time P-ROM. A ROM address having a width of 400 corresponding to a wind speed of 0 to 2.00 m / s is assigned to this ROM with an offset address added, and the data area of the 8-bit width ROM is shown in FIG. In accordance with actual measurement characteristics including self-convection indicated by a solid line, a reference voltage corresponding to the wind speed is stored with a data length of 12 bits across 2 bytes. Hereinafter, the ROM lookup table regarding the wind speed is referred to as a wind speed map area.
[0021]
The CPU (central processing unit) of the microcomputer 6 sequentially scans the address of the wind speed map area corresponding to the wind speed value according to the program stored in advance in the ROM, and each time the digital value of the reference voltage is stored in the accumulator. Through the output terminal IO ₁ having a 12-bit width to the D / A converter 5. At this time, since the accumulator of the CPU of the microcomputer 6 is 4 bits, the ROM data is sent to the IO ₁ in three times, and 12-bit wind speed value data is formed.
[0022]
The output of the D / A converter 5 is input to the comparator 4 and compared with the output of the sample and hold circuit 3. When the unknown wind speed voltage matches the reference voltage in the ROM, a match signal is output from the comparator 4 and input to the input terminal IO ₂ of the microcomputer 6. Based on the signal, the CPU stores the first address of the ROM address for two addresses at that time in a temporary register or RAM as a wind speed value, and immediately after all addresses in the wind speed map area are scanned, the value is stored in an accumulator. Excluding the offset address, a half operation is performed, and then sent to the 3-digit LCD display 7 from the output terminal IO ₄ .
[0023]
Here, while the CPU scans the address of the wind speed map area, if the output from the constant temperature circuit 2 changes, accurate measurement cannot be performed. Therefore, as shown in FIG. All addresses in the area are scanned, and during that time period, the output from the constant temperature circuit 2 is programmed to be sampled and held by the sample and hold circuit 3, and the control signal is output from the output terminal IO _3. Is output.
[0024]
The measured values in FIG. 2 (a) are examples of operation at a relatively low speed. When one access time is 0.7 ms, a sample and hold time of 280 ms is minimum for one measurement cycle 200 times and 400 bytes of access. However, in practice, it was set to 281.4 ms with a margin for one access time before and after. Then, during one access time added at the end, the ROM address as the wind speed value is subjected to the above operation by the accumulator from the register or RAM and sent to the output terminal IO ₄ .
In general, the input is sampled and held only until the coincidence signal is output from the comparator 4, and a measurement method in which the measurement time is short at a low wind speed and the measurement time is long at a strong wind speed is conceivable. However, in the present invention, the measurement time is made constant as described above, and the subsequent data processing is easily performed.
[0025]
Here, the result of measuring the measurement accuracy according to the present example by the wind tunnel test is shown in FIG. The wind speed measurement range was 0 to 2.00 m / s, and the air temperature was 25 ° C. According to this, even in the minute wind speed region, the error is about ± 0.5% (± 1 digit) of the full scale, and an accuracy that is hardly found in a commercial anemometer can be realized.
[0026]
The reason why high-accuracy and stable measurement can be realized in this way is that linearization is performed accurately by removing the influence of self-convection. In order to confirm this point, the zero point drift of the display was within ± 0.5% (± 1 digit) regardless of the direction of the wind speed sensor / probe shown in FIG. This result shows that the self-convection fluctuations resulting from differences in heat dissipation due to sensor probe asymmetry are almost eliminated.
[0027]
Further, in the linearization method using the direct table look-up method shown in FIG. 6 as a conventional example, the resolution is increased 10 times with respect to the measurement of 0 to 2.00 m / s, and 2000 bytes of data is stored in the ROM. Otherwise, discontinuity and duplication of wind speed values cannot be reduced to an inconspicuous level, whereas in this embodiment, only 400 bytes of address correspond to a 12-bit data length without play. Although it has a sufficient resolution and uses a very small memory capacity, there is no discontinuity or overlap of wind speed values as described above.
[0028]
Further, in the conventional method, the data from which the self-convection component is removed is stored in the ROM by complicated simulation calculation. However, in this embodiment, it is only necessary to store the actual measurement data including the self-convection component. So there is no need for complicated simulation calculations.
[0029]
From the above results, the wind speed measuring method according to the present embodiment was measured by removing the components naturally while using the characteristics including the self-convection component as a standard, and with a small microcomputer of 4 bits and a small ROM capacity. Clearly, accurate measurements without discontinuities or overlaps are possible.
[0030]
In the present invention, the thermistor is a temperature-sensitive element, and the measured value changes in the same manner as the change in the wind speed due to a change in the air temperature, causing an error. As means for compensating for this, in this embodiment, the temperature detection thermistor 8 shown in FIG. 4 is connected to the temperature conversion circuit 9 as shown in FIG. Since the temperature dependency in this embodiment is linear at any wind speed, the temperature conversion circuit 9 is a simple linear amplifier, and its output corresponds to the temperature dependency of the reference voltage terminal Vref of the D / A converter 5. The temperature dependence is compensated. The means for compensating the temperature is not limited to the embodiment, and various means such as compensating the output of the constant temperature circuit 2 using an amplifier whose amplification degree changes according to the resistance of the temperature detection thermistor 8. Is also possible.
[0031]
The present invention is not limited to the above embodiments. In this embodiment, an axial lead thermistor is used as the wind speed detecting and temperature detecting thermistor, but a radial lead thermistor may be used to make it non-directional. Moreover, the attachment of the thermistor for detecting the wind speed to the support is not limited to the vertical direction, and may be in the horizontal direction. Further, although a microcomputer incorporating a one-time P-ROM is used, a microcomputer incorporating a mask-ROM may be used.
[0032]
【The invention's effect】
As described in detail above, according to the present invention, the complicated simulation calculation for eliminating the influence of self-convection due to self-heating is not performed, and the measurement result excluding the self-convection component is naturally obtained in a linearized state. It is possible to perform accurate measurement without discontinuity or overlap of measured wind speed values. Further, since the ROM capacity for that purpose is very small, it is possible to realize a highly accurate wind speed measuring method and apparatus even in the micro wind speed region with very simple hardware and software.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a wind speed measuring circuit according to the present invention.
FIG. 2 is a diagram showing an embodiment of the present invention.
(A) is an operation diagram of the sample and hold circuit,
(B) is a wind tunnel test measurement result figure.
FIG. 3 is a diagram showing an embodiment of the present invention.
(A) is a circuit diagram of a constant temperature circuit,
(B) is a current-voltage characteristic diagram of a thermistor for detecting wind speed.
FIG. 4 is a perspective view of a general thermistor wind speed sensor / probe according to an embodiment of the present invention.
FIG. 5 is a wind speed-voltage characteristic diagram of a wind speed detecting thermistor used in the embodiment of the present invention and the conventional example.
FIG. 6 is a diagram showing a conventional example, and is a configuration diagram of a wind speed measuring circuit by a table lookup method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Thermistor for wind speed detection 2 ... Constant temperature circuit 3 ... Sample & hold circuit 4 ... Comparator 5 ... D / A converter 6 ... Microcomputer 7 ... Display 8 ... Thermistor for temperature detection 9. Temperature converter circuit

Claims (2)

The output voltage from the self-heated wind speed detection thermistor that changes depending on the wind flow is compared with the D / A converted voltage of the ROM data accessed by the address scan from the CPU to the ROM lookup table. Is a wind speed measuring method in which each voltage is matched, and the self-heating temperature of the thermistor for detecting the wind speed by a constant temperature circuit is set near the lowest temperature in the negative resistance region, A sample and hold circuit is connected between the constant temperature circuit and the comparator, and the wind speed value is a ROM address in the lookup table, and the influence of self convection due to thermistor self heating is included. Is stored as the data of the ROM address, and the address scan to the lookup table is performed. The output from the constant temperature circuit is held during that time period, and the ROM address is immediately after all addresses are scanned by the coincidence signal input from the comparator through the CPU interface. A wind speed measuring method comprising means for outputting a digital wind speed value via an accumulator of a CPU. The output voltage from the self-heated wind speed detection thermistor that changes depending on the wind flow is compared with the D / A converted voltage of the ROM data accessed by the address scan from the CPU to the ROM lookup table. Is a wind speed measuring device having a measurement point when the respective voltages match, and the self-heating temperature of the thermistor for detecting wind speed by a constant temperature circuit is set near the lowest temperature in the negative resistance region, A sample and hold circuit is connected between the constant temperature circuit and the comparator, and the wind speed value is a ROM address in the lookup table, and the influence of self convection due to thermistor self heating is included. Is stored as the data of the ROM address, and the address scan to the lookup table is performed. The output from the constant temperature circuit is held during that time period, and the ROM address is immediately after all addresses are scanned by the coincidence signal input from the comparator through the CPU interface. A wind speed measuring apparatus comprising means for outputting a digital wind speed value via an accumulator of a CPU.

Images