JPS5928262B2 - ultrasonic anemometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic anemometer, and in particular to the calculation of wind speed.

As is well known, the ultrasonic anemometer utilizes the fact that the transmission time of sound waves changes depending on the wind speed. The first and second transducers TRx and TR-x are placed opposite to each other at intervals, and emit ultrasonic waves alternately from the first and second transducers TRx and TR-x over a short period of time. Waves are received alternately by TR-x and TRx, and the wind speed is measured from the propagation time of each sound wave.

That is, the transmission time of the sound wave in the arrow x direction is now tX) The transmission time in the arrow -x direction is -x, and the facing interval of the transducer is l)
When the speed of sound is c and the wind speed in the x direction is ri, the propagation time tx of the sound wave in the
= becomes -x=-... (1)c+ ric-ri.

And from now on, the wind speed will be = - (1 - -) ...... (2) 2tx
If we set −x and e/2 as a constant, we get =(−−−)・・・・・・・・・(3) when x is −
It is given by x.

However, if the calculation based on the wind speed derivation formula shown in equation (3) is conventionally performed using a reciprocal calculation circuit, the circuit becomes complicated and expensive, and the probability of failure also increases. The reliability of operation also decreases.

Therefore, conventionally, as shown in FIG. 2b, the oscillation period T of the emitted ultrasonic pulses P82 and P87 of the first and second transducers is set. (Second
(see figure a), create a sawtooth wave E8 with the same period as figure 2c.
The received signals PR' and PR of the second and first transducers are as follows.
7, the sampled transmission time Tx,t-o
The difference between the voltages Ex and E-, which are proportional to the wind speed, is determined to obtain an output proportional to the wind speed. Although this method contributes to the simplification of the structure and the reduction in cost, its output is equivalent to , and includes the sound velocity C which changes depending on the temperature of the measuring atmosphere as seen in the equation.

For this reason, when the measurement temperature range is, for example, from -10°C to +40°C, there is a drawback that a large measurement error of about 10% occurs, and if accurate measurement is required, please refer to (3) above.
It is necessary to use a complex arithmetic circuit based on formulas. The present invention creates an oscillation frequency output whose frequency changes in inverse proportion to the passage of time from the emission of a transmission wave to the emission of the next transmission wave, detects the frequency at the time of reception from this frequency output, and then By detecting the amount equivalent to the reciprocal of the time from the time of emission to the time of reception, and determining the wind speed from the difference in the amount in the forward and reverse directions, it is possible to accurately measure wind speed without being affected by the measurement temperature and atmosphere using a simple circuit. It is designed so that it can be measured.

Next, the present invention will be explained in detail with reference to the drawings. Third
The figure is a block system diagram of an embodiment of the present invention, FIG. 4 is a waveform diagram of each part of the circuit, FIG. 5 is an example circuit diagram of a sawtooth wave generator, and FIGS. 6 and 7 are diagrams of a voltage controlled oscillator. 2 is a circuit example diagram and a waveform diagram of each part of the circuit. FIG.

In Fig. 3, TRx and TR-o are the first and second transducers placed opposite each other at a constant interval e, and MOSC is the main oscillator, as shown in Fig. 4 A, b, c, d, e, and f. control pulse PG
Sends O, PGl, PG2, PG3, PG4 and PG5. POSC is a nozzleless oscillator, and the main oscillator MOS
From C to time T. Pulse PGO sent out every time (Fig. 4a)
) and controlled by the time T. Pulse P for excitation of the transducer every time. Send out. RA is a reception wave shaping circuit that amplifies and shapes the reception signal of the first or second transducer. SW is a transmission/reception changeover switch (electronic), which includes a first switch SWl consisting of fixed contacts A, b and their switching contact c, and a second switch SWl consisting of fixed contacts A2, b2 and their switching contact C2.
It consists of a switch SW2. Then, the transmission/reception changeover switch SW firstly switches the main oscillator MOSC's sending pulse PGl (fourth
T every 3T0 in synchronization with the pulse PGO (see Fig. 4a). Only switching contact piece C, c
2 is switched to the fixed contact A, a2 side, and the output pulse P of the pulse oscillator POSC. The first transducer TRx
In addition, a sound wave pulse PSl shown in FIG. 4g is transmitted toward the second transducer TR-. The second transducer TR receives the sound wave pulse PRl arriving after time t1 as shown in Fig. 4h.
It receives the wave as follows, converts it into an electric signal, and applies it to the reception wave shaping circuit RA, which amplifies and shapes it and sends it to the sawtooth wave generator SWG (described later) as a reception signal RSS1 (see Fig. 4, 1). )
Add as. Next, when the transmitting operation of the first transducer and the receiving operation of the second transducer are completed, the transmitter/receiver switch SW switches the main oscillator MOSC's sending pulse PG2 (the fourth
(see Figure C), the time T from said pulse PGl. T after every 3T0. Only switching contacts C, c'
is switched to the fixed contact B, b2 side, and the output pulse P of the pulse oscillator POSC. to the second transducer TR-, and a sound wave pulse PS toward the first transducer TRx.
2 (Fig. 4g) is transmitted. The first transducer TRx converts the sound wave pulse PR2 (see Fig. 4h) that has arrived after time T2 has elapsed into an electrical signal and applies it to the receiving wave shaping circuit RA.
A amplifies and shapes this and applies it to a sawtooth wave generator SWG, which will be described later, as a received signal RSS2 (see FIG. 4, 1). That is, in the above, time T in FIG. The first section M1 (
Hereinafter, this will be referred to as the first wave transmission/reception section. ), wave transmission and reception is performed from the first transducer TRx to the second transducer TR-o, and the next time T elapses. In section M2 (hereinafter referred to as the second transducer section), the second transducer TR. ．． TR?
x to the first transducer TR. After transmitting and receiving waves in the direction i, time T elapses in section M3. After that, the above-mentioned vortex operation is repeated cyclically, and the period M3 of stopping the wave transmission and reception is a time T based on fluctuations in the power supply voltage, etc., as will be described later. It is used as a frequency calibration interval for a variable frequency oscillator whose oscillation frequency changes in inverse proportion to the passage of time. Next, SWG is a sawtooth wave generator, which is formed from the various parts shown in FIG. 5, for example.

In FIG. 5, 0P1 is the first operational amplifier, Rl, R2
, R3 is a resistor, SW3 is a switch (electronic), 0R is an OR circuit, FFl is a flip-flop circuit, R4 is a resistor,
0P2 is the second operational amplifier, C is the integrating capacitor, and S
W4 is the switch (electronic), Es is the reference voltage, and ΔEs is the time T detected in the calibration interval M3 as described above.
. This sawtooth wave generator SWG has the following deviation voltage between the frequency of the variable frequency oscillator, which changes the oscillation frequency in inverse proportion to the passage of time, and the correct oscillation frequency (this will be explained in detail later). perform an action. First operational amplifier 0P
1 applies the sum of the frequency deviation voltage ΔEs and the reference voltage Es -(Fs+ΔE8) to the switch SW3. (Δ
Es is corrected every calibration interval M3). Furthermore, the flip-flop circuit FFl is connected to the first and second wave transmitting/receiving sections Ml, M2.
In this case, the main oscillator MOSC sends out pulse PG3 (fourth
d), that is, rises simultaneously with the transmission of pulse PGO (see Fig. 4a), and indicates the upper limit (TO?) of measurement time t1 or T2 in Fig. 4. Pulse arrival time T.

Pulse PG3 falling after elapsed time and output R of receiving wave shaping circuit RA
Controlled by SS1 or RSS2. Then, the output becomes H level at the falling edge of pulse PG3,
When RSS1 or RSS2 is input, it changes from H level to L level. Pulse PG6 in FIG. 4J, that is, the time interval is (T, -
TO) or (T2-TO) control pulse PG6 is sent out to control switch SW3. In addition, in the calibration interval M3, the pulse PG5 (see Fig. 4f) from the main oscillator MOSC via the OR circuit 0R, that is, the lower limit of the measurement time t1 or T2Z in Fig. 4 (T3〉7---π--) It is controlled by pulse PG5 and pulse PG3, which are sent out after a time T3 that is longer than the pulse arrival time to the other party's transducer indicating .

Then, the switch SW3 is controlled by sending out a pulse PG6 (see FIG. 4 j) whose time width is (T3-TO) from going to H level at the falling edge of pulse PG3 and going from H level to L level at the rising edge of pulse PG5. do. Also switch SW
4 is turned on by the sending pulse PG3 (see Figure 4 d) of the main oscillator MOSC, and the pulse PGO (see Figure 4 a) is turned on.
Time T from the sending of. Then, the input and output of the second operational amplifier 0P2 are short-circuited. (The charge in the integrating capacitor C is discharged.) Therefore, the time T until the pulse PG6 is sent out.
During this period, the output ESW of the second operational amplifier 0P1 is zero as shown in FIG. When it is turned on for (T3tO), the second operational amplifier 0P2 during this period is the sum of the reference voltage Es and the deviation voltage ΔEs - (
Es+ΔEs) is integrated. When the pulse PG6 disappears and the switch SW3 is turned off, the integrated voltage El, E2 or E3 at that time is held and then returned to zero as shown in FIG. 4k. Next, the circuit from the SOSC to the VCO forms a well-known phase-locked loop circuit, the so-called PLL circuit, and the above-mentioned time T by the above-mentioned sawtooth wave generator. A circuit that forms a variable frequency oscillator whose frequency changes in inverse proportion to the passage of time.
is a reference frequency oscillator (e.g. crystal type), T shown in dotted lines in FIG. 4e. The elapsed time T of the rise of the pulse PGO (see FIG. 4a), with the frequency change f being inversely proportional to the time elapsed between. The frequency F is proportional to the reciprocal of . oscillates. PD is a phase detector that performs phase detection of the output of the reference frequency oscillator SOSC and the output of the voltage controlled oscillator VCO, which will be described later. The LPF is a low frequency filter that removes unnecessary wave number components from the phase detection output and converts it into an average value voltage. SH is a sample and hold circuit which detects the time T from the rise of the pulse PGO by the sending pulse PG3 (see FIG. 4d) of the main oscillator MOSC. Only the output voltage E of the low frequency filter LPF is
fOl, that is, the oscillation frequency F. A voltage EfO corresponding to PG3 is sampled, and EfO is held by, for example, a capacitor during a period when PG3 is not present. ADD is an adder circuit, and as shown in Fig. 4m, the output voltage EfO of the sample and hold circuit SH is
and the output voltage Esw of the sawtooth wave generation circuit SWG described above.
Perform the addition of . (2) CO is a voltage controlled oscillator, and this circuit is formed from the various parts shown in FIG. 6, for example. In FIG. 6, CI is a constant current source, C1 is a capacitor charged by the constant current source, and EC is a voltage comparator. Compare.

WF is a waveform shaping circuit, SW5 is a switch (electronic),
The above waveform shaping circuit W is connected in parallel with the capacitor C.
On/off control is performed by the output of F. FF2 is a flip-flop circuit, and the voltage controlled oscillator consisting of the above-mentioned parts performs the following operations. When the input voltage EIN of the comparator EC is a constant voltage EfO as shown in FIG. 4m, the peak value of the terminal voltage ECl of the capacitor C1 is constant at EfO as shown in FIG. 7a. Therefore, the switch SW5 is turned on for a short time at a constant cycle by PG7 to discharge the charge of the capacitor C1, and the frequency of the output pulse PG8 of the flip-flop FF2 becomes constant. For example, if the value of the capacitor C1 is adjusted to make the output frequency of the flip-flop FF2 match the oscillation frequency FO described above (see Figure 4e), the voltage controlled oscillator (See Figure 4a) Time T starts from the rise of . Question number F until it passes. The oscillation frequency is accurately made constant by the PLL circuit configuration described above. And time T. After the elapse of time, the output ESW of the sawtooth wave generator SWG shown in FIG. 4k is added to the addition circuit ADD, and as the output voltage EIN of the addition circuit ADD gradually increases, the peak value of the terminal voltage of the capacitor C1 also increases to the value shown in FIG. 7a'. The period of the pulse PG7 sent out at each voltage comparison point becomes longer as shown in FIG. If the circuit constants such as the integration time constant of the sawtooth wave generator SWG are appropriately selected, the voltage controlled oscillator ■CO will be lower than the rising edge of the pulse PGO until T. It is possible to oscillate at a constant frequency F, which is proportional to the reciprocal of the time T, as shown in Fig. The output voltage Esw of the generator SWG is the received signal R
El, E by SSl, RSS2 or pulse PG3
2 or E3, each continues to oscillate at a frequency corresponding to the voltage when the voltage becomes constant, that is, a constant frequency proportional to the reciprocal of the reception arrival time (see Figure 4 e).
Time T comes to the next section. Only F again. Performs an oscillating operation. That is, the voltage controlled oscillator VCO calculates the time lapse Tl, t2 and the pulse PG until the second or first transducer receives the sound wave pulse from the first or second transducer.
Time lapse T3 from the sending of O until the calibration signal is added
Oscillation at a frequency proportional to the reciprocal of will continue until the next section. Next, in Figure 3, AG is andgade,
UDC is a preset table up-down counter (hereinafter referred to as a counter), REGl is the first register, and DA
l is a first digital-to-analog converter, REG2 is a second register for storing the frequency deviation voltage value, and DA2 is a second digital-to-analog converter for converting the digital value to an analog value. The circuit performs the following operations.

ANDGATE AG is the output pulse PG4 (see Figure 4e) from the main oscillator MOSC, that is, the control pulse PG for calibration.
5 (see Figure 4 f), the time width that continues until the pulse PGO is sent out in the next section is TO = (TO - T4).
With pulse PG4 as the gate control pulse, each section Ml
, M2, and M3, the output voltage of the voltage controlled oscillator VCO is applied to the counter UDC. The UDC is controlled by the sending pulses PGl and PG2 (see Fig. 4B and c) of the main oscillator MOSC, and first, the pulse P is output in the first transmission/reception section M1.
During the time TO determined by G4 (see FIG. 4e), the oscillation frequency f1 of FIG. 42 is added and counted as shown in FIG. In the second wave transmission/reception section M2, the time T is determined by the pulse PG4. By counting the oscillation frequency F2 in Figure 4e,
It is subtracted from the count number N in the first wave transmission/reception section M1. Therefore, the remaining amount ΔN■ of the counter UDC, where the subtraction value is now N2, will be, but as mentioned above, f1・F2
is proportional to the reciprocal of the time lapse Tl, t2 from the transmission of the sound wave pulse to the reception in the first and second transmission/reception sections Ml, M2, so the remaining amount ΔNv is where K, K2 are proportional coefficients, and ■ is The remaining amount of the counter UDC is proportional to the wind speed ■.

The remaining amount value ΔNv, which is proportional to this wind speed, is the second wave transmission/reception section M.
2, that is, at the rising edge of the control pulse PG2, is read out and written to the first register REGl, and the written amount is converted into an analog by the digital-to-analog converter DAl and outputted to the output terminal TOut as a voltage proportional to the wind speed. be done. Therefore, by measuring this value, the wind speed can be determined. Next, after one measurement in the first and second wave transmitting/receiving sections Ml and M2 is completed, the calibration section M3 is entered, and the variable frequency is adjusted based on the constant changes of the integrating capacitor etc. due to fluctuations in the power supply voltage, measurement atmosphere temperature, etc. Calibration of the oscillation frequency of the oscillation circuit is performed.

When the pulse PG2 from the main oscillator MOSC falls, which indicates the end of the second transmission/reception period M2, the counter UDC displays the calibration data Pd, that is, the voltage at the time of sending the control pulse PG5 (see Fig. 4 f) from the MOSC. Controlled oscillator VCO
The correct oscillation frequency of 8s is transmitted from the main oscillator MOSC by the time width T of the control pulse PG4 (see Figure 4e). I counted only T. Data N3S, which is equal to Xf3S, is preset to a negative value. And control pulse PG4 is AND gate A
When applied as a gate pulse to G, the counter UDC
performs an operation of counting the output frequency F3 (see FIG. 4') of the voltage controlled oscillator VCO for a time TO and adding it to the preset value -N3S. Here, assuming that there is no change in the oscillation frequency of the voltage controlled oscillator ■CO after time T3 has elapsed due to fluctuations in the ambient temperature, etc., the counter UD
The remaining amount ΔNs of C is zero, and if there is a change, ΔNs
s will be the positive or negative value of the difference between the correct frequency F3S and F3, which will be stored in the UDC. Then, when the main oscillator MOSC enters the first wave transmitting/receiving section M1 again and the pulse PGl (see Figure 4b) is sent out, this content is read out and written to the second register REG2, and digital-to-analog conversion is performed. The device DA2 is analogized and the frequency deviation voltage ΔE is
s is applied to the sawtooth wave generator SWG shown in FIG. Then, when ΔEs has negative polarity, Es - ΔEs is added to the second operational amplifier 0P2, and when ΔEs is positive, the voltage of Es + ΔEs is added to 0P2, and the rising slope of the voltage is adjusted according to ΔEs to correct the oscillation frequency. The frequency is automatically corrected to become F38. Therefore, correct reciprocal calculation is possible. Therefore, by repeating the above series of operations, changes in wind speed can be continuously and accurately measured. The present invention has been described above with reference to one embodiment. However, when high measurement accuracy is not required, or when the influence of fluctuations in the power supply voltage and ambient temperature is negligible, the adder circuit AD shown in FIG.
If the input voltage EfO of D is supplied by a constant voltage power supply, there is no need to adopt a phase-locked loop circuit configuration, and the circuit can be greatly simplified.

Furthermore, in this case, the calibration circuit can be omitted, so the circuit configuration can be further simplified. In addition, in the above example, the wind speed was calibrated every time the wind speed was measured, but since the changes in the circuit constants are not sudden,
Calibration may be performed approximately once every 100 times.
As is clear from the above description, the present invention provides a variable frequency oscillation circuit in which the time versus frequency change characteristic is set so as to extract the reciprocal of the propagation time of sound waves in the forward and reverse directions between transducers facing each other at regular intervals. and detect the reciprocal of the time from the transmission of the sound wave to the reception of the sound wave from the output frequency of the variable oscillation circuit when the received signal arrives, and from the first transducer to the second transducer and the second transducer. The wind speed is determined from the difference in the reciprocal of the transmission time when the sound wave is transmitted from the first transducer to the first transducer.

Therefore, unlike conventional ultrasonic anemometers that determine wind speed by determining the difference in voltage proportional to transmission time, there is no error caused by the measurement atmosphere temperature. In addition, the present invention can be constructed more easily and inexpensively than the traditional method of calculating the reciprocal of the transmission time using a reciprocal calculation circuit. This is done by using a frequency output that changes in inverse proportion to the elapsed time, and in order to achieve this, the frequency changes inversely proportional to the elapsed time from the emission time of one transmission wave to the emission time of the next transmission wave. In order to avoid the frequency at the time of the first transmission wave becoming infinite when obtaining the characteristics, the oscillator is made to match the above frequency change characteristics only within the required measurement time period. It was only after the idea of being able to find the reciprocal value of the time from the emission of the transmitted wave until the arrival of the received wave was created.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of an ultrasonic anemometer, Fig. 2 is a waveform diagram for explaining the wind speed calculation of a conventional device, Fig. 3 is a block system diagram of an embodiment of the present invention, and Fig. 4 is its diagram. Waveform diagrams of various parts of the circuit, Figure 5 is a circuit example diagram of a sawtooth wave generator used in the present invention, Figure 6 is a circuit diagram of a voltage controlled oscillator used in the present invention, and Figure 7 is the circuit. It is a waveform diagram of each part.

Claims (1)

[Claims] 1. From the difference in the propagation time of sound waves in the forward and reverse directions between the first and second transducers, which are arranged opposite to each other with a constant interval,
In an ultrasonic anemometer designed to know the wind speed, it is controlled by an input indicating the emission of the transmitted wave, an input indicating the upper limit of the measurement time period, and an input indicating the arrival of the received wave. It oscillates at a constant frequency up to the upper limit, and then the oscillation frequency changes in inverse proportion to the passage of time.
Next, a variable frequency oscillator circuit that stops changing the oscillation frequency when the received wave arrives and continues to oscillate at a constant oscillation frequency from then on until the next transmitted wave is emitted, and a variable frequency oscillation circuit that receives the transmitted wave of the first transducer. The oscillation frequency of the variable frequency oscillation circuit based on the output of the second transducer is added and counted for a certain period of time from the time of reception, and from the above added count value, when the first transducer receives based on the second transducer. An ultrasonic anemometer characterized by comprising a circuit that subtracts and counts the oscillation frequency of the variable frequency oscillation circuit and calculates the wind speed from the difference between the two counted values. 2 Calibration of the variable frequency oscillator circuit Add and count the oscillation frequency when the signal arrives for a certain period of time, find the difference between this and the preset value, control the variable frequency oscillator circuit based on this, and calibrate the oscillation frequency. The ultrasonic anemometer according to claim 1, further comprising an additional circuit.