JP2002174639A - Tidal current measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tidal current measuring device capable of constantly measuring the current speed and the bearing of a tidal current near the water surface even when the tide level changes. SOLUTION: The measuring device is provided with a receiver for water surface 27 amplifying an electric signal based upon an ultrasonic wave reflected by the water surface by an amplification degree weaker than four receivers 14, 18, 21, and 24 respectively amplifying four electric signals outputted by a transducer 8 installed on a sea floor, emitting four ultrasonic waves obliquely upward in four directions, receiving four ultrasonic waves reflected by measurement mediums in the sea, and converting them into the electric signals, and a counter 32 measuring time by a predetermined frequency between a transmission command to an oscillator 2 of an arithmetic control part 1 and receiving of the electric signal by the water surface receiver 27. The arithmetic control part 1 calculates a distance from the transducer 8 to the directly above water surface on the basis of the time measured by the counter 32, and a sampling timing signal corresponding to the distance is outputted to three Doppler shift detection circuits 15, 19, 22, and 25 measuring a Doppler frequency shift between a frequency of a signal of the oscillator and frequencies of the electric signals outputted from each receiver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tidal current measuring device for measuring a flow velocity and an azimuth near the sea surface using ultrasonic waves.

[0002]

2. Description of the Related Art FIG.
FIG. 5 is a block diagram showing the configuration of a conventional tidal current measuring device disclosed in a document issued by the Society for Ocean Acoustic Research in 1984, and FIG. 5 is a timing chart of signals at various parts of the tidal current measuring device. In the figure, 1 is an arithmetic control unit that outputs a transmission command and a sampling timing signal and calculates the velocity v of a tidal current, etc., 2 is an oscillator that oscillates a burst signal based on a transmission command from the arithmetic control unit 1, 3, Reference numerals 4, 5, and 6 denote power amplifiers for amplifying the burst signal output from the oscillator 2 to a certain level, 7, 11, 12, and 13 denote power amplifiers 3,
The amplified signals of 4, 5, and 6 are transmitted to the transmitter / receiver 8, and the electric signals from the transmitter / receiver 8 are received and the receivers 14, 18, 2
A transmission / reception switch for switching transmission to 1, 24, 9 is a medium to be measured in seawater, and 10 is a surface of seawater.

The transducer 8 has a structure in which four transducer elements are mounted in four directions. The distances from these four transducer elements to the water surface 10 are the same distances but only in different directions. 15, 19, 22, 2
5 is the frequency of the burst signal of the oscillator 2 and the receivers 14, 1
A Doppler shift detector for measuring the Doppler frequency shift with respect to the frequency of the signal received at 8, 21, 24;
20, 23, 26 are Doppler shift detectors 15, 19,
An A / D converter that converts the analog signal of the Doppler frequency shift detected by 22, 22 into a digital signal and inputs the digital signal to the arithmetic and control unit 1, and 17 is a display for displaying the flow velocity v and direction of the tidal current.

[0004] The operation of the conventional tidal current measuring device configured as described above will be described. The oscillator 2 oscillates a burst signal based on the transmission command shown in FIG. The oscillation signal of this oscillator 2 is
After being amplified to a certain level by 4, 5, and 6 (b in FIG. 5 shows the output of the power amplifier 3), the transmission / reception switch 7, 11, 1
2 and 13, the electric signal is applied to the transducer 8 installed on the sea floor, and the electric signal is converted into an ultrasonic signal.
From above, and is sent out in four directions to the medium 9 to be measured in seawater.

The oscillation signal of the oscillator 2 passes through power amplifiers 3, 4, 5, 6 and transmission / reception switches 7, 11, 12, 13 and receivers 14, 18, 21, 24, and a Doppler shift detection circuit. 15, 19, 22, and 25. 4
The ultrasonic signal transmitted in the direction is reflected by the fine particles included in the measured medium 9 and received by the transducer 8,
Converted to electrical signals. This electric signal is transmitted and received by the duplexer 7,
The receivers 14, 18, 21,
The signal is amplified to a certain level at 24 and input to the Doppler shift detection circuits 15, 19, 22, and 25 (C in FIG. 5 shows the output of the receiver 14).

The Doppler shift detection circuits 15, 19, 2
In steps 2 and 25, the Doppler frequency shift between the frequency of the oscillation signal of the oscillator 2 and the frequency of the received electric signal is measured. At this time, a sampling timing signal is transmitted from the arithmetic and control unit 1 as shown in FIG. 5D, and the Doppler shift detection circuits 15, 19, 22, and 25 determine the Doppler frequency shift by a predetermined sampling timing signal. Select and take out at the timing. The extracted Doppler frequency shift is converted from an analog signal to a digital signal by the A / D converters 16, 20, 23, and 26 and input to the arithmetic and control unit 1. Here, the velocity of the tidal current is v, the frequency of the transmission wave is f ₀ , the sound velocity of the medium to be measured is C, the angle between the traveling direction of the ultrasonic beam and the flow is θ, and the reception frequency is _fr
Then, since f _r = f ₀ × (1 + 2 v · cos θ / C), the Doppler frequency shift f _d is as follows. f _d = _fr −f ₀ = f ₀ × 2v · cos θ / C

Accordingly, an equation for obtaining the velocity v of the tidal current is as follows by expanding the above equation. v = f _d · C / 2 · f ₀ · cos θ Here, cos θ is an angle between the traveling direction of the ultrasonic beam and the flow, that is, the launch angle of the ultrasonic wave, and is predetermined, and C is the medium to be measured. , Determined by water temperature and salinity, and usually corrected by measuring water temperature. Therefore,
The arithmetic control unit 1 can calculate the velocity of the tidal current by calculating v. In this case, for example, when it is desired to measure the flow velocity of the layer at a height D directly above the transducer 8, the reflected signal from a distance away from the transducer 8 is converted to a sample timing signal (t = 2D / C). (Cos θ) must be sampled and taken out.

[0008] The reason is that if it is attempted to measure the flow velocity of a layer located at a distance D (m) directly above the transducer 8 with respect to the transducer 8, the ultrasonic waves are emitted in the inclined θ direction as shown in FIG. Therefore, it is sufficient to sample the location of the propagation path l (m). Then, in the ΔABD shown in FIG. 2, cos θ = D / l (1) If the sound velocity in water is C (m / S), the sound is emitted from A The time when the reflected ultrasonic wave is reflected at point B and returns to point A again is t (se
Assuming that c), the propagation path is reciprocating, so that 2l = Ct (2) l = 1/2 · Ct ... (3) By substituting equation (3) into equation (1), cos θ = D · 2 / Ct (4) Equation (4) This is because t = 2 · D / C · cos θ (5) In addition, as shown in FIG.
If the depth of the water surface is d (m), the sampling point will always be below the water surface and can be measured if d> D, but if d ≦ D, the sampling point will be on the water surface and measurement is impossible. Becomes

Therefore, when measuring the flow velocity of the tidal current near the water surface of the sea, the emission angle θ of the tidal sound wave of the transducer 8 is determined, and if the lowest tide is known, the tidal current near the water surface at the lowest tide is determined. By performing sampling at the timing of the sampling timing signal (t = 2D / C · cos θ), each Doppler shift detection circuit 15, 1 can be measured.
The arithmetic and control unit 1 calculates the flow velocity v of each tidal flow based on the Doppler frequency shift measured by 9, 22, and 25, converts the flow velocity into a vector flow velocity in four directions, and further calculates the flow velocity v of the tidal flow combined by the calculation. The azimuths are obtained, and these are displayed on the display 17.

[0010]

In the conventional tidal current measuring device as described above, when measuring the tidal current near the surface of the sea which is important for navigation of a ship, etc., when the tide level of the sea does not fluctuate so much, With a preset launch angle of 8, the transducer 8
Since the distance from the surface to the tide level just below the water surface to be measured is also fixed, the Doppler shift detection circuits 15, 19, 2
By sampling and extracting the Doppler frequency shift measured by the second and the 25th at the timing of the predetermined sampling timing signal, the flow velocity of the tidal current just below the water surface can be measured. For example, when the sea level is about 2m, it is set so that the tidal current near the water surface can be measured at the lowest tide of the sea. At the highest tide, the tidal current 2m below the water surface will be measured. There is a disadvantage that it is impossible to measure the tidal current near the water surface, and there is a problem that a technically satisfactory one cannot be obtained. The present invention has been made to solve such a problem, and an object of the present invention is to provide a tidal current measuring device capable of always measuring the velocity and direction of the tidal current near the water surface even when the tide level of the sea changes.

[0011]

According to the present invention, there is provided a power flow measuring device comprising: an oscillator for oscillating an electric signal of a predetermined frequency based on a transmission command; and at least three oscillators installed on the sea floor based on the electric signal of the oscillator. A transmitter / receiver that emits ultrasonic waves obliquely upward in three directions and receives three ultrasonic waves reflected by a measuring medium in the sea and converts them into electric signals, and three electric signals output by the transmitter / receivers And a receiver for amplifying the respective signals, and measuring the Doppler frequency shift between the frequency of the oscillator signal and the frequency of the electric signal output from each receiver.
A Doppler shift detection circuit and a transmission command are output to an oscillator, and a predetermined sampling timing signal is output to each Doppler shift detection circuit, and each tidal current is detected based on the Doppler frequency shift extracted at a predetermined timing. After calculating the flow velocity and converting it into a vector flow velocity in three directions, the flow rate measuring apparatus further comprises a calculation control unit for calculating the flow velocity and direction of the tidal current vector-combined by the calculation. Amplify one of the signals,
The amplification degree is weaker than the two receivers, the water surface receiver which amplifies the electric signal based on the ultrasonic wave reflected on the water surface, the transmission command to the oscillator of the arithmetic control unit, and the water surface receiver receives the electric signal And a counter that measures the time between the time and the time at a predetermined frequency, the arithmetic control unit calculates the distance from the transducer to the water surface immediately above based on the time measured by the counter, It is configured to output a sampling timing signal corresponding to the distance to the three Doppler shift detection circuits.

In the present invention, at least three ultrasonic waves which are installed on the sea floor and are emitted obliquely upward in three directions are received, and the three ultrasonic waves reflected by the underwater measuring medium are received and converted into electric signals. The amplification degree is weaker than the three receivers which respectively amplify the three electric signals output by the transmitting / receiving transducer,
A receiver for the water surface that amplifies an electric signal based on the ultrasonic wave reflected on the water surface, and a time between a transmission command to the oscillator of the arithmetic control unit and a time when the receiver for the water surface receives the electric signal is a predetermined frequency. The arithmetic and control unit calculates the distance from the transmitter / receiver to the water surface immediately above based on the time measured by the counter, and calculates a sampling timing signal corresponding to the distance to the frequency of the oscillator signal. And the frequency of the electric signal output from each receiver is output to three Doppler shift detection circuits that measure the Doppler shift, so that even if the sea tide level to be measured changes, the operational amplifier can Changes in the sea that greatly affect the ship's operation based on the Doppler frequency shift extracted from the Doppler shift detection circuit at the timing of the sample timing signal The flow rate of the tidal currents near the water surface tide can be accurately calculated, and further converted into three directions of the vector velocity, can determine the flow velocity and direction of the power flow that is vector synthesized by further calculation.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram showing a configuration of a power flow measuring device according to Embodiment 1 of the present invention. FIG. 2 is an explanatory diagram showing a relationship between a launch angle of a transducer of the power flow measuring device and a distance to a water surface. 3 is a timing chart of signals of respective parts of the tidal current measuring device. In the figure, the same components as those of the conventional example are denoted by the same reference numerals, and the description of the duplicate components will be omitted. Reference numeral 27 denotes a water surface receiver that receives a reflection signal from the transducer element of the transducer 8 that is the same as the receiver 14. Here, the amplification degree differs between the receiver 14 and the receiver for water surface 27, and the receiver 14 is set to be higher than the receiver 27. The reason is that a certain level is required to detect the reflected signal from the transducer element of the transducer 8, but the receiver 14 is for receiving the reflected signal from fine particles such as plankton in the sea. Since the reflection by the fine particles has a very low reflectance, the amplification degree is set relatively high in the receiver 14, and the water surface receiver 27 is for receiving the reflection signal from the boundary surface of the water surface. Since the reflection from the boundary surface of the water surface has a high reflectance, the amplification factor of the water surface receiver 27 is set relatively low.

Reference numeral 28 denotes a level detector for detecting a reflection signal reflected on the water surface 10 of the water surface receiver 27, 29 denotes a flip-flop, a set terminal S is connected to the arithmetic and control unit 1, and a reset terminal R is a level It is connected to the output side of the detector 28. 30 is a known predetermined frequency, for example, 750
, An AND gate having one input connected to the output terminal Q of the flip-flop 29 and the other input connected to the output of the oscillator 30.
Is connected to the output side of the AND gate 31, and the operational amplifier 1
From the time when the transmission command to the oscillator 2 is transmitted
The counter measures the time until the ultrasonic wave reflected at 0 is received by the transducer 8 and outputs the measured value to the arithmetic and control unit 1.

Next, the operation of the power flow measuring device according to the first embodiment of the present invention will be described. First, after the burst signal oscillated by the oscillator 2 based on the transmission command shown in FIG. 3A from the arithmetic and control unit 1 is amplified to a certain level by the power amplifiers 3, 4, 5, and 6 (FIG. The output of the power amplifier 3 is shown), and the signal is applied to the transducer 8 installed on the sea floor via the transmission / reception switch 7, 11, 12, 13 to convert an electric signal into an ultrasonic wave. The ultrasonic wave emitted obliquely upward from 8 and transmitted to the medium 9 to be measured in seawater in four directions is reflected by the fine particles contained in the medium 9 to be measured and received by the transducer 8. Is converted into an electric signal, and the electric signal is transmitted / received by switches 7, 11, 12, 13
, And is amplified to a certain level by the receivers 14, 18, 21, and 24, and the Doppler shift detection circuits 15, 19, 2
2 and 25 (c in FIG. 3 shows the output of the receiver 14), and the Doppler shift detection circuits 15, 19, 22, 25
Measure the Doppler frequency shift between the frequency of the signal of the oscillator 2 and the frequency of the received signal. The operation so far is the same as that of the conventional example.

Next, the Doppler shift detection circuits 15, 1
The Doppler frequency shifts measured by 9, 22, and 25 are selectively extracted at the timing of the sampling timing signal from the arithmetic and control unit 1, and the extracted Doppler shift frequencies are A / D converters 16, 20, 23, and 26. An analog signal is converted into a digital signal by the above-described operation, and the converted signal is input to the operation controller 1. However, in the first embodiment, a predetermined operation control unit 1
Rather than selecting and extracting Doppler frequency shifts measured by the Doppler shift detection circuits 15, 19, 22, and 25 at the timing of the sample timing signal from the receiver, when the tide level of the sea to be measured changes, transmission and reception are performed. The signals of the frequency shift measured by the Doppler shift detection circuits 15, 19, 22, and 25 are selected and extracted at the timing of the sampling timing signal corresponding to the distance D from the detector 8 to the changed water surface 10 immediately above, and the change is detected. The flow velocity v of each tidal current on the surface at the calculated tide level is calculated, and further converted into vector velocities in four directions, and then the flow velocity and direction of the tidal current combined by the calculation are obtained.

Hereinafter, the operation of the first embodiment of the present invention will be described in detail. The water surface receiver 27 receives a reflection signal from the boundary surface of the water surface 10 and outputs the signal to the level detector 28. The level detector 28 inputs the reflected signal from the receiver 27 to the reset terminal R of the flip-flop 29. The flip-flop 29 is set by the transmission command shown in FIG. This is a signal when the ultrasonic wave is emitted from the transducer 8. Then, the flip-flop 29 is reset by a reflection signal of the water surface 10 from the level detector 28.

Accordingly, the period from when the flip-flop 29 is set as shown in FIG. 3f to when it is reset, that is, after the transmission command output from the arithmetic and control unit 1 is issued, to FIG. As shown, the level detector 28 is
Until the reflected signal of 0 is received and output, the AND gate 31 is opened and the oscillator 30 outputs, for example, 750 Hz.
Is measured by the counter 33, and the measured value is output to the arithmetic and control unit 1. If the counter 33 measures, for example, one second, the C (sound speed) is 1500 m / s, so the distance L of the propagation path from the transducer 8 to the water surface 10 is L.
Is 1500/2 = 750 (m) because the ultrasonic wave reciprocates
Since the launch angle θ of the ultrasonic wave of the transducer 8 is predetermined, the distance D from the transducer 8 to the water surface 10 immediately above can be obtained by calculating D = cos θ · L, The arithmetic control unit 1 calculates the distance D calculated on the display 17.
Is displayed. Thus, even if the tide level of the sea fluctuates, the distance D from the transducer 8 to the water surface 10 immediately above can be obtained.

Therefore, for example, when the tide level of the sea to be measured changes, even if it is initially set so that the surface tidal current can be measured at the lowest tide level of the sea, the transmitter / receiver 8, which is the highest tide level of the sea, If the distance D to the water surface 10 immediately above is known, each Doppler shift detection circuit 15, 19, 22, 25 can be measured so that the tidal current near the water surface can be measured at the maximum tide level of the sea.
By extracting the Doppler frequency shift measured by the sampling timing signal (t = 2D / C · cos θ) shown in FIG. 3C corresponding to the distance D from the transducer 8 to the water surface 10 immediately above, Based on the Doppler frequency shift measured by each Doppler shift detection circuit 15, 19, 22, 25, the arithmetic and control unit 1 determines the flow velocity v of each tidal current near the water surface at the maximum tide level of the sea which greatly affects the operation of the ship. Can be calculated accurately, and after converting to vector flow velocity in 4 directions,
Further, the flow velocity and the direction of the tidal current vector-combined by calculation are obtained, and these can be displayed on the display 17.

Embodiment 2 In the first embodiment, when measuring the flow velocity of the tidal current near the water surface, when the tide level of the water surface 10 changes, the distance from the transducer to the water surface is measured, and the sampling timing corresponding to the distance is measured. By extracting the Doppler frequency shift measured by each Doppler shift detecting circuit at the timing of the signal, the flow velocity of the changed tidal current near the water surface is obtained. In the second embodiment, not only the flow velocity of the tidal current near the water surface, which is the upper layer, but also the flow velocity of the lower tidal current, which is lower than the middle layer, is obtained. Is the same as that of the first embodiment, and the description of the configuration is omitted.

In the second embodiment, initially, the distance from the transducer 8 to the upper water surface 10, the distance to the middle layer,
Since the distance to the lower layer is known in advance, each of the Doppler shift detection circuits 15, 19, 22, 25 is set at the timing of the sampling timing signal corresponding to each distance.
By extracting the measured Doppler frequency shift, the flow velocity of the tidal current in the upper layer, the middle layer, and the lower layer can be obtained. Here, when the tide level of the water surface 10 that is higher than the initially planned tide level changes and becomes the minimum tide level,
The lowest upper tide can reach the middle tide. If the tide level on the water surface 10 falls as described above and the flow velocity near the water surface 10 becomes unstable, it may not be said that an accurate flow velocity is measured even if the minimum tide level flow velocity is obtained.

Therefore, when the tide level of the water surface 10 drops and the flow velocity is unstable, the Doppler shift detection circuits 15, 19, and, at the timing of the sampling timing signal corresponding to the distance from the transducer 8 to the water surface 10 in the upper layer. 22 and 25 take out the measured Doppler frequency shift, measure the minimum tidal flow velocity in the upper layer, and also measure the timing of the sampling timing signal corresponding to the distance shorter than the initial level for the middle and lower layers by the change in tide level. The Doppler frequency shifts measured by the respective Doppler shift detection circuits 15, 19, 22, 25 are taken out, and the tide levels of the middle and lower layers are measured. By measuring the tidal velocities of the upper, middle and lower layers in this way, even if the tide level of the water surface decreases and the flow velocity is unstable, the accurate flow velocity of the upper tier can be predicted from the stable flow velocity of the middle tier.

In the first and second embodiments, the method in which the transducer 8 transmits and receives four ultrasonic beams at the same time is employed. Even if one receiver is used, the same effect is generated because the tide level and the tide flow change very slowly. Further, in the first and second embodiments, the method using four ultrasonic beams has been described. However, it is possible to measure the flow velocity of each vector with three or more ultrasonic beams and combine them to obtain the azimuth. Needless to say.

[0024]

As described above, the present invention is installed on the sea floor, emits at least three ultrasonic waves obliquely upward in three directions, and receives three ultrasonic waves reflected by a measurement medium in the sea. Output by the transducer that converts it to an electrical signal
Amplification is weaker than the three receivers that amplify each of the three electric signals. A receiver for the water surface that amplifies the electric signal based on the ultrasonic wave reflected on the water surface, a transmission command to the oscillator of the arithmetic control unit, and reception for the water surface. A counter that measures the time between when the device receives the electric signal at a predetermined frequency,
The arithmetic control unit calculates the distance from the transducer to the water surface directly above the transducer based on the time measured by the counter, and outputs a sampling timing signal corresponding to the distance to the frequency of the oscillator signal and the electric power output from each receiver. Since the signals are output to the three Doppler shift detection circuits for measuring the Doppler frequency shift with respect to the frequency of the signal, even when the tide level of the sea to be measured changes, the operational amplifier can output the sample from each Doppler shift detection circuit.・ Based on the Doppler frequency shift extracted at the timing of the timing signal, it is possible to accurately calculate the flow velocity of each tidal current near the water surface at the changed tide level of the sea, which greatly affects the operation of the ship, and further, vectors in three directions After the conversion into the flow velocity, there is an effect that the flow velocity and direction of the tidal current vector-combined by calculation can be further obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a power flow measuring device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a launch angle of a transducer of the tidal current measuring device and a distance to a water surface.

FIG. 3 is a timing chart of signals of each part of the tidal current measuring device.

FIG. 4 is a block diagram showing a configuration of a conventional power flow measuring device.

FIG. 5 is a timing chart of signals of respective parts of the tidal current measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Operation control part 2 Oscillator 8 Transducer 9 Measurement medium (seawater) 10 Water surface 14 Receiver 15 Doppler shift detection circuit 18 Receiver 19 Doppler shift detection circuit 21 Receiver 22 Doppler shift detection circuit 24 Receiver 25 Doppler Deviation detection circuit 27 Water level receiver 32 Counter

Claims (2)

[Claims] An oscillator that oscillates an electric signal of a predetermined frequency based on a transmission command, and is installed on the sea floor and emits at least three ultrasonic waves obliquely upward in three directions based on the electric signal of the oscillator. , Reflected by the underwater measurement medium 3
A transducer that receives two ultrasonic waves and converts them into electrical signals;
Three receivers for amplifying three electric signals output from the transducer, and three Doppler shifts for measuring the Doppler frequency shift between the frequency of the oscillator signal and the frequency of the electric signal output from each receiver. A transmission command is output to the detection circuit and the oscillator, and a predetermined sampling timing signal is output to each Doppler shift detection circuit to calculate a flow velocity of each tidal current based on the Doppler frequency shift extracted at a predetermined timing. A flow control device for calculating the flow velocity and direction of the tidal flow that has been vector-combined by calculation after converting into a vector flow in three directions, wherein one of the three electrical signals output by the transducer is A water level receiver that amplifies an electric signal based on ultrasonic waves reflected at the water surface, the amplification degree being lower than the three receivers, and the arithmetic control unit A counter for measuring a time between a transmission command time to the oscillator and a time when the water surface receiver receives the electric signal at a predetermined frequency, the arithmetic control unit based on the time measured by the counter. Calculate the distance from the transducer to the water surface directly above it,
A tidal current measuring device wherein a sampling timing signal corresponding to the distance is output to the three Doppler shift detection circuits. 2. The arithmetic control unit includes: a sampling timing signal for extracting a Doppler frequency shift of an ultrasonic wave reflected near a water surface, which is an upper layer, from each of the Doppler shift detection circuits; A sampling timing signal for extracting the Doppler frequency shift of the sound wave, and a sampling timing signal for extracting the Doppler frequency shift of the ultrasonic wave reflected from the lower layer below the middle layer are output, and the counter is activated when the tide level of the water surface falls. Based on the measured time, the distance from the transducer to the upper water surface immediately above it is calculated, and a sampling timing signal corresponding to the distance is output to the Doppler shift detection circuit. The Doppler shift detection of the sample timing signal corresponding to the distance shorter than the initial 2. The power flow measuring device according to claim 1, wherein the power flow is output to an output circuit.