JPH0687019B2 - Flowmeter and flow measurement method - Google Patents

Description

The present invention relates to a flow meter and a flow rate measuring method.

[Conventional technology]

As a flow meter for measuring the flow rate of the fluid flowing in the pipe, in the fluid flow pipe, a float that moves in the pipe axis direction along with the change in the flow rate of the fluid flowing in the pipe is provided, and the moving position of the float is detected, There is one that measures the flow rate of the fluid flowing in the fluid flow pipe from the moving position of the float. Known flowmeters of this type include those that detect the moving position of the float using a differential transformer, and those that detect the moving position of the float using a fluid flow pipe as a transparent pipe by a photoelectric detection method. ing.

However, the flow meter using the differential transformer described above mechanically transmits the position change of the float to the outside of the pipe to operate the differential transformer, and therefore the structure is complicated and it is difficult to miniaturize it. Also, there is a problem that reliability is low because the operation of the mechanical transmission mechanism at a minute flow rate is unstable.
On the other hand, the flowmeter using the photoelectric detection method has a simple structure and can be downsized compared to the differential transformer method, and it is possible to measure minute flow rates with high accuracy, but with this photoelectric detection method,
It is impossible to measure the flow rate of opaque fluid such as polluted fluid,
Therefore, there is a problem that there are restrictions on usage conditions.

For this reason, conventionally, a magnetic field flowmeter (see Japanese Laid-Open Patent Publication No. 62-95425) has been proposed which detects the moving position of the float by using magnetic force.

This magnetic force line flowmeter is provided with a float containing a ferromagnetic material in a fluid flow pipe made of a non-magnetic material, and a detection coil for detecting the float is provided on the outside of the fluid flow pipe in close proximity to the pair. A required number of coil pairs, which are paired with the exciting coil provided along the tube axis direction, are provided at a constant pitch, and an outer cylinder made of a ferromagnetic material is provided outside the coil pair group. There is.

This magnetic field flowmeter applies a rectangular wave exciting current to the exciting coil of each coil pair, detects the moving position of the float from the magnitude of the spike-wave-like electromotive force induced in the detection coil of each coil pair, and detects the flow rate. Is measured and its principle is as follows. If there is no float in the tube, the distribution of the magnetic flux generated by the exciting coil of each coil pair will be biased toward the outer cylinder side made of a ferromagnetic material, and in this state, the induction induced in the detection coil of each coil pair will occur. The power is small.
However, since there is a float containing a ferromagnetic material in the tube, the magnetic flux generated by the exciting coil is affected by the ferromagnetic material in the float in the coil pair at the position where the float is moving among the above coil pairs. The distribution also spreads to the detection coil side (float side). Therefore, the electromotive force induced in the detection coil of each coil pair is large in the coil pair in which the float is close, and small in the other coil pair apart from the float, so if the detection coils of each coil pair are sequentially scanned, The flow rate can be known from the position of the coil pair (the position of the float) where the electromotive force of the detection coil exceeds a predetermined threshold value.

[Problems to be Solved by the Invention]

However, since the above-mentioned conventional magnetic force line flowmeter utilizes the change in the magnetic flux distribution of each coil pair due to the movement of the float, each coil pair provided outside the pipe is provided with the detection coil and the exciting coil as the pipe axis. It is necessary to have a configuration in which they are arranged so as to face each other in a direction orthogonal to each other.
In order to change the magnetic flux distribution due to the movement of the float, it is necessary to provide an outer cylinder made of a ferromagnetic material outside the coil pair group. For this reason, the structure of the magnetic field flowmeter is quite complicated. Moreover, in the above magnetic field flowmeter,
Since the position of the float is detected by sequentially scanning the detection coils of each coil pair, it is difficult to detect the float position. Further, when the float comes to the middle of two adjacent coil pairs, the electromotive force of the detection coils of these two coil pairs exceeds the threshold value, so that the detection accuracy of the float position is not sufficient and therefore the flow rate There was also a difficulty in measuring accuracy.

An object of the present invention is to provide a flow meter which has a simple structure, is easy to detect a float position, and is capable of performing highly accurate flow rate measurement, and a flow rate measuring method using this flow meter. It is in.

[Means for Solving the Problems]

The flowmeter of the present invention includes a fluid flow pipe made of a non-magnetic material, and at least a part of the fluid flow pipe that is provided in the fluid flow pipe and moves in the pipe axis direction in accordance with a change in the flow rate of the fluid flowing through the fluid flow pipe. A float made of a conductor or an unsaturated ferromagnetic material, a float search coil wound around the fluid flow pipe over a range slightly longer than the moving stroke of the float in the flow rate measuring range, and a search coil of this search coil. A pair of exciting coils that are close to both ends and are wound around the fluid flow pipe to generate magnetic fluxes in mutually opposite directions, and the float has a float linkage portion of magnetic flux generated by one exciting coil. The secondary magnetic flux is induced according to the difference between the magnetic flux density of the magnetic field and the magnetic flux density of the magnetic flux generated by the other exciting coil at the interlinkage part of the float. It is characterized in that inducing the electromotive force corresponding to the position of the float Le.

Further, the flow rate measuring method of the present invention applies an exciting voltage of an alternating waveform that generates magnetic fluxes in mutually opposite directions to the pair of exciting coils of the flow meter, and also generates an electromotive force induced in the search coil of the flow meter. The moving position of the float of the flow meter is detected based on the phase difference between the waveform of the electromotive force and the waveform of the exciting voltage.

[Action]

That is, the flowmeter of the present invention is to induce a secondary magnetic flux in the float by the magnetic fluxes of the pair of exciting coils in mutually opposite directions, and to induce an electromotive force in the search coil by the secondary magnetic flux of the float, The secondary magnetic flux induced in the float is a magnetic flux that depends on the difference between the magnetic flux density at the float interlinking portion of the magnetic flux generated by one exciting coil and the magnetic flux density at the float interlinking portion of the magnetic flux generated by the other exciting coil. Yes, the magnetic flux degree of the flux linkage part of the magnetic flux generated by each exciting coil is the distance of the float to each exciting coil,
That is, it changes depending on the position of the float. Therefore,
The secondary magnetic flux induced in the float changes according to the position change of the float with the flow rate change, and the electromotive force induced in the search coil by the secondary magnetic flux of the float also changes according to the position change of the float. The moving position of the float, that is, the flow rate of the fluid can be known from this electromotive force.

This flow meter has a search coil and a pair of excitation coils near both ends of the search coil wound around a fluid flow pipe made of a non-magnetic material, and at least a part of the fluid flow pipe is made of non-magnetic conductive material. The structure is simple because it is only provided with a float made of a body or an unsaturated ferromagnetic material, and therefore, the cost and the size can be reduced. Further, since this flow meter changes the induced electromotive force of one search coil provided over a range slightly longer than the movement stroke of the float within the flow rate measurement range by the movement of the float, the conventional magnetic flux line flow rate described above is used. It is not necessary to sequentially scan the detection coils of each coil pair like a meter, and therefore the float position can be easily detected, and the induced electromotive force of the search coil changes according to the movement of the float. Therefore, it is possible to accurately detect the moving position of the float and perform accurate flow rate measurement.

Further, the flow rate measuring method of the present invention is to detect the moving position of the float from the phase difference between the waveform of the electromotive force induced in the search coil and the waveform of the excitation voltage of the alternating waveform applied to the pair of excitation coils. The phase of the electromotive force output from the search coil changes even with a slight movement of the float. Therefore, according to this flow rate measuring method, the moving position of the float is accurately detected to measure the flow rate with high accuracy. Can be done.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view of the flowmeter of this embodiment. Note that this flow meter is a vertical type that is interposed at the rising portion of the pipe.

In FIG. 1, reference numeral 1 denotes a fluid flow pipe interposed at a rising portion of a pipe (not shown), and the fluid flow pipe 1 is supported between a pair of upper and lower end pipes 2 and 3. 4 is the above end tube
It is a connecting rod that connects 2 and 3. The end pipes 2 and 3 are provided with pipe connection flanges 2a and 3a, respectively, and the fluid flow pipe 1 separates the rising portions of the pipes and separates the end pipes 2 and 3 into upper and lower pipes thereof. All of them are connected and interposed in the pipe. L indicates the flow direction of the fluid flowing from the pipe into the fluid flow pipe 1.

The fluid flow pipe 1 is made of glass, a hard synthetic resin such as acrylic resin, or a non-magnetic material such as a non-magnetic metal. The fluid flow pipe 1 extends from the inflow side (lower end side) of the fluid to the outflow side ( It is a tapered tube whose diameter increases toward the upper end). A float 5 is provided inside the fluid flow pipe 1.
Is provided.

As shown in FIG. 2, the float 5 has a circular plate 5b having a diameter slightly larger than the circular cylinder 5a at both ends of a circular cylinder 5a having a length of about 10 mm, and a diameter of the bottom surface of the circular cylinder 5a. The tip end member 5c having an inverted conical shape equal to is fixed by means such as adhesion, and the diameter of the disc 5b, which is the maximum diameter portion of the float 5, is the minimum diameter portion (lower end side) of the fluid flow pipe 1. The diameter is slightly smaller than the inner diameter of. The three members 5a, 5 that make up this float 5
Of b and 5c, the central cylindrical body 5a is made of a non-magnetic conductor or an unsaturated ferromagnetic body, and the disc 5b and the tip member 5c are made of synthetic resin.

However, when the fluid flowing in the fluid flow pipe 1 contains impurities such as iron powder that are easily magnetized, the cylindrical body 5a is used.
Is a non-magnetic conductor. This is because if the columnar body 5a has magnetism, impurities in the fluid are magnetized and adsorbed on the columnar body 5a, which changes the weight and outer shape of the float 5. In this case, the cylindrical body 5a is made of a non-magnetic metal having good conductivity, for example, aluminum, brass, 18-8 stainless steel (stainless steel showing an austenitic structure at room temperature) specified by JIS standard, or the like. It is desirable to do.

Further, when the fluid does not contain impurities that are easily magnetized, the cylindrical body 5a may be a ferromagnetic body. Examples of the ferromagnetic substance include samarium, ferrite, alnico, neodymium, and the like, and synthetic resin magnets in which powders of these ferromagnetic substances are contained in a synthetic resin.

The float 5 is provided in the fluid flow pipe 1 with its tip member 5c facing downward (fluid inflow side), and the fluid flowing from the lower end side into the fluid flow pipe 1 is , Through the annular gap between the outer peripheral surface of the float 5 and the inner peripheral surface of the fluid flow pipe 1 to the upper end side of the fluid flow pipe 1. The float 5 tends to settle down in the fluid in the fluid flow pipe 1 due to its own weight. Therefore, the float 5 moves in the pipe axial direction (vertical direction) of the fluid flow pipe 1 with a change in the flow rate of the fluid flowing in the fluid flow pipe 1.
The float 5 floats at a position where the own weight of the float 5 and the float moving force of the fluid are balanced. The float moving force of the fluid is the same as the fluid pressure in front of (below) the float 5,
It is caused by the difference between the pressure of the fluid immediately after the float 5 and the high-speed flow that flows through the annular gap between the float 5 and the fluid flow pipe 1 and flows out behind the float 5. The pressure difference between the fluid before and after the float increases as the flow rate of the fluid increases, but since the fluid flow pipe 1 is a tapered pipe, the pressure difference between the float 5 and the fluid flow pipe 1 is increased. The annular gap becomes larger as the float 5 moves rearward (upward) as the flow rate increases. Therefore, the rate of increase of the pressure difference due to the increase of the flow rate is suppressed by the increase of the flow rate passing through the gap between the float 5 and the fluid flow pipe 1, so that the movement amount of the float 4 with respect to the change of the flow rate is suppressed to be small. be able to. Further, the taper angle of the fluid flow pipe 1 is selected so that the change in the position of the float 5 with respect to the change in the flow rate is as close to a linear relationship (proportional relationship) as possible.

The float 5 is provided at the center of the fluid flow pipe 1.
A guide rod 8 for guiding the is inserted. Both ends of the guide rod 8 are supported by the end tubes 2 and 3 through rod supporting members 9 having fluid passage openings. The float 5 has a through hole 6 provided at the center thereof loosely fitted in a guide rod 8 and slidably supported by the guide rod 8. The guide rod 8 prevents lateral shake. In addition, 8a and 8b are float stoppers provided at both ends of the guide rod 8. Also, on the disk 5b of the float 5, on both sides of the outer periphery,
A notch 7 whose upper surface is inclined in one direction is formed. The notch 7 receives the pressure of the fluid flowing in the fluid flow pipe 1 and applies a rotational force to the float 5. If the rotational force is applied to the float 5 in this way, the weight and the float movement force due to the fluid are exerted. It is possible to reduce vertical vibration of the float 5 floating at a position where and are balanced.

On the other hand, a straight tubular outer tube 10 is provided around the fluid flow tube 1. This outer tube 10 is also made of glass, a hard synthetic resin such as acrylic resin, or a non-magnetic material such as a non-magnetic metal. The outer tube 10 has its center aligned with the center of the fluid flow pipe 1, It is supported between the end tubes 2 and 3.

A float search coil 11 is wound around the outer circumference of the outer tube 10. This search coil 11 is wound at a uniform pitch over a range slightly longer than the moving stroke S of the float 5 within the flow rate measurement range, and both ends of this search coil 11 are output as shown in FIG. 3 [a]. It is connected to terminals 11a and 11b. A pair of exciting coils 12A and 12B are wound around the outer circumference of the outer tube 10 so as to be close to both ends of the search coil 11. These exciting coils 12A and 12B generate magnetic fluxes in mutually opposite directions. Both exciting coils 12A and 12B
The end of the search coil 11 side of is connected by a lead wire 13 as shown in FIG. 3 [a], and both excitation coils 12A, 12B
The end portion on the opposite side of is connected to the excitation voltage input terminals 12a and 12b. For example, when the outer diameter of the outer tube 10 is 24 mm and the movement stroke S of the float 5 within the flow rate measurement range is 80 mm, the number of turns of the search coil 11 is set to 300, the coil length is set to 90 mm, and the exciting coil 12A is set. The number of turns of 12B is 150, and the coil length is 10
Set to mm. Also, the search coil 11 and the excitation coils 12A and 12B
The distance between and is 1 mm.

Next, measurement of the flow rate by the flow meter configured as described above will be described with reference to FIG.

This flowmeter outputs an electromotive force induced in the search coil 11 via the float 5 by the magnetic flux generated by the pair of exciting coils 12A and 12B. When an exciting voltage having an alternating waveform is applied to the exciting coils 12A and 12B. , Magnetic fluxes Fa and Fb having opposite strengths and almost the same strength (magnetic flux density) are generated in the exciting coils 12A and 12B, and the magnetic fluxes Fa and Fb cause electric conductors or magnetic portions of the float 5 (cylindrical body 5a). A secondary magnetic flux is induced in the search coil 11, and an electromotive force having a waveform similar to the excitation voltage is induced in the search coil 11. The alternating waveform excitation voltage applied to the excitation coils 12A and 12B may be a sine wave voltage or a rectangular wave voltage, but a sine wave voltage is used here. The voltage value of this exciting voltage and its frequency are set to values that can sufficiently link the magnetic fluxes Fa and Fb from the exciting coils 12A and 12B to the float 5 regardless of the position of the float 5 within its movement stroke. I am doing it.

The induction of electromotive force in the search coil 11 is based on the following principle.

That is, when the cylindrical body 5a of the float 5 is made of a non-magnetic conductor, the magnetic fluxes Fa, Fb generated by the exciting coils 12A, 12B are
When the conductive part (column 5a) of the
Magnetic flux Fa generated by one exciting coil 12A in the conductive part of
Flux density at the float interlinkage part and the other exciting coil 12B
A voltage is induced according to the difference between the magnetic flux density of the magnetic flux Fb generated by the magnetic flux density and the magnetic flux density of the float interlinking portion, and the induced voltage causes a particle flow to flow in the conductive portion. This current is an alternating current according to the frequency of the exciting voltage applied to the exciting coils 12A and 12B, so this current concentrates in the surface layer of the conductive part due to the skin effect, and this current induces the secondary magnetic flux. To do. Then, the secondary magnetic flux induced in the conductive portion of the float 5 interlinks with the search coil 11 and induces the search coil 11 to generate an electromotive force having a waveform similar to the excitation voltage applied to the excitation coils 12A and 12B.

When the cylinder 5a of the float 5 is made of a ferromagnetic material,
When the magnetic fluxes Fa, Fb generated by the exciting coils 12A, 12B interlink with the magnetic portion (cylindrical body 5a) of the float 5, if the magnetic portion of the float 5 is in an unsaturated state, this magnetic portion will be one of the exciting coils. The magnetic flux density of the magnetic flux Fa generated by 12A and the magnetic flux density of the magnetic flux Fb generated by the other exciting coil 12B is further magnetized by the magnetic force corresponding to the difference between the magnetic flux density of the magnetic flux Fa and the magnetic flux density of the magnetic flux Fa generated by the other exciting coil 12B. Secondary magnetic flux is induced. Also,
When this magnetic part is also conductive, the voltage due to the interlinkage magnetic flux Fa, Fb is also induced in this magnetic part, and the magnetic flux induced by the current flowing through the surface layer of the magnetic part is also superposed on the secondary magnetic flux due to the skin effect. . When the magnetic portion is made of a material having no conductivity such as a synthetic resin magnet, the magnetic flux is not induced by the current. Then, the secondary magnetic flux induced in the magnetic portion of the float 5 interlinks with the search coil 11, and causes the search coil 11 to induce an electromotive force having a waveform similar to the excitation voltage applied to the excitation coils 12A and 12B. However, in this case, when the magnetic portion of the float 5 is in the saturated magnetization state, the float 5 is not magnetized any more, so that the magnetic flux density of this magnetic portion becomes constant regardless of the position of the float 5. Therefore, it is necessary to set the voltage value of the excitation voltage applied to the excitation coils 12A and 12B in a range that does not saturate the magnetic portion of the float 5. The arrival distance of the magnetic fluxes Fa, Fb from the exciting coils 12A, 12B is determined by the voltage value of the exciting voltage applied to the exciting coils 12A, 12B and its frequency, and one or both of this voltage value and the frequency can be increased. For example, even if the voltage value of the excitation voltage applied to the excitation coils 12A, 12B is set within the above range, the magnetic fluxes Fa, Fb will reach a longer distance. Magnetic flux F from coils 12A and 12B
Float 5 can be sufficiently cross-linked with a and Fb.

Focusing on the voltage of the electromotive force output from the search coil 11 (hereinafter referred to as the output voltage), FIG. 3 [b] shows a change in the output voltage e with respect to the moving position of the float 5. As for this output voltage e, the float 5 searches coil 11
Is maximum at one end (end on the left side in FIG. 3 [a]), and becomes gradually smaller as the float 5 moves toward the center of the search coil 11. And
When the float 5 comes to the central position of the search coil 11, the output voltage e becomes the minimum. Also, the float 5 is a search coil
When it moves further beyond the center of 11, the above output voltage e
Is gradually increased again, and becomes maximum when the float 5 reaches the other end of the search coil 11 (the end on the right side in FIG. 3 [a]) (output when the float 5 is near one end of the search coil 11). The voltage is almost the same as the voltage). That is, the voltage output from the search coil 11 changes according to the moving position of the float 5, and the float 5 moves with the change in the flow rate of the fluid flowing in the fluid flow pipe 1,
By detecting the moving position of the float 5 from the output voltage from the search coil 11, the flow rate of the fluid flowing in the fluid flow pipe 1 can be known. In this case, the change in the output voltage e is substantially symmetrical with respect to the float 5 located at the center position of the search coil 11, and therefore, the float 5 can detect the search coil 11 only with the output voltage value at the time of detection. Although it is not known which side it is on the center position, the tendency of the change in the output voltage is obtained from the output voltage before and after the detection, and when the output voltage tends to decrease, the float 5 is set to the search coil.
If the float 5 is located on the one end side of the center of the search coil 11 and the output voltage tends to increase, if the float 5 is determined to be on the other end side of the center of the search coil 11, the transfer position of the float 5 can be known.

Focusing on the phase of the output voltage e from the search coil 11, FIG. 3 [c] shows the change in the phase of the output voltage e with respect to the moving position of the float 5. This output voltage e
When the float 5 is at one end of the search coil 11 (the end on the left side in FIG. 3 [a]), the exciting voltage E applied to the exciting coils 12A and 12B is as shown by the solid line curve.
Waveform (hereinafter referred to as the reference wave) has the same phase (phase difference φ = 0 with the reference wave), and as the float 5 moves away from one end of the search coil 11, there is a deviation from the reference wave. It becomes a phase. The phase difference φ of the output voltage e with respect to the upper reference wave is deviated by 90 ° with respect to the reference wave when the float 5 comes to the center of the search coil 11 as shown by the alternate long and short dash line, and the float 5 is The other end (Fig. 3)
When it comes to the right end portion in [a], it is displaced by 180 ° with respect to the reference wave as shown by the two-dot chain line. That is,
The phase of the voltage output from the search coil 11 is float 5
Therefore, if the phase difference φ of the output voltage e with respect to the reference wave is detected, the movement position of the float 5 is detected from this phase difference φ, and the fluid flow pipe 1
The flow rate of the fluid flowing inside can be known.

The waveforms shown in FIG. 3 [b] and FIG. 3 [c] are waveforms when the cylindrical body 5 a of the float 5 is a non-magnetic conductor, and the cylindrical body 5 a of the float 5 is ferromagnetic. The waveform of the output voltage e in the case of the body is shown in FIG.
The waveform is slightly deviated from the waveform in FIG. 6C in the float movement direction.

That is, the flowmeter induces a secondary magnetic flux in the float 5 by the magnetic fluxes Fa and Fb generated by the pair of exciting coils 12A and 12B provided at both ends of the search coil 11 in mutually opposite directions. The secondary magnetic flux induces an electromotive force in the search coil 11 by the secondary magnetic flux. The secondary magnetic flux induced in the float 5 is the magnetic flux density of the float interlinkage portion of the magnetic flux Fa generated by the one exciting coil 12A and the other exciting coil 12B. It is a magnetic flux according to the difference between the magnetic flux density of the magnetic flux Fb that is generated and the magnetic flux density of the float interlinking portion, and the magnetic flux Fa generated by each exciting coil 12A, 12B is
The magnetic flux density at the float linkage part of Fb is
It changes depending on the distance of the float 5 with respect to 12B, that is, the position of the float 5. Therefore, the secondary magnetic flux induced in the float 5 changes according to the position change of the float 5 due to the flow rate change, and the electromotive force induced in the search coil 11 by the secondary magnetic flux of the float 5 also changes in the position change of the float 5. Therefore, the moving position of the float 5, that is, the flow rate of the fluid can be known from this electromotive force.

The flow meter is a fluid flow pipe 1 made of a non-magnetic material.
A search coil 11 and a pair of exciting coils 12A, 12 near both ends of the search coil 11 are provided on the outer circumference of the outer tube 10 provided around the
The structure is simple and therefore low because only the float 5 made of non-magnetic conductor or unsaturated ferromagnetic substance is provided inside the fluid flow pipe 1. It can be priced and miniaturized. Further, since this flow meter changes the induced electromotive force of one search coil 11 provided over a range slightly longer than the moving stroke S of the float 5 within the flow rate measuring range by moving the float 5, Unlike the conventional magnetic field flowmeter described in the section [Technology], it is not necessary to sequentially scan the detection coils of each coil pair, and therefore the float position can be easily detected, and the induced electromotive force of the search coil 11 is the float 5. Therefore, it is possible to accurately detect the moving position of the float 5 from this electromotive force and measure the flow rate with high accuracy.

Although the moving position of the float 5 can be detected by the output voltage value of the search coil 11 or the phase of the output voltage as described above, the moving position of the float 5 is detected from the output voltage value. In this case, as described above, the tendency of the change in the output voltage is obtained from the output voltage before and after the detection, and when the float 5 is located at one end side from the center of the search coil 11 and the output voltage tends to increase, It is necessary to determine which side the float 5 is with respect to the center position of the search coil 11, and it is difficult to detect the movement amount of the minute float 5 with the voltage value. In order to accurately detect the amount of movement, the method utilizing the phase difference is advantageous.

An embodiment of the flow rate measuring method utilizing this phase difference will be described. FIG. 4 shows a flow rate measuring circuit.
Is a float search coil, and 12A and 12B are excitation coils. 2
Reference numeral 0 denotes an oscillator that generates a sine wave voltage source having a predetermined frequency (for example, 2 KHz). The sine wave voltage from the oscillator 20 is amplified by the buffer amplifier 21 and applied to the exciting coils 12A and 12B. On the other hand, the voltage of the electromotive force induced in the search coil 11 by the magnetic flux generated in the exciting coils 12A and 12B (the magnetic flux in the opposite directions), that is, the sine wave voltage output from the search coil 11, is first amplified by the preamplifier 22, Further, after noise is removed by the active filter 23, it is sent to the phase difference detection circuit 24.

As shown in FIG. 5, the phase difference detection circuit 24 includes a first zero-cross detector 241 to which the sine wave voltage E from the oscillator 20 is input, that is, a reference wave, and an output voltage e from the search coil 11, that is, It is composed of a second zero-cross detector 242 to which a detected wave is input and a flip-flop 243. The operation of the phase difference detection circuit 24 will be described. In FIG. 6, [a] is the first zero cross detector 241.
The waveform of the reference wave input to the second zero-cross detector 242 is the waveform of the detection wave input to the second zero-cross detector 242. Here, when the phase of the detection wave deviates from the phase of the reference wave by 90 °, (When float 5 is in the center of search coil 11)
Shows the waveform of. Zero cross detector 241, above
The reference wave or the detected wave input to the 242 is 0.
It detects the moment when the level is crossed, and a rectangular wave signal E'as shown in FIG. 6 [c] is input from the first zero cross detector 241 to the C terminal of the flip-flop 243.
A rectangular wave signal e'as shown in FIG. 6 [d] is input to the R terminal of the flip-flop 243 from the second zero-cross detector 242. Then, the flip-flop 243
Turns on when the rectangular wave signal input from the first zero-cross detector 241 to the C terminal rises, and turns off when the rectangular wave signal input from the second zero-cross detector 242 to the R terminal rises. Therefore, as shown in FIG. 6 [e], the flip-flop 243 outputs a rectangular wave signal having a pulse width corresponding to the phase difference φ between the reference wave and the detected wave as the phase difference signal M.

The phase difference signal M output from the flip-flop 243 of the phase difference detection circuit 24 is the phase difference → voltage conversion circuit 25.
Is converted into a DC voltage according to the phase difference. FIG. 7 shows the output of the phase difference → voltage conversion circuit 25, and this output changes in accordance with the change in the phase difference, that is, the float movement position. The output of this phase difference → voltage conversion circuit 25 is
The linearity correction circuit 26 corrects the voltage signal to change linearly according to the change in the float movement position as shown in FIG. 8, and then is input to the level converter 27. This level converter 27 has a linearity correction circuit 26 shown in FIG.
Is inputted to the VI converter 28 as a signal as shown in FIG. 9 in which the voltage value becomes 0 when the phase difference is 0. The VI converter 28 converts the voltage value of the voltage signal into a current value of 4 mA to 20 mA and outputs this current signal as a flow rate signal.

In this embodiment, the output of the phase difference → voltage conversion circuit 25 is corrected by the directness correction circuit 26 into a voltage signal that changes linearly. However, the fluid flow pipe 1 is positioned at the position of the float 5 with respect to the flow rate change. By designing the taper shape so that the change has a substantially perfect linear relationship, the output of the phase difference detection circuit 24 can be a voltage signal that changes linearly. In that case, the linearity correction circuit 26 described above is used. Is unnecessary.

That is, the flow rate measuring method described above uses the float 5 based on the phase difference between the waveform of the electromotive force output from the search coil 11 of the flow meter and the waveform of the alternating voltage applied to the pair of exciting coils 12A and 12B. Is to detect the moving position of, the phase of the electromotive force output from the search coil 11 is,
Since the flow rate changes even with a slight movement of the float 5, the flow rate measuring method can accurately detect the moving position of the float 5 and perform high-precision flow rate measurement.

In the above embodiment, the vertical flowmeter interposed in the rising portion of the pipe and the flow rate measurement using this flowmeter have been described, but the present invention is applied to the non-rise portion of the pipe (horizontal pipe portion, etc.). It can also be applied to an intervening horizontal flow meter.

FIG. 10 shows another embodiment of the present invention, in which the flow meter of this embodiment is a horizontal type.

In FIG. 10, 31 is a fluid flow pipe, and this fluid flow pipe 31 is supported between a pair of end pipes 32 and 33. Reference numeral 34 is a connecting pipe that connects the end pipes 32 and 33. End tube 3 above
2 and 33 are provided with pipe connection holes 32a and 33a, respectively, and the fluid flow pipe 31 is separated from the above pipes, and the end pipes 32 and 33 are respectively screwed into both pipes to be connected to the above pipes. To be done. L indicates the flow direction of the fluid flowing from the above pipe into the fluid flow pipe 31.

The fluid flow pipe 31 is made of a non-magnetic material, and the fluid flow pipe 31 has a tapered tubular shape whose inner circumference increases from the fluid inflow side to the fluid outflow side, and a straight outer tube. It is said that. Inside the fluid flow pipe 31, a cylindrical float 35 is provided. The float 35 is entirely made of a non-magnetic conductor (aluminum, brass, etc.) or an unsaturated ferromagnetic substance (samarium, ferrite, synthetic resin magnet, etc.).
The outer peripheral surface on the tip side is a tapered surface whose diameter decreases toward the tip. The diameter of the float 35 is slightly smaller than the inner diameter of the smallest diameter portion of the fluid flow pipe 31. The float 35 is provided in the fluid flow pipe 31 with its tip facing the inflow side of the fluid.

The float 35 is provided at the center of the fluid flow pipe 31.
Guy rod 36 that guides is inserted. Both ends of the guide rod 36 are supported by both ends of the fluid circulation pipe 31 via rod supporting members 37 having fluid circulation openings.
The float 35 is slidably supported by the guide rod 36, and the guide rod 36 prevents lateral shake. Further, 38 is a coil spring interposed between the float 35 and the rod support member 37 on the fluid flow side to press the float 35 toward the fluid inflow side, and the float 35 flows into the fluid flow pipe 31. The fluid moves in the pipe axis direction of the fluid flow pipe 31 as the flow rate of the fluid changes, and floats at a position where the float moving force of the fluid and the spring force of the coil spring 38 are balanced.

On the other hand, around the fluid flow pipe 31, a straight tubular outer pipe 40 made of a non-magnetic material is provided.
Is supported between the end pipes 32, 33 with its center aligned with the center of the fluid flow pipe 31.

A float search coil 41 is wound around the outer tube 40. The search coil 41 is wound at a uniform pitch over a range slightly longer than the movement stroke S of the float 35 within the flow rate measurement range, and both ends of the search coil 41 are connected to output terminals. Further, a pair of exciting coils 42A and 42B are wound around the outer circumference of the outer tube 40 so as to be close to both ends of the search coil 41. This exciting coil 42A, 4
2B generates magnetic fluxes in opposite directions.The ends of both exciting coils 42A and 42B on the search coil 41 side are connected by a lead wire, and the opposite ends of both exciting coils 42A and 42B are excited. It is connected to the voltage input terminal.

The flowmeter of this embodiment also induces a secondary magnetic flux in the float 35 by the magnetic fluxes in mutually opposite directions generated by the pair of exciting coils 42A and 42B provided at both ends of the search coil 41, and the secondary magnetic flux of the float 35. Is used to induce an electromotive force in the search coil 41, and the secondary magnetic flux induced in the float 35 is
A magnetic flux corresponding to the difference between the magnetic flux density of the float interlinking portion of the magnetic flux generated by one exciting coil 42A and the magnetic flux density of the float interlinking portion of the magnetic flux generated by the other exciting coil 42B,
The magnetic flux density of the magnetic flux generated by the exciting coils 42A and 42B at the float interlinking portion changes depending on the distance of the float 35 from the exciting coils 42A and 42B, that is, the position of the float 35. Therefore, the secondary magnetic flux induced in the float 35 changes according to the position change of the float 35 due to the flow rate change, and the electromotive force induced in the search coil 41 by the secondary magnetic flux of the float 35 also changes in the position change of the float 35. Therefore, the moving position of the float 35, that is, the flow rate of the fluid can be known from this electromotive force.

Further, this flowmeter also has a fluid flow pipe 31 made of a non-magnetic material.
A search coil 41 and a pair of excitation coils 42A, 42B close to both ends of the search coil 41 are provided on the outer circumference of the outer tube 40 provided around the search coil 41.
And a float 35 made of a non-magnetic conductor or an unsaturated ferromagnetic substance are provided in the fluid flow pipe 31, so that the structure is simple, and therefore the cost is low and the size is small. Can be changed. In addition, this flowmeter has one search coil provided over a range slightly longer than the movement stroke S of the float 35 within the flow rate measurement range.
Since the induced electromotive force of 41 is changed by the movement of the float 35, it is easy to detect the float position, and the induced electromotive force of the search coil 41 changes corresponding to the movement of the float 35. It is possible to accurately detect the moving position of the float 35 from the electromotive force and measure the flow rate with higher accuracy.

Also in the flowmeter of this embodiment, it is advantageous to detect the moving position of the float 35 by utilizing the phase difference, but the method may be according to the above-described embodiment.

The flowmeter of this embodiment can be used as it is as a vertical flowmeter.

Further, in each of the above-mentioned embodiments, the float 5 and 35 are connected to the guide rod.
The guide rod is not necessary in the case of a vertical type flow meter and a flow meter for a small flow rate in which the diameter of the fluid flow pipe is small.

Further, in each of the above embodiments, the straight tubular outer tubes 10 and 40 are provided around the fluid flow tubes 1 and 31, and the search coils 11 and 41 and the excitation coils 12A, 12B and 42A, on the outer circumference of the outer tubes 10 and 40. 42B is wound, but as in the embodiment shown in FIG.
If the outer circumference of 31 is a straight pipe,
Search coil 41 and excitation coils 42A, 42B directly on the outer periphery of 31
May be wound, in which case the outer tube 40 is unnecessary.

Further, as in the embodiment shown in FIG. 10, when the float 35 is pressed against the fluid inflow side by the coil spring 38,
The fluid flow pipe 31 may be a straight pipe whose inner diameter is the same from the fluid inflow side to the fluid outflow side. However, when the fluid flow pipe 31 is a straight pipe as described above, the position change of the float 35 with respect to the change of the flow rate of the fluid is
Although there is no direct relationship as in the case of using a tapered tube, the relationship of the float position change to the flow rate change when the fluid flow pipe 31 is a straight pipe is obtained in advance, and the flow rate measurement circuit is designed accordingly. Whether or not, if the winding pitch of the search coil 41 is changed, the same flow rate measurement as in the above embodiment can be performed.

〔The invention's effect〕

The flowmeter of the present invention has a search coil wound around a fluid flow pipe made of a non-magnetic material and a pair of search coils close to both ends of the search coil, and a part of the search coil is not inferred in the fluid flow pipe. Since only the float made of the magnetic conductor or the unsaturated ferromagnet is provided, the structure is simple, and therefore the cost and the size can be reduced. Further, this flowmeter changes the induced electromotive force of one search coil provided over a range slightly longer than the movement stroke of the float within the flow rate measurement range by moving the float. It is not necessary to sequentially scan the detection coils of each coil pair, and therefore the float position detection is easy, and the induced electromotive force of the search coil changes in response to the movement of the float. It is possible to accurately detect the moving position and perform accurate flow rate measurement.

Further, the flow rate measuring method of the present invention detects the moving position of the float from the phase difference between the waveform of the electromotive force output from the search coil and the waveform of the excitation voltage of the alternating waveform applied to the pair of excitation coils. Since the phase of the electromotive force output from the search coil changes even with a slight movement of the float, according to this flow rate measuring method, the moving position of the float is accurately detected, and the flow rate with high accuracy is obtained. The measurement can be performed.

[Brief description of drawings]

1 to 9 show an embodiment of the present invention. FIG. 1 is a sectional view of a flow meter, FIG. 2 is an exploded perspective view of a float, and FIG. 3 is a search coil by movement of the float. Of the output voltage and its phase, Fig. 4 is a flow rate measurement circuit diagram, Fig. 5 is a phase difference detection circuit diagram, Fig. 6 is an input / output waveform diagram of the phase difference detection circuit, and Fig. 7 is a position diagram. FIG. 8 is a diagram showing the output of the phase difference → voltage conversion circuit, FIG. 8 is a diagram showing the output of the linearity correction circuit, and FIG. 9 is a diagram showing the output of the level converter.
FIG. 10 is a sectional view of a flowmeter showing another embodiment of the present invention. 1,31 …… Fluid flow pipe, 5,35 …… Float, S …… Float moving stroke, 11,41 …… Search coil, 12A, 12B, 42
A, 42B ... Excitation coil.

Claims (2)

[Claims] 1. A fluid flow pipe made of a non-magnetic material, and at least a part of which is moved in the pipe axial direction in accordance with a change in the flow rate of a fluid provided in the fluid flow pipe and flowing in the fluid flow pipe. Alternatively, a float made of an unsaturated ferromagnetic material, a float search coil wound around the fluid flow pipe over a range slightly longer than the moving stroke of the float in the flow rate measurement range, and at both ends of this search coil. And a pair of exciting coils that are close to each other and are wound around the fluid flow pipe to generate magnetic fluxes in mutually opposite directions, and the float has a magnetic flux at a float interlinking portion of the magnetic flux generated by one exciting coil. A secondary magnetic flux is induced according to the difference between the density and the magnetic flux density of the magnetic flux generated by the other exciting coil at the float interlinking portion, and the secondary magnetic flux of this float causes the secondary coil to move to the search coil. Flowmeter, characterized in that inducing the electromotive force corresponding to the position of the funnel. 2. An exciting voltage having an alternating waveform for generating magnetic fluxes in mutually opposite directions is applied to a pair of exciting coils of the flow meter according to claim 1, and an electromotive force induced in a search coil of the flow meter is applied. A flow rate measuring method, which comprises detecting and detecting the moving position of the float of the flow meter from the phase difference between the waveform of the electromotive force and the waveform of the exciting voltage.