JP3766714B2 - Electromagnetic flow meter with flume - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of an electromagnetic flow meter having a flume suitable for measuring sewage and drainage.
[0002]
[Prior art]
The applicant of the present application has a so-called perma bolus flume in a flow pipe as a flow meter of an open channel through which fluid flows in a non-full state, and measures the flow velocity upstream of the throat portion or the throat portion by the principle of electromagnetic induction. An electromagnetic flow meter was proposed (Japanese Patent Laid-Open No. 5-273015).
[0003]
In this prior art, for example, as shown in FIG. 2, a perm / bolus flume 2 is provided in a flow tube 1, and an electrode 3 facing the horizontal direction is disposed on the flume 2. An exciting coil 4 is provided below the flow tube 1 to generate a vertical magnetic field in the figure. A voltage proportional to the flow velocity induced in the electrode 3 is amplified by the amplifier 5, converted into a digital signal by the A / D converter 6, and then the flow rate is calculated by the arithmetic circuit 7. Reference numeral 8 denotes an excitation power source for exciting the excitation coil 4, and 9 denotes a timing circuit for generating timing signals necessary for measurement and excitation.
[0004]
Assuming that the voltage proportional to the flow velocity induced in the electrode 3 is e, the flow rate Q is Q = F (e) as a function F (e) of the voltage e.
It is expressed.
[0005]
The function F is a function determined by the installation position of the flowmeter 1 and the shape of the electromagnetic flowmeter, the shape of the electrode 3, the magnetic flux density distribution of the magnetic field, and these parameters are fixed and measured in advance. I ask for it.
[0006]
By doing so, the flow rate in the non-full state is measured without measuring the water level.
[0007]
[Problems to be solved by the invention]
In the conventional technique, the flow rate at the throat part or upstream of the throat part is measured using the principle of electromagnetic induction, and the flow rate is calculated by using a constant functional relationship between the measured flow rate and the flow rate. is doing.
[0008]
However, the water level is near the boundary line 10 between the upper end of the throat portion of the flume 2 and the inner periphery of the flow tube 1, that is, before and after the water level ho at the boundary position between the upper end of the throat portion and the inner periphery of the flow tube 1 as shown in FIG. Then, since the water level becomes a bivalent function with respect to the flow velocity signal voltage e as shown in FIG. 3C over a certain range Δh of the water level, the accuracy of the flowmeter at this portion is not good. was there.
[0009]
This phenomenon occurs because the channel cross-sectional area changes with the rise of the water level, but is completely different from the position of the above-mentioned ho, and the tendency of the flow velocity distribution in the throat portion differs before and after the water level ho. is there.
[0010]
More specifically, since the side surface of the throat constituting the flume is flat and the boundary with the inner peripheral surface of the flow tube 1 is clear, the influence of the flow velocity distribution change is concentrated on the water level near this boundary. Since it appeared, the relationship between the flow velocity value and the water level was bivalent.
[0011]
Accordingly, an object of the present invention is to propose an electromagnetic flow meter having a flume that can eliminate such problems.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 is a flow meter for an open channel through which a fluid flows in a non-full state, and has a flume (2) in a flow pipe (1), and the flume portion Or in an electromagnetic flowmeter that measures the upstream flow velocity according to the principle of electromagnetic induction,
The throat side surface portion is formed so that the side surface upper end portion (2b) of the throat portion (2a) of the flume (2) and the inner peripheral surface (1a) of the flow tube (1) are smoothly connected. An electromagnetic flow meter having a flume.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
1 (a) and 1 (b) show a preferred embodiment of the present invention, and the side surface upper end 2b of a throat portion 2a of a perm bolus-like flume 2 provided in a flow tube 1 is shown in FIG. 1 (a). The side surface upper end portion 2a of the throat portion 2a is formed so as to be formed in an arc shape so that the side surface upper end portion 2b and the inner peripheral surface 1a of the flow tube 1 are smoothly connected.
[0014]
By doing so, the water level becomes a monovalent function over a relatively wide range Δh in the vicinity of the water level ho with respect to the flow velocity signal voltage e as shown in FIG.
In this invention, the throat side surface portion and the inner peripheral surface of the flow tube are connected by a smooth curved surface, and a clear boundary line is not created. The bivalent relationship between the flow velocity and the water level is eliminated, and the accuracy of the flow meter is improved.
[0015]
【The invention's effect】
Since the electromagnetic flowmeter of the present invention is configured as described above, the relationship between the induced voltage proportional to the flow velocity and the water level, in other words, the relationship between the flow velocity and the flow rate is always a monovalent function, and thus the flow rate measurement. Accuracy is improved.
[Brief description of the drawings]
1A is a schematic cross-sectional view of a preferred embodiment of the present invention, FIG. 1B is a schematic vertical cross-sectional view of FIG. 1A, and FIG. 1C is an embodiment of FIGS. It is a diagram explaining the relationship between the flow velocity signal voltage and the water level.
FIG. 2 is a block diagram of the prior art.
3A is a schematic cross-sectional view of a conventional detector portion, FIG. 3B is a schematic vertical cross-sectional view of FIG. 3A, and FIG. 3C is a flow rate signal voltage of FIGS. It is a diagram explaining the relationship with a water level.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flow pipe 1a Inner peripheral surface 2 Flume 2a Throat part 2b Side surface upper end part of throat part 2a

Claims (1)

A flow meter for an open channel in which fluid flows in a non-full state, having a flume (2) in the flow pipe (1), and measuring the flow velocity at the flume portion or upstream thereof based on the principle of electromagnetic induction In total
The throat side surface portion is formed so that the side surface upper end portion (2b) of the throat portion (2a) of the flume (2) and the inner peripheral surface (1a) of the flow tube (1) are smoothly connected. Electromagnetic flow meter with flume.

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