JPH09145435A - Electromagnetic flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic flow meter having stable measurement efficiency without causing a measurement error affected by the external magnetic field by providing a magnetic field generating means, electrodes, and a magnetic shield plate. SOLUTION: A coil 4 is excited to generate the magnetic field in the direction perpendicular to the axis of a measuring tube 1, and electromotive force is generated when a measured fluid 2 is moved in the measuring tube 1 located in the magnetic field. If the magnetic field is generated perpendicularly to the electrically insulated measuring tube 1 and the conductivity of the flowing fluid is not too low, the electromotive force can be measured between a pair of electrodes 5. The electromotive force is converted into the signal corresponding to the fluid and outputted by a converter, and the flow can be measured. A magnetic shield plate 10 is provided at the position most apart from the coil 4, the plate 10 hardly attracts the magnetic flux generated by the coil 4, no adverse effect is inflicted on the detection efficiency, and stable measurement can be invariably made without impairing the measurement efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generates a magnetic field in a direction intersecting with a fluid to be measured flowing in a measuring pipe, and an electromotive force generated according to a flow rate of the fluid traversing the magnetic field is measured as a diameter of the measuring pipe. The present invention relates to an electromagnetic flow meter that measures the flow rate by detecting it through at least a pair of electrodes provided facing each other.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing the measuring principle of an electromagnetic flowmeter 50. In the figure, 51 is a measuring tube whose inner surface is lined with Teflon or the like, and 52 is a conductive liquid flowing in the measuring tube 1. Is the fluid to be measured, 53 is the measuring tube 5
1, 54 is a coil wound around the core 53 as a magnetic field generating means, and 55 is at least a pair of electrodes provided at positions facing each other on the diameter of the measuring tube 51 and intersecting the magnetic field. 56 are converters that remove noise and the like from the electromotive force detected by the electrode 55 and convert the electromotive force into a signal corresponding to the flow rate of the fluid 52 to be measured.

FIG. 5 is a partially cutaway front view showing a conventional electromagnetic flow meter. In the figure, 101 is a measuring tube and 10 is a measuring tube.
2 is a fluid to be measured which is a conductive liquid flowing in the measuring tube 101, 103 is a core provided on the outer circumference of the measuring tube 101,
Reference numeral 04 is a coil wound around the core 103 as a magnetic field generating means, reference numeral 105 is at least a pair of electrodes provided at positions facing each other on the diameter of the measuring tube 101 and intersecting the magnetic field,
Reference numeral 107 denotes a magnetic flux feedback outer core which covers the coil 104 and is fixed to the measuring tube 101, and 108 is interposed between the coil 104 and the measuring tube 101 in order to generate a magnetic field in parallel in the diameter range of the measuring tube 101. An inner core 109 is a case that covers the coil 104, the magnetic flux feedback outer core 7, and the inner core 108, and is fixed to the measuring tube 101 by welding.

Next, the operation will be described. When the coil 104 is excited by power supply from a power supply (not shown) through the power supply line 4a, a magnetic field φ is generated through the core 103 in a direction orthogonal to the axis of the measuring tube 101. When the fluid to be measured 102 is moved to the measuring tube 101 in this magnetic field, an electromotive force is generated according to Faraday's law of electromagnetic induction. In this case, the magnetic field φ is generated at right angles to the electrically insulated measuring tube 101, and the electromotive force can be measured between the pair of electrodes 105 unless the conductivity of the fluid under measurement 102 is too low.
This electromotive force is proportional to the strength of the magnetic field φ, the average flow velocity of the fluid 102 to be measured, and the distance between the electrodes.
The flow rate can be measured by taking out through the signal line 106 connected to 05, removing noise, converting the signal into a signal corresponding to the fluid by the converter 56 and outputting the signal as shown in FIG.

That is, when the quantity symbol and unit are as follows, quantity symbol physical quantity unit B magnetic flux density TD inner diameter of measuring tube m v average axial fluid velocity m / s E electromotive force V k constant-Q volume flow rate m According to Faraday's law of ³ / s, the magnitude of the electromotive force E is expressed by the following equation. E = kBDv (1) The volume flow rate is calculated by the following equation in the case of a circular pipe. ^{Q = (πD 2/4)} · v ··· (2) Because of this relationship, equation (1) is expressed by the equation (3). Q = (πD / 4kB) · E (3) Here, assuming that the magnetic flux density B is constant, the flow rate in the measuring tube is obtained by measuring the electromotive force E.

[0006]

Since the conventional electromagnetic flowmeter is constructed as described above, when installed, the iron pipes 110a and 110b made of a ferromagnetic material, as shown by hatching, are shown.
Is connected to the measuring tube 101 by the flange portions 110a-1 and 110b-1, the magnetic flux distribution in the case 109 is drawn by the flange portions 110a-1 and 110b-1 and changes as shown by the chain line, and the signal line The electromotive force extracted via 106 changes. Therefore, the piping 110a, 11
There is a problem in that the measurement value changes depending on whether 0b is attached or not, resulting in a measurement error. In this case, the electromotive force is several mV, and generally, the electromagnetic flowmeter detector is initialized without the flange portion attached. Therefore, the change in the magnetic flux distribution as described above shifts the electromotive force itself, This is amplified by the converter (which amplifies the signal from the detector: not shown), resulting in a considerable deviation from the initial state.

The present invention has been made to solve the above problems, and an object thereof is to obtain an electromagnetic flowmeter having stable measurement efficiency without being affected by a measurement error due to the influence of an external magnetic field.

[0008]

According to a first aspect of the present invention, there is provided an electromagnetic flowmeter which comprises a magnetic field generating means for generating a magnetic field orthogonal to a fluid to be measured in a measuring pipe, and an action of the magnetic field in the fluid to be measured. In order to measure the electromotive force generated in the measurement tube, at least a pair of electrodes are provided so as to face each other on the diameter of the measurement tube, and a magnetic shield plate is provided on the flanges at both ends of the measurement tube.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. 1 is a partially cutaway front view showing an electromagnetic flowmeter according to Embodiment 1 of the present invention, in which 1 is a measuring pipe, 2 is a fluid to be measured which is a conductive liquid flowing in the measuring pipe 1, 3 is a core provided on the outer circumference of the measuring tube 1, 4 is a coil wound around the core 3 as a magnetic field generating means, and 5 is provided on the diameter of the measuring tube 1 so as to face each other and intersect the magnetic field. At least a pair of electrodes, 7 is a magnetic flux feedback outer core which covers the coil 4 and is fixed to the measuring tube 1, and 8 is a coil 4 and the measuring tube 1 for generating parallel magnetic fields in the diameter range of the measuring tube 1. An inner core 9 interposed between the coil 4, the outer core 7 for magnetic flux return, and the inner core 8 is fixed to the measuring pipe 1 by welding. A case 10 is a magnetic shield provided at both ends of the measuring pipe. It is a plate.

The measuring pipe 1 has corrosion resistance on the inner surface and the end surface,
A lining treatment 11 for abrasion resistance is applied, and at the time of this lining treatment, the flange portions 1a at both ends of the measuring pipe 1 are
A ring-shaped magnetic shield plate 10 is arranged on the outer surface of 1b and assembled integrally. Then, on the end surface of the measuring tube after the lining treatment, liquid contact rings 13a and 13b that make the detection part in the case 9 and the measuring fluid the same potential are attached, and the material of the lining treatment 11 is, for example, fluorine resin or chloroprene. Rubber, polyurethane rubber, ceramics, etc. are used. As the material of the liquid contact rings 13a and 13b, for example, stainless steel, platinum / indium, tantalum, titanium, Hastelloy B, Hastelloy C, Monel, conductive fluororesin, or the like is used.

When installed, the electromagnetic flowmeter having the above-mentioned structure is provided with iron pipes 12a, 12b made of a ferromagnetic material, as indicated by hatching.
Are connected to the measuring pipe 1 by the flange portions 12a-1 and 12b-1, and various methods such as a flange connection method, a flange clamping method, a sanitary connection method, and a screw connection method can be used for this connection connection. is there.

Next, the operation will be described. The coil 4 is excited by power feeding from a power source (not shown) through the power feeding line 4a, and a magnetic field is generated in a direction orthogonal to the axis of the measuring tube 1,
When the fluid to be measured 2 is moved to the measuring tube 1 in this magnetic field,
An electromotive force is generated by Faraday's law of electromagnetic induction. In this case, a magnetic field is generated at right angles to the electrically insulated measuring tube, and if the conductivity of the flowing liquid is not too low, the electromotive force can be measured between the pair of electrodes 5. Since this electromotive force is proportional to the strength of the magnetic field, the average flow velocity of the fluid, and the distance between the electrodes, noise is removed from this electromotive force, and this electromotive force is converted into a signal corresponding to the fluid by the converter 56 as shown in FIG. The flow rate can be measured by converting and outputting.

As described above, according to the first embodiment, the outer surfaces of the flange portions 1a and 1b at both ends of the measuring tube, that is, the case 9
Since the magnetic shield plate 10 is provided at a position farthest from the coil 4 inside, the magnetic shield plate hardly attracts the magnetic flux generated by the coil 4 and does not adversely affect the detection efficiency. Further, the flange portions 12a-1, 12b-1 of the pipes 12a, 12b are attached to the flange portions 1a, 1b at both ends of the measuring pipe via the liquid contact rings 13a, 13b.
Since the magnetic shield plate 10 does not have any influence on the magnetic flux even if is connected, measurement efficiency is not impaired and stable measurement can always be performed.

Embodiment 2 FIG. FIG. 3 is a partially cut-away front view showing an electromagnetic flowmeter according to a second embodiment of the present invention. In the above-described first embodiment, the measuring tube both end flange portions 1a, 1b are shown.
Although the ring-shaped magnetic shield plate 10 is arranged on the outer surface of the above, in the second embodiment, the arc-shaped magnetic shield plate 10a shown in FIG.
10d arranged in a ring shape and assembled and fixed with, for example, an adhesive or the like makes it easier for the magnetic flux from the coil 4 to slightly flow to the magnetic shield plates 10a to 10d, but the same effect as the first embodiment. Is obtained.

[0015]

As described above, according to the first aspect of the present invention, the magnetic shield plate is provided on the outer surface of the flange portion at both ends of the measuring tube, and according to the first aspect of the invention, the inner surface of the flange portion at both ends of the measuring tube is provided. Since the magnetic shield plate is assembled, the magnetic shield plate is located farthest from the coil in the case, the magnetic flux generated by the coil is hardly attracted, and the detection efficiency is not adversely affected. Further, even if the flange portions of the pipe are connected to the flange portions at both ends of the measuring pipe, the magnetic flux is magnetically shielded by the magnetic shield plate and is not affected at all. Therefore, there is an effect that stable measurement can be always performed without impairing the measurement efficiency.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing an electromagnetic flowmeter according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the principle of an electromagnetic flow meter.

FIG. 3 is a partially cutaway front view showing an electromagnetic flow meter according to a second embodiment of the present invention.

FIG. 4 is a front view of a magnetic shield used in the second embodiment.

FIG. 5 is a partially cutaway front view showing a conventional electromagnetic flowmeter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measuring pipe 1a, 1b Measuring pipe both ends collar part 2 Fluid to be measured 4 Coil (magnetic field generating means) 5 Electrode 10 Magnetic shield plate 12a, 12b Piping 12a-1, 12b-1 Flange part

Claims (1)

[Claims] 1. A measuring pipe through which a fluid to be measured is passed, a magnetic field generating means for generating a magnetic field orthogonal to the fluid to be measured in the measuring pipe, and the measurement so as to measure an electromotive force generated by the action of the magnetic field. An electromagnetic flowmeter comprising: at least a pair of electrodes provided to face each other on the diameter of the tube; and a magnetic shield plate provided on both end flanges of the measurement tube.