JPH07243885A - Dc excitation electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To obtain an electromagnetic flowmeter with a better polarization voltage noise resistance characteristic by providing an electrode with a conductivity smaller than that of a measuring fluid so as to allow the prevention of the generation of a polarization voltage. CONSTITUTION:A DC magnetic field generation means 11 employs a permanent magnet. An insulating measuring pipe 12 into which a conductive measuring fluid flows comprises a resin material. The resin material herein used is a polyvinylchloride resin, acrylnitrile butadiene styrene resin, polycarbonate resin etc. An electrode 13 uses the same resin as that of the measuring pipe mixed with a conductivity oriented material to adjust a volume intrinsic resistance in a range to be larger than at least that of the measuring fluid. The conductivity-oriented material herein used is carbon fiber, carbon powder, metal powder or the like. The electrode 13 is formed with the conductivity smaller than that of the measuring fluid to allow the prevention of the generation of a polarization voltage thereby obtaining a flow rate free from any drift.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC excited electromagnetic flowmeter having good noise resistance.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of a main part of a conventional example which has been generally used. For example, the actual exploitation 62-
No. 49726, Japanese Patent Application No. 60-142322, "Electromagnetic Flowmeter", filed on September 18, 1985.

In the figure, reference numeral 1 is a measuring tube made of cylindrical ceramics. Reference numeral 2 is an electrode arranged in the measuring tube 1. Reference numeral 3 is a DC exciting coil provided on the outer peripheral surface of the measuring tube 1. A housing 4 is provided to cover the DC exciting coil 3.

In the above structure, the DC exciting coil 3 is excited to extract an electromotive force proportional to the flow rate of the measuring fluid from the electrode 2 to detect the flow rate of the measuring fluid.

[0005]

However, in such a device, when the DC exciting coil 3 is excited, a DC voltage is induced in the electrode 2. Here, the problem is that when the conductivity of the electrode 2 is higher than the conductivity of the measurement fluid, a polarization voltage (noise voltage) is generated at the interface of the electrode 2 and causes a drift.

The present invention solves this problem. An object of the present invention is to provide a DC excitation electromagnetic flowmeter having good polarization voltage noise resistance.

[0007]

In order to achieve this object, the present invention relates to a measuring tube into which a conductive measuring fluid is introduced and a magnetic field for generating a DC magnetic field orthogonal to the axial direction of the measuring tube. DC excitation electromagnetic flowmeter comprising a generating means and an electrode provided in the measurement tube in a direction orthogonal to the axial direction of the measurement tube and the direction of the DC magnetic field to detect an electric signal proportional to the flow rate of the measurement fluid. In the above, there is provided a direct-current excitation electromagnetic flowmeter characterized by comprising an electrode having a conductivity smaller than that of the measurement fluid so as to prevent generation of a polarization voltage.

[0008]

In the above structure, since the electrode having the electric conductivity smaller than that of the fluid to be measured is formed, the generation of the polarization voltage can be prevented. Hereinafter, detailed description will be given based on examples.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the essential parts of an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line A--A of FIG. 1 and 2, the same symbols as those in FIG. 4 represent the same functions. Only parts different from FIG. 4 will be described below.

Reference numeral 11 is a DC magnetic field generating means. In this case, a permanent magnet is used. Reference numeral 12 is an insulating measuring tube into which a conductive measuring fluid is introduced. In this case, it is made of a plastic material. PVC (polyvinyl chloride) resin, ABS (acrylonitrile butadiene styrene) resin, polycarbonate resin, PPS (polyphenyl sulfide) resin, nylon resin, and fluorine resin are used.

Reference numeral 13 is an electrode. In this case, the same resin as the measuring tube 12 is mixed with the conductivity imparting material shown below,
In this case, the volume resistivity is adjusted to 10 ⁴ to 10 ⁷ Ωcm. Examples of the conductivity imparting material include carbon fiber, carbon powder, carbon black, graphite powder, potassium titanate, metal powder (Al, N
i, Fe, Ag, Pt, stainless steel) and metal fibers (Al, Ni, Fe, Ag, Pt, stainless steel) are applicable.

For example, as an example of a combination of an insulating plastic and a conductivity-imparting material, when about 10% by weight of carbon fiber is mixed with polycarbonate resin, 10
A conductive electrode of ⁵ Ωcm can be created. Further, if the composition ratio of the conductivity-imparting material to be mixed with the electrode 13 is appropriately selected, the volume resistivity can be adjusted to be larger than 10 ⁴ Ωcm.

However, the volume resistivity is preferably set to 10 ⁴ to 10 ⁷ Ωcm as the signal source resistance so that the signal source impedance of the input circuit does not become too high. If the volume resistivity is at least larger than the volume resistivity of the fluid to be measured, and the volume resistivity is set to be 10 ⁷ Ωcm even if it is large, an electrode that does not cause polarization can be obtained. Will be resolved.

For example, when the measurement fluid is tap water, tap water has a volume resistivity of 10 ⁴ Ωcm. Therefore, if the volume resistivity of the electrode 13 is adjusted to be 10 ⁴ to 10 ⁷ Ωcm, the polarization will change. An electrode that does not occur is obtained, and the drawbacks of the electrode of the conventional DC excitation electromagnetic flowmeter are eliminated.

In the above structure, since the electrode 13 having a conductivity lower than that of the fluid to be measured is configured, it is possible to prevent the polarization voltage from being generated. As a result, it is possible to obtain a DC-excited electromagnetic flowmeter that does not cause a drift due to the generation of a polarization voltage (noise voltage), and it is possible to expand the usable fields of the DC-excited electromagnetic flowmeter.

The base material of the electrode 13 is used as the measuring tube 12
By using the same material as the base material of
The polymer binds across the boundary between and. As a result, the electrode 1
A DC-excited electromagnetic flowmeter can be obtained in which there is no risk of leakage of the measured liquid due to defective sealing in the three parts.

Further, since the permanent magnet is used for the direct current excitation, the electric power consumed for the excitation becomes unnecessary, and the direct current excitation electromagnetic flowmeter with extremely low power consumption can be obtained.

FIG. 3 is an explanatory view of the essential structure of another embodiment of the present invention. In this embodiment, the electrode 21 is made of silicon carbide S.
It is composed of iC. The volume resistivity of silicon carbide SiC is 10 ⁵ Ωcm, and the volume resistivity is 10 ⁴ to 10 ⁷
Within the range of Ωcm.

As a result, it is not necessary to prepare the insulating plastic and the conductivity-imparting material, and it is possible to obtain the DC excitation electromagnetic flowmeter in which the manufacturing cost of the electrode 21 is low. In addition, in the above-mentioned embodiment, although it was described that one kind of the conductivity imparting material was used, the present invention is not limited to this, and for example, two kinds or more may be used. In short, it is only necessary to obtain the required volume resistivity.

In the above embodiment, the measuring tube 1
2 It was explained that the whole was composed of plastic, but it is not limited to this, for example, a metal pipe lined with plastic, or a metal pipe lined with rubber (polyurethane rubber, chloroprene rubber, EPDM rubber). But good. At this time, the electrode 13 is structured to be electrically insulated from the metal tube.

The measuring tube 12 may be made of a ceramic material. For example, the measuring tube 12 is made of silicon nitride Si ₃ N ₄
And a small amount of titanium carbide TiC is contained in the electrode part,
The volume resistivity can be adjusted within the range of 10 ⁴ to 10 ⁷ Ωcm.

[0022]

As described above, the present invention provides a measuring tube into which a conductive measuring fluid is introduced, a magnetic field generating means for generating a DC magnetic field orthogonal to the axial direction of the measuring tube, and the above-mentioned measurement. Generation of a polarization voltage in a direct current excitation electromagnetic flowmeter provided with an electrode provided in the measuring pipe in a direction orthogonal to the axial direction of the pipe and the direction of the direct current magnetic field and detecting an electric signal proportional to the flow rate of the measuring fluid. In order to prevent the above, a DC excitation electromagnetic flowmeter is constructed which is provided with an electrode having a conductivity lower than that of the measurement fluid.

As a result, since the electrode having the electrical conductivity smaller than that of the fluid to be measured is constructed, the generation of the polarization voltage can be prevented, and the drift caused by the generation of the polarization voltage (noise voltage) does not occur. Is obtained.

Therefore, according to the present invention, it is possible to realize a DC excitation electromagnetic flowmeter having a good polarization withstand voltage noise characteristic.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram of a main part configuration of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a configuration of a conventional example that is generally used in the past.

[Explanation of symbols]

 11 ... DC magnetic field generating means 12 ... Measuring tube 13 ... Electrode 21 ... Electrode

Claims (1)

[Claims] 1. A measuring tube into which a conductive measuring fluid is introduced,
Magnetic field generating means for generating a DC magnetic field orthogonal to the axial direction of the measuring tube, and proportional to the flow rate of the measuring fluid provided in the measuring tube in a direction orthogonal to the axial direction of the measuring tube and the direction of the DC magnetic field. A DC excitation electromagnetic flowmeter having an electrode for detecting an electric signal to be applied, characterized in that it is provided with an electrode having a conductivity smaller than that of the measurement fluid so as to prevent generation of a polarization voltage. Electromagnetic flow meter.