JPH0318891Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to an electromagnetic flowmeter transmitter, and is an improvement that specifically eliminates the problems that occur when the distance between the surfaces of the electromagnetic flowmeter transmitter is shortened. This is what I did.

<Prior Art> FIG. 1 is a configuration diagram of an electromagnetic flowmeter transmitter according to the prior art. FIG. 1a shows its longitudinal section, and FIG. 1b shows its cross-section. As shown in the figure, a case 3 in which a conduit 2 with a lining 1 is integrated with a flange
An excitation coil 4 that forms a magnetic field is inserted and fixed between the conduit 2 and the case 3. When the fluid crosses the magnetic field B generated by the excitation coil 4, a voltage corresponding to the flow rate is generated at the detection electrodes 5a and 5b. Magnetic field B takes case 3 as its return path,
A portion also leaks to the external piping side of case 3. Furthermore, grounding flanges 6a and 6b for grounding the measurement liquid are fixed to the outside of the case 3, and together these flanges 6a and 6b form a transmitter. The axis connecting the detection electrodes 5a and 5b is the X-X' axis, the tube axis of the conduit 2 is the Z-Z' axis, and the X-
The axis perpendicular to both the X' axis and the Z-Z' axis is the Y-
Let it be the Y′ axis. The aperture of the transmitter is referred to as D, and the length of the transmitter in the axial direction is referred to as distance L between surfaces. The signal voltage corresponding to the flow rate generated in the fluid is detected by the detection electrodes 5a and 5b.
The closer the detection electrodes 5a, 5b are, the greater the influence is, and the farther away from the detection electrodes 5a, 5b, the smaller the influence. The sum of the voltages generated at each point in the fluid becomes the voltage generated between the detection electrodes 5a and 5b. The extent of the spread can be evaluated by knowing the electric field distribution generated in the fluid when a voltage is applied between the detection electrodes 5a and 5b.

FIG. 2 shows the electric field distribution generated in the measurement fluid when the transmitter is installed in the pipe and a potential difference is applied between the detection electrodes. Hereinafter, parts having the same functions as those in FIG. 1 will be denoted by the same numbers, and explanations will be omitted as necessary. When the transmitter shown in Fig. 1 is installed between the pipes 7 and 8 and a voltage is applied between the detection electrodes 5a and 5b, there is generally a voltage between the detection electrodes 5a and 5b in the measured fluid as shown in the figure. In addition, from the detection electrode 5a or 5b to the grounding flange 6a, 6b
There are also lines of electric force spanning the pipes 7 and 8.
If the inter-plane distance L of the transmitter is longer than the aperture D, the lines of electric force directed from the detection electrodes 5a to 5b will not reach the grounding flanges 6a, 6b or the pipes 7, 8, causing no error, but the inter-plane distance When L becomes shorter than the diameter D, as shown in the figure, some of the electric lines of force between the detection electrodes 5a and 5b reach the grounding flanges 6a and 6b and the pipes 7 and 8, resulting in span error and conductivity of the measured fluid. become influenced by.

In recent years, electromagnetic flowmeters have tended to be made smaller in pursuit of economic efficiency and weight reduction, and at the same time, there is also a tendency for high accuracy to be required. In order to achieve miniaturization, the distance L between the surfaces of the transmitter must be made smaller than the aperture D. However, simply the distance L between the surfaces
If D is made smaller than the aperture D, there will be a problem in that it will be affected by the span error and the conductivity of the fluid to be measured, as described above. In particular, since the piping may be a conductive conduit such as a cast iron pipe or an insulating conduit made of plastic, the span error will vary depending on the type of piping.

<Purpose of the invention> In view of the above-mentioned prior art, the present invention aims to eliminate span errors caused by changes in the type of mating piping and changes in the conductivity of the measured fluid that occur with downsizing.

<Configuration of the device> The configuration of the device that achieves this purpose is
In an electromagnetic flowmeter transmitter for measuring an electrolyte fluid whose inner surface is lined and has an inter-plane distance of less than 2 times, at least one pair of detection electrodes are arranged on the inner circumferential surface of the cross-section in the center of the inter-plane distance, and This electromagnetic flowmeter transmitter is characterized in that the distance between a pair of detection electrodes is less than 1/2 of the distance between surfaces.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 3 shows one embodiment of the present invention. In the figure, 9 _a-1 and 9 _b-1 and 9 _a-2 and 9 _b-2 are pairs of detection electrodes for detecting flow rate signals. Each detection electrode is fixed to the inner surface of the lining 1 in a plane containing the Y-Y' axis. Detection electrode 9 _a-
1 and 9 _b-1 or detection electrodes 9 _a-2 and 9 _b-2 form a pair, and the distance between each detection electrode is P. The value of P is selected to be smaller than the aperture D of the transmitter. FIG. 4 shows the electric field distribution formed in the measurement fluid when a voltage is applied between the detection electrodes 9 a-1 and 9 _b-1 in the configuration shown in FIG. 3. Distance P between detection electrodes 9 _a-1 and 9 _b-1
Since the diameter D is smaller than the diameter D, the distribution of the electric lines of force is localized, and the proportion of the lines of electric force extending to the pipe 7 or 8 is reduced. The rate of decrease is P/D, which is approximately equivalent to the case where the transmitter has an inter-plane distance of PL/D with respect to the inter-plane distance L of the transmitter. In other words, in order to make the influence of piping the same on the distance L between surfaces of the conventional transmitter, according to this embodiment,
This means that it is equivalent to a PL/D surface distance transmitter. In other words, the size can be reduced accordingly.

FIG. 5 is an experimental curve for determining the relationship between span error and distance between surfaces. The horizontal axis is the face-to-face distance of the transmitter expressed in aperture units, and the vertical axis is the face-to-face distance (expressed in aperture units) as the span error when the conductivity of the measuring fluid is changed from 200μ/cm to 20000μ/cm. It is expressed as a ratio, taking the case where L/D) is 1.1 as 1. Note that in this case, the distance P of the detection electrode is equal to the aperture D, which is the limit curve in this embodiment. As can be seen from this curve, as the interplanar distance (L/D) increases, the span error with respect to changes in conductivity tends to gradually decrease, and the error becomes completely zero when L/D=2.0. From the fact in this limit, in the case of an inter-plane distance twice the aperture, when the distance P between the detection electrodes is the aperture D, no span change occurs with respect to a change in conductivity. When the distance L between the surfaces is so short as to be equal to the aperture D, the transmitter can be made unaffected by changes in conductivity by setting P to half the aperture.

<Effects of the invention> As explained above in detail with the examples, according to the invention, span errors due to the inner surface condition of the mating piping or the conductivity of the measured fluid do not occur even between short surfaces.
Since it is possible to reduce costs, it is possible to realize an electromagnetic flowmeter transmitter with short dimensions and high precision, which has been difficult to realize in the past.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional electromagnetic flowmeter transmitter, Figure 2 is a diagram of electric field distribution in the measured fluid in the case of Figure 1,
Fig. 3 is a configuration diagram of this embodiment, Fig. 4 is an electric field distribution diagram in the measurement fluid in the case of Fig. 3, and Fig. 5 is a diagram showing the span error due to conductivity change with respect to the distance between the transmitter surfaces. be. 5a, 5b...Detection electrode, 6a, 6b...Grounding flange, 7, 8...Piping, 9 _a-1 , 9 _b-1 , 9 _{a-
2,9 b-2} ...Detection electrode, L...Distance between surfaces, D...
Aperture, P... Distance between detection electrodes.

Claims (1)

[Scope of utility model registration request] In an electromagnetic flowmeter transmitter for measuring an electrolyte fluid, the inner surface is lined and has a distance between surfaces less than twice the diameter, and at least one pair of detection electrodes are arranged on the inner peripheral surface of the cross section at the center of the distance between the surfaces. An electromagnetic flowmeter transmitter characterized in that the distance between the pair of detection electrodes is set to 1/2 or less of the distance between the surfaces.