JPH0226032Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a liningless electromagnetic flowmeter (hereinafter abbreviated as electromagnetic flowmeter as necessary), and in particular to an electromagnetic flowmeter with a short distance between surfaces. Concerning useful ideas for use in

<Prior art> In conventional electromagnetic flowmeters, the signal voltage generated in the conduit in response to the flow rate is generally short-circuited in the conductive conduit, so to prevent this, the inner surface of the conduit is lined with an insulating lining material. has been done. However, recently, electromagnetic flowmeters without linings have been devised to prevent accidents caused by deformation of the lining material. An example of such a conventional electromagnetic flowmeter is shown in FIG. FIG. 1a shows the configuration of an electromagnetic flowmeter including a cross section of a conductive conduit, and FIG. 1b is a side view showing the right side of the conductive conduit.

In FIG. 1, a fluid to be measured 2 is connected to a conductive conduit 1.
is filled, and a magnetic field B is applied across the conductive conduit 1 (the magnetic field generating means is not shown). When the fluid to be measured 2 flows, a signal voltage is generated at the measurement electrodes 3a and 3b. This signal voltage is applied to the feed amplifier 4
It is applied to the non-inverting input terminals of signals a and 4b and is amplified. The voltage appearing at the output ends 5a, 5b causes a current to flow to the ground electrode 8 via the power supply electrodes 7a, 7b, which are fixed to the conductive conduit 1 near the measuring electrodes 3a, 3b and connected to each other by connecting wires 6a, 6b. flowing,
A potential distribution is formed in the conductive conduit 1. The potential near the measurement electrode of the potential distribution formed in this way is determined by the tube potential electrodes 9a, 9b fixed to the conductive conduit 1 between the measurement electrodes 3a, 3b and the power supply electrodes 7a, 7b.
is detected and fed back to the inverting input terminals of the feed amplifiers 4a and 4b, and is stabilized in a balanced state. Power supply electrode 7
a, 7b have a length l parallel to the tube axis of the conductive conduit as shown in FIG. 1b. Similarly, the ground electrode 8 is also arranged parallel to the tube axis of the conductive conduit 1 like the power supply electrodes 7a and 7b. Therefore,
The current given to the power supply electrodes 7a, 7b by the power supply amplifiers 4a, 4b is divided in parallel between the power supply electrodes 7a, 7b and the upper and lower ground electrodes 8. Therefore, the potential distribution is studied as a two-dimensional problem in a cross section perpendicular to the pipe axis of the conductive pipe 1. However, this does not pose a particular problem as a two-dimensional problem when the distance L between the surfaces of the electromagnetic flowmeter (approximately equal to the distance between the surfaces of the conductive pipe) is long, but when the distance L between the surfaces becomes short, Potential of the tube wall near the ends 1u and 1l of the conductive pipe 1 and the measured fluid 2 near the ends 1u and 1l
potentials do not match, a current crosses the tube wall into the fluid to be measured, and the signal voltage is affected by the conductivity of the fluid to be measured.

<Purpose of the invention> In view of the above-mentioned prior art, an object of the present invention is to obtain a liningless electromagnetic flowmeter that does not cause errors even between short surfaces.

<Configuration of the invention> The configuration of the present invention to achieve this object is to provide a liningless electromagnetic flowmeter in which the same potential distribution as the potential generated inside the conductive conduit through which the fluid to be measured flows is formed in the conductive conduit. , a measurement electrode fixed to the conductive conduit that detects a signal voltage corresponding to the flow rate of the fluid to be measured; a main power feeding electrode fixed to the conductive conduit near the measurement electrode; and an auxiliary power supply electrode disposed near the end face of the conductive pipe line with the power supply electrode sandwiched in the axial direction of the conductive pipe line, and the electric potential generated in the fluid to be measured near the end face is According to the present invention, power is supplied to the auxiliary power supply electrode so that the potential of the tube wall at the end face of the conductive conduit becomes large.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings. Note that parts having the same functions as those in the prior art are denoted by the same reference numerals, and redundant explanations will be omitted.

FIG. 2 shows a first embodiment of the invention. In FIG. 2, only one side of the conductive conduit is shown, but since both sides have the same configuration, the opposite side is omitted. The measuring electrode 3a is fixed at the center of the conductive conduit 1, and above and below it, main power supply electrodes 10a and 11a corresponding to the power supply electrode 3a in FIG. It is fixed to conduit 1. The upper and lower main power feeding electrodes 10a and 11a are connected by a connecting wire 6a and held at the same potential.
In the vicinity of the upstream and downstream end surfaces 1u and 1l of the conductive conduit 1 across the main power supply electrodes 10a and 11a, there are main power supply electrodes 10 on the same straight line as the main power supply electrodes 10a and 11a.
Auxiliary power supply electrodes 12a, 1 are separated from a, 11a.
3a, 14a and 15a are fixed to the conductive conduit 1. And auxiliary power supply electrodes 12a, 13
a, 14a, and 15a are located at equal distances from the measurement electrode 3a. These auxiliary power supply electrodes 12a, 1
3a, 14a, and 15a are connected by connection lines 16a, 17a, and 18a, respectively, and held at the same potential. The measurement electrode 3a and the non-inverting input end of the amplifier 4a are connected, and the inverting input end is connected to the tube potential electrode 9a. The output end 5a of the amplifier 4a is connected to the main feeding electrode 11a.
A tube potential electrode 19a for detecting the tube potential at the end of the conductive tube 1 is fixed to the conductive tube 1 near the auxiliary power supply electrode 12a. One end of the tube potential electrode 19a and a potentiometer 20a are connected, and the other end of the potentiometer 20a is connected to a common C of the circuit. potentiometer 20a
is a midpoint 21a for extracting the attenuated voltage.
is provided. Measuring electrode 3a and amplifier 22a
The non-inverting input terminal of the potentiometer 20a is connected to the non-inverting input terminal of the potentiometer 20a, and the inverting input terminal thereof is connected to the midpoint 21a of the potentiometer 20a. The output terminal of the amplifier 22a is connected to the auxiliary power supply electrode 1
It is connected to 2a. With the above configuration, the amplifier 22a supplies power to the auxiliary power supply electrode 12a so that the potential near the auxiliary power supply electrode 12a is attenuated by the potentiometer 20a and the potential of the measurement electrode 13a becomes equal. Operate.
In other words, the potential of the auxiliary power supply electrode 12a is controlled to be higher than the potential of the measurement electrode 3a. Connecting wires 16a and 17 are connected between the auxiliary power supply electrodes.
a and 18a, the potential of the tube wall near the ends 1u and 1l of the conductive pipe 1 is relatively high compared to the potential of the fluid 2 to be measured near the ends 1u and 1l. becomes.

Next, it will be explained that the electromagnetic flowmeter configured as described above is not affected by the conductivity of the fluid to be measured.
FIG. 3 is an explanatory diagram illustrating the operation of the embodiment shown in FIG. 2. Now, let P be an arbitrary point in the cross section of the conductive pipe including the measurement electrode, and define this as conductive pipe 1.
Consider the potential Up (Z) at each point when moving in the direction of the tube axis (referred to as the Z axis). Conductive conduit 1
is lined with an insulating material, and the distance L between the surfaces of the conductive conduit 1 is long, the potential at point Z
Up (Z) also exists outside the end face of the conductive conduit like a curve. A weighting function that indicates the proportion of the contribution to the electrode when a unit signal voltage is generated inside the conduit exists both upstream and downstream of the end face of the conductive conduit, and also prevents leakage of the magnetic field in the axial direction. Because there is. Next, if an earth ring is installed on the end face of the conductive pipe, or if the inner surface of the attached pipe is made of conductive material, the potential distribution Up (Z) of the conductive pipe is as shown by the curve. The potential distribution becomes zero at the end face. This is because the signal voltage is short-circuited at the ground ring or the attached piping. For this reason, the potential distribution Up(Z) changes depending on the degree of conductivity of the inner surface of the attached pipe, and an error occurs when the inter-surface distance L is shortened. Therefore, in this embodiment, as shown by the curve, a potential higher than the potential in the case of insulating lining is supplied from the amplifier 22a to the auxiliary power supply electrodes 12a, 13a, 14a and 15a. In this way, among the two areas surrounded by the curves and, in area A, the potential of the conductive pipe 1 is higher than the signal voltage, so a current flows from the conductive pipe 1 to the fluid to be measured 2, and in the area B, the electric potential of the conductive pipe 1 is higher than the signal voltage. Conversely, a current flows from the fluid to be measured 2 to the conductive conduit 1 . Therefore, by adjusting the potential to the inverting input terminal of the amplifier 22a with the potentiometer 20a in FIG. There is no current flowing in or out between the measured fluid 2 and the measured fluid 2. Therefore, it does not depend on the conductivity of the fluid to be measured or the contact resistance between the conductive pipe line 1 and the fluid to be measured 2. Note that the potential Up (Z) at point P is the main power supply electrode 10.
The potential distribution is large near points a and 11a, and close to zero near the ground electrode 8, but the potential distribution in FIG. 3 shows a similar tendency no matter where the point P is located.

FIG. 4 shows a second embodiment of the invention. In FIG. 2, the main power supply electrodes 10a, 11a and the auxiliary power supply electrodes 12a, 1 are located on the same line as the tube axis direction of the conductive conduit 1.
3a, 14a and 15a were arranged to set the potentials of the main power supply electrode and the auxiliary power supply electrode to different values,
In the case of FIG. 4, main power supply electrodes 10a, 11a and auxiliary power supply electrodes 23a, 24a, 25a and 26a
Although the potential is the same as that of the auxiliary power supply electrodes 23a, 2
4a, 25a and 26a to the main power supply electrode 1
By bringing the electrodes closer to the upper and lower ground electrodes 8 than 0a and 11a, the potential of the end faces 1u and 1l of the conductive conduit 1 is made higher than the potential of the fluid to be measured, thereby achieving the same purpose as in the case of Fig. 2. ing. In addition, 27a,
28a, 29a and 30a are connection lines for bringing the auxiliary power supply electrodes 23a, 24a, 25a and 26a and the main power supply electrode to the same potential, respectively.

<Effects of the invention> As described above in detail with the embodiments, according to the invention, by providing an auxiliary power supply electrode in the conductive conduit and applying a high potential to it, the conductivity of the fluid to be measured and the A liningless electromagnetic flowmeter between short surfaces can be realized without being affected by contact resistance between the measured fluid and the conductive pipe.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of a conventional liningless electromagnetic flowmeter, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is an explanatory diagram illustrating the operation of Fig. 2. FIG. 4 is a block diagram showing another embodiment of the present invention. 1... Conductive pipe line, 2... Fluid to be measured, 3a,
3b...Measurement electrode, 4a, 4b...Amplifier, 8...
...Ground electrode, 9a...Tube potential electrode, 10a, 11
a... Main power supply electrode, 12a, 13a, 14a, 1
5a...Auxiliary power supply electrode, 22a...Amplifier, 23
a, 24a, 25a, 26a...Auxiliary power supply electrodes.

Claims (1)

[Scope of utility model registration request] In a liningless electromagnetic flowmeter in which the same potential distribution as that generated inside the conductive pipe through which the fluid to be measured flows is formed in the conductive pipe, the signal voltage corresponding to the flow rate of the fluid to be measured is detected. a measurement electrode fixed to a conductive conduit, a main power supply electrode fixed to the conductive conduit near the measurement electrode, and a main power supply electrode sandwiched between the main power supply electrode in the axial direction of the conductive conduit. an auxiliary power supply electrode disposed near the end face of the conductive conduit, the electric potential of the pipe wall at the end face of the conductive conduit being greater than the potential generated in the fluid to be measured near the end face; A liningless electromagnetic flowmeter that supplies power to the auxiliary power supply electrode so that.