JPS5815120A - Transmitter of electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To eliminate the leakage through sealing and to improve relability with simpe construction by disposing a magnetic field generator which generates a magnetic field of the frequency differeing from commercial frequencies in such a way as to intersect orthogonally with a conduit and providing one piece of electrode for measurement to a conduit. CONSTITUTION:A magnetic field generator 8 which generates a square wave magnetic field of the frequency, for example, 1/8 the commercial frequency is disposed in such a way so that the magnetic field thereof intersects orthogonally with a conduit 1 in which fluid flows. One piece of measuring electrode 2 is mounted to the conduit 1, which electrode 2 is connected to the non-inversion input terminal of a differential amplifier 6. Commercial frequency noise ecN and electromagnetic induction noise eiN are removed by the converter connected to the terminals 7, 7a on the output side of the amplifier 6, and only the flow rate signal is drawn out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic flowmeter transmitter, and has been modified to simplify the structure and improve reliability.

Part 1 (2) shows the main parts of a conventional electromagnetic flowmeter transmitter. As shown in the figure, a pair of measuring electrodes 2, 2a are attached to the conduit 1), and this measuring electrode 2.2m is attached to the terminals 3, 3al.
It is connected to an amplifier (not shown) via the power supply. The magnetic field generator 4 generates a sinusoidal magnetic field at a commercial frequency, and is arranged so that the direction of the magnetic field is perpendicular to the straight line connecting the tube axis of the conduit l and the measurement electrodes 2.2a. Therefore, a flow rate signal proportional to the flow rate is sent out from the measurement electrodes 2, 2a. Furthermore, evaluating the conventional technique #f based on the equivalent circuit shown in the tXz diagram, the fluid in one circle of the conduit has not only the flow voltage e@, e@ due to the magnetic field of the magnetic field generator 4, but also commercial frequency noise due to the commercial power supply. (Common So-P noise) eCN is also generated. Therefore, through the wetted impedance 2 between the measuring electrode 2.2a and the fluid and the resistance r of the fluid itself, m' voltage eS and commercial frequency noise Ccj* flow to the measuring electrode 2K.
However, a flow voltage -cs and a commercial frequency noise eCN are generated at the measurement electrode 2a. When the measurement electrode 2 is connected to a high input impedance buffer amplifier 5 connected to the terminal 3, the measurement electrode 2 is connected to the resistors R1, R2, and R3 for removing common mode noise.

Similarly, the measurement electrode 2a is connected to the non-inverting input terminal of the differential y-Zoro connected to the electrode 2a.
The inverting input terminal of the differential amplifier 6 is connected to the inverting input terminal of the differential amplifier 6 through the inverting input terminal. In addition, a converter (not shown) that converts the *i flow rate signal from the electromagnetic flowmeter transmitter into a unified current signal or -9 pulse train signal is connected to the output side terminals 7 and 7a of the differential amplifier 6. be done. Therefore, the rt generated in the measurement electrodes 2 and 2a, respectively.
A flow rate signal corresponding to the voltage 2eB of the difference between t* voltage as and -esO is sent from the differential amplifier 6 to the converter, and the commercial frequency noise elcN is input as common mode noise to the differential amplifier 6. are canceled out and removed.

By the way, in the conventional technique, two measurement electrodes 2, 2a are used.
is attached to the conduit 1, which not only increases the chance of fluid leaking through this attachment part, but also requires a complicated sealing structure in which the measurement electrode 2.2a is attached to the conduit 1 to ensure a fluid seal. I had to prepare in place.

In view of the above prior art, it is an object of the present invention to provide an electromagnetic flowmeter transmitter that has a low probability of seal leakage, has a simple structure, and is highly reliable. The configuration of the present invention that achieves this object includes a magnetic field generating device that generates a magnetic field at a frequency different from the commercial frequency so as to be orthogonal to a conduit through which fluid flows, and one measurement electrode attached to the conduit. and obtaining a flow signal generated between the measurement electrode and a reference potential point by the fluid and the magnetic field.

Below, the ritual N of the present invention will be explained in detail based on the drawings. Note that parts that are the same as those in the prior art are given the same numbers and redundant explanations will be omitted.

FIG. 3 shows an equivalent circuit of an embodiment of the present invention.

As shown in the figure, the magnetic field generating device 8 generates a rectangular wave magnetic field with one frequency being a commercial frequency.

This rectangular wave magnetic field is arranged so as to be orthogonal to the conduit 1. Further, one measuring electrode 2 is attached to the conduit IK, and this measuring electrode 2 is connected to the non-inverting input terminal of the differential amplifier 6. At this time, the inverting input terminal of the differential amplifier 60 is in contact with the liquid at a location where no electromotive force is generated. In other words, the differential amplifier 6 only sends out a signal corresponding to the voltage input thereto, but does not have the function of removing noise.

Therefore, not only the flow voltage e8 generated by the rectangular wave magnetic field but also the commercial frequency noise ec generated due to the commercial power supply
Electromagnetic induction noise eiN generated due to x and temporal changes in the rectangular wave magnetic field (changes at the time of rise and fall of the rectangular wave magnetic field) is also input to the differential amplifier 6, and as a result, this amplifier 6 The flow rate signal that is the output includes commercial frequency noise ecN and electromagnetic induction noise eiN. therefore,
A flow signal containing noise is input to a converter (not shown) connected to the terminals 7 and 7a. However, when the electromagnetic flowmeter oscillator is of a low frequency excitation type as in this embodiment, the converter performs all signal sampling at the point when the rectangular wave magnetic field (excitation magnetic field) is stabilized and the timing is synchronized with the commercial frequency noise. As a result, commercial frequency noise ecl (and electromagnetic induction noise eiN) can be removed, only the flow rate signal can be extracted, and accurate flow rate measurement can be performed.

The results of actual flow rate measurements according to this embodiment are shown in FIGS. 4 and 5. Figure 4 shows the specified flow rate as 100
Output error (q
6 rate).

From this characteristic, the output error is ±0.6 ("% rate
). Also shown in Figure 5 is 70-1/
- Output display (0
UTPUT), and it can be seen from this characteristic that the error is extremely small.

In the above embodiment, the magnetic field generator 8 generates a low frequency rectangular wave magnetic field, but it is sufficient for the magnetic field to be generated for measurement as long as the frequency is different from the commercial frequency. By using a magnetic field with a frequency different from the trench commercial frequency, it is possible to extract only the flow rate signal using a converter. In addition, as shown in FIG. 10, the inverting input terminal of the differential amplifier 6 is in contact with liquid through a connected mating pipe that has electrical continuity with the fluid, and as shown in FIG. 11, the electromagnetic flow rate This may be done with the liquid contact flange 10 attached to the end face of the 7-lange of the meter transmitter.Also, if the fluid is grounded, the inverting input electron of the differential anzoro may be grounded as shown in Figure 12. . Furthermore, the measurement electrode 2 is not limited to a point electrode as shown in FIG. 1, but may also be a linear electrode facing the inner peripheral surface of the conduit 1 as shown in FIGS. 6 and 7, or a wire electrode as shown in FIG. As shown in FIG.
It may also be a capacitive sensing electrode embedded therein.

Furthermore, the 91st i! ! The code in the middle, 9, indicates No-Using.

As specifically explained above in conjunction with the embodiments, according to the present invention, only one measuring electrode is attached to the conduit, which simplifies the structure, facilitates manufacturing, and reduces costs.

The probability of seal leakage at the part where the measurement electrode is attached is reduced and reliability is improved. Furthermore, since the electromagnetic flowmeter was excited by a magnetic field with a frequency different from the commercial frequency, by connecting a converter to the electromagnetic flowmeter oscillator, only the flow rate signal corresponding to the flow rate can be extracted, allowing accurate flow rate measurement.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the main parts of a conventional electromagnetic flowmeter transmitter.
FIG. 2 is a circuit diagram showing the equivalent circuit. FIG. 3 is a circuit diagram showing the equivalent circuit of the embodiment of the present invention. FIG. 4 is a characteristic diagram showing the flow rate-output error characteristic of this embodiment. 1 is a characteristic diagram showing its flow rate-output display characteristics, and FIGS. 6 to 9 show other examples of measurement electrodes used in this example. 1 is a conduit, 2.2a is a measurement electrode, 4.8 is a magnetic field generator. Patent Applicant Hokushin Electric Manufacturing Co., Ltd. Representative Patent Attorney Mr. Motogata (and 1 other person) Figure 3 Display Figure 4 Figure 5

Claims (1)

[Claims] A magnetic field generating device that generates a magnetic field with a frequency different from the commercial frequency so as to be orthogonal to a conduit through which a fluid flows, and a measuring electrode attached to the conduit, and a measuring electrode and a measuring electrode attached to the conduit. An electromagnetic flowmeter transmitter characterized in that it obtains a flow rate signal generated between reference potential points.