JPS6139931Y2 - - Google Patents

Description

[Detailed explanation of the idea]

1. Technical Field of the Invention The present invention relates to an electromagnetic flowmeter, and relates to an improvement of an electromagnetic flowmeter that measures fluids with large variations in flow velocity. 2. Prior Art A conventional example of this type of electromagnetic flowmeter is shown in Fig. 1. A conventional low frequency excited electromagnetic flowmeter is composed of an electromagnetic flowmeter detector 1 and an electromagnetic flowmeter converter 6.
A pair of excitation coils 2a, 2a' to 1 receive excitation power from a low frequency excitation power generator 11 which is activated by a synchronization signal from a synchronization signal generator 10 which transmits a synchronization signal of a predetermined frequency within the converter 6. Counter electrode 3
A magnetic flux 13 is applied to the measuring tube 3 having a magnetic field a, and a signal electromotive force proportional to the flow rate of the fluid flowing inside the measuring tube 3 is extracted from the electrode 3a. In the figure, 1a is an outer casing, 3b is an insulating lining, 4 is a signal electromotive force line, 5a is an excitation line, and 12 is a power source. A typical waveform of low frequency excitation is a square wave, and the signal electromotive force from the detector 1 has almost the same waveform as the excitation magnetic flux.The signal is amplified by the preamplifier 7 and set in advance by the span setting device 8. The measurement span is switched to the measured span and inputted to the converter with synchronous sampler 9, and the signal from the synchronous signal generator 10 samples the part A of the signal waveform where the transient phenomenon disappears as shown in FIG. 2, and this sampling value is set. The output signal 1 of the electromagnetic flowmeter is converted into a span flow signal.
Output as 4. 3 Problems with the conventional technology Conventional low-frequency excitation electromagnetic flowmeters use first-order differentiation or second-order A magnetic flux whose differential is zero is used. The rising speed of magnetic flux tends to slow down as the diameter increases, so the excitation frequencies of currently commercially available electromagnetic flowmeters are 3.125, 6.25,
12.5Hz is the mainstream. Although it is possible to increase the frequency by changing the voltage and current that are the excitation conditions for the coil, and the magnitude of the winding resistance of the excitation coil, this will soon reach its limit, and the size of the electromagnetic flowmeter detector will increase. There was a problem in that the design of the excitation power supply became difficult. 4. Purpose of the invention The purpose of the invention is to provide an electromagnetic flowmeter that is approximately the same size as a conventional electromagnetic flowmeter detector and is capable of measuring the flow rate of a fluid containing rapid pulsations in the fluid being measured. With the goal. 5. Structure of the invention In addition to the main excitation coil, this invention arranges a sub-excitation coil with the coil head closer to the electrode than the main excitation coil, and the main excitation coil and the sub-excitation coil are arranged in accordance with the set measurement span. An excitation coil connector is provided to selectively connect the electrodes to a low-frequency excitation power generator, and the magnetic flux density near the electrodes is made higher when measuring low flow velocity regions than when measuring high flow velocity regions. 6 Embodiment of the invention An electromagnetic flowmeter according to an embodiment of the invention is shown in Fig. 3.
The electromagnetic flowmeter detector 21 is provided with main excitation coils 2a and 2a' inside an outer casing 21a as in the conventional case, and furthermore, a pair of coil heads are connected to the main excitation coils 2a and 2a'. A pair of sub-excitation coils 22 and 22' are provided adjacent to the electrode 3a. The electromagnetic flowmeter converter 26 is provided with a span setting device 28 with a span information transmitter next to the preamplifier 7, and the excitation power from the low frequency excitation power generator 11 is set in advance based on the span information from the span setting device 28. Main excitation coil 2 according to a prescribed pattern
An excitation coil connector 25 is provided to selectively connect to the sub-excitation coils 22, 22'. 5a and 5b are excitation lines of the main excitation coils 2a, 2a' and the sub-excitation coils 22, 22', respectively. Other elements are the same as in FIG. In the electromagnetic flowmeter of the embodiment of the present invention configured as described above, the synchronization signal of a predetermined frequency from the synchronization signal generator 10 causes the low frequency excitation power generator 11 to
generates square wave excitation power at a predetermined frequency. On the other hand, when the measurement span is set in the span setting device with span information transmitter 28, this span information is input to the excitation coil connector 25, and the span information is inputted to the excitation coil connector 25.
is a low frequency excitation power generator 1 based on predetermined span information, that is, a pattern corresponding to the flow velocity range.
1 to the main excitation coils 2a, 2.
a' and the slave excitation coils 22, 22'. A magnetic flux whose first-order differential or second-order differential is zero, generated by these excitation coils, is applied to the fluid, and a signal electromotive force is extracted from the pair of electrodes 3a. This signal electromotive force has almost the same waveform as the excitation magnetic flux, and is amplified by the preamplifier 7, switched to a preset measurement span by the span setting device 28 with a span information transmitter, and then transferred to the converter 9 with a synchronous sampler. The part A shown in FIG. 2 is sampled by the signal from the synchronous signal transmitter 10, and this sampling value is converted into a flow rate signal of a set span and output signal 14 of the electromagnetic flowmeter.
is output as Low flow velocity region, e.g. flow velocity of 0 to 0.3 m/S, 0
〜0.4m/S…0〜1m/S Since the fluid flow is relatively axially symmetrical at the tip, it includes a pair of electrodes 3a shown in FIG. In terms of measurement accuracy, if the magnetic flux is symmetrical in a plane that includes the straight line XX' connecting the pair of electrodes 3a and is perpendicular to the plane of the paper, and in a plane that includes the straight line YY' that is perpendicular to the line XX' and is perpendicular to the plane of the paper in the cross section, There is no problem (provided that the actual flow is calibrated using this kind of magnetic flux distribution). Therefore, if the magnetic flux near the electrodes where a large signal electromotive force is generated despite the small excitation current is strengthened, a large electromotive force will be generated because the "weighting function" near the electrodes is large. Also, when the flow velocity is low, rapid pulsations with high frequencies are less likely to occur. Therefore, even if the signal electromotive voltage is increased by increasing the magnetic flux density in the vicinity of the electrode, almost no error occurs. Based on the above-mentioned flow characteristics at low flow speeds, the electromotive force is increased by exciting the sub-excitation coils 22 and 22' to increase the magnetic flux density near the electrodes at low flow speeds, and the excitation current is lower at high flow speeds. A sufficient signal electromotive voltage can be obtained even if the excitation current is made to be about the same as that of the excitation current, and the magnetic flux waveform rises sufficiently even if the excitation frequency is higher than that of conventional commercially available products. On the other hand, when the flow velocity is high, the peak of the fluid flow is also disturbed and rapid pulsations tend to occur. Straight line in Figure 4
XX') is switched to a so-called functional magnetic field that is close to a magnetic field distribution in which the strength of the magnetic field increases as it moves away from each point toward the inner wall of the measuring tube 3 to cancel out the influence of the "weighting function", and the flow velocity distribution To prevent measurement errors due to variations in the in this case,
Since the magnetic field strength near the electrode is the weakest, the generated electromotive force is reduced, but since the flow velocity is high, the generated electromotive force is correspondingly large, so there is no problem in measurement. Therefore, in the electromagnetic flowmeter according to the present invention, the excitation coil connector 25 selectively connects the main excitation coils 2a, 2a' and the sub-excitation coils 22, 22' according to the excitation pattern shown in the table below depending on the magnitude of the flow velocity. Let's do it.

[Table] By changing the magnetic field distribution between the low flow rate region and the high flow rate region using the pattern shown above, the disadvantage of conventional low frequency excitation electromagnetic flowmeters, ``difficulty in measurement including fast pulsations in the fluid,'' can be avoided. can be improved. 7. Modification of the invention (a) Even when there are more than two pairs of excitation coils, the same effect can be obtained by selectively connecting them according to the patterns shown in the table above. (b) Multiple pairs of electrodes may be provided. In this case,
An averaging circuit may be provided to average the output signals from each pair of electrodes. 8. Effects of the invention According to the invention, a sub-excitation coil is provided in addition to the main excitation coil, and the main excitation coil and the sub-excitation coil are connected by an excitation coil connector according to switching of the measurement span corresponding to the flow velocity of the fluid to be measured. By switching the energization in a predetermined pattern, the magnetic flux density near the electrode is increased in the low flow velocity region to increase the signal electromotive force, and even if the excitation current is reduced, sufficient electromotive force necessary for measurement can be obtained. This allows the magnetic flux waveform to rise sufficiently even if the excitation frequency is higher than that of conventional commercially available products. Furthermore, in the high flow velocity region, a functional distribution magnetic field is obtained to prevent measurement errors due to fast pulsations in the fluid and variations in flow velocity distribution. By switching the magnetic field distribution in accordance with the magnitude of the flow velocity, the disadvantage of conventional low-frequency excitation electromagnetic flowmeters, which is the problem of "magnetic We were able to improve the difficulty of measuring fluids containing rapid pulsation.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing a conventional example of a low frequency excitation electromagnetic flowmeter, Fig. 2 is a waveform diagram showing the signal electromotive force waveform of a square wave excitation electromagnetic flowmeter, and Fig. 3 is an electromagnetic flowmeter according to an embodiment of the present invention. FIG. 4 is a block diagram showing a flowmeter, and is an explanatory diagram showing a cross section perpendicular to the tube axis of a measuring tube including a pair of electrodes. 3...Measurement tube, 3a...Electrode, 3b...Insulating lining, 4...Signal electromotive force line, 5a, 5b...
... Excitation line, 7 ... Preamplifier, 9 ... Converter with synchronous sampler, 10 ... Synchronous signal generator, 11 ...
Low frequency excitation power generator, 12...Power power supply, 1
4... Output signal, 2a, 2a'... Main excitation coil,
21...Electromagnetic flowmeter detector, 21a...Outer casing, 2
2, 22'...Subexcitation coil, 25...Excitation coil connector, 26...Magnetic flow meter converter, 28...
Span setting device with span information transmitter.

Claims (1)

[Scope of utility model registration request] A measuring tube through which a fluid passes, at least one pair of electrodes arranged opposite to the measuring tube in a direction perpendicular to the tube axis of the measuring tube, and at least one pair of electrodes that are perpendicular to the straight line connecting the electrodes and the direction of fluid flow. A pair of main excitation coils, at least one pair of sub-excitation coils whose coil heads are disposed closer to the electrodes than the main excitation coils and which are perpendicular to the straight line connecting the electrodes and the direction of fluid flow; an electromagnetic flowmeter detector comprising an outer casing, a span setting device with a span information transmitter that transmits span information corresponding to a set measurement span, and a synchronization signal transmitter that transmits a synchronization signal of a predetermined frequency; a converter with a synchronous sampler that samples a signal electromotive force using a synchronous signal from the synchronous signal generator and outputs a span flow rate signal corresponding to span information from the span setting device;
A low-frequency excitation power generator generates excitation power at the frequency of the synchronization signal from the synchronization signal generator, and the excitation power from the low-frequency excitation power generator is used to generate span information from the span setting device with span information transmitter. an electromagnetic flowmeter converter comprising an excitation coil connector selectively connected to the main excitation coil and the sub-excitation coil in a pattern determined by the method.