JPH05223607A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To achieve a highly accurate measurement of a flow rate signal by enabling the fetching of a flow rate signal component cancelling a zero point noise in a stage of measuring a flow rate. CONSTITUTION:A plurality of electromagnetic induction detection wires A1 and A2 are led out of one of a pair of electrodes counterposed on a measuring tube so as to form a reversible current loop, a signal fetching lead B is led out of the other electrode and moreover, a fluid earth wire G is led out. Signals are introduced to a flow rate conversion means 20a from specified signal lines A1, A2, B and G among these signal lines to perform a measurement of a flow rate containing a zero point noise. Signals are introduced to a zero-point noise signal conversion means 21a from the signal lines A1, A2 and B to measure a zero-point noise. Thus. a measured value of the zero-point noise obtained is introduced to a zero-point noise compensation means 22 to cancel the zero- point noise from the measured value of the flow rate containing the zero-point noise thereby fetching a flow rate signal component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flow meter using a SW (square wave) excitation method, and in particular, is provided with a technique for compensating for zero (0) point noise generated when a square wave excitation frequency is increased. Electromagnetic flowmeter.

[0002]

2. Description of the Related Art In early electromagnetic flowmeters, commercial frequency (A
The AC excitation method by C50 / 60 Hz) was used. However, in the electromagnetic flowmeter using this AC excitation method, the magnetic flux density is composed of virtual lines connecting the electrodes (virtual lines using the fluid as a conductor) and signal extraction lead wires derived from each electrode. Not only does it generate a 90 ° noise with a phase of dB / dt by interlocking with the turn coil and acting like a transformer, but also the metal such as the metallic measuring tube and the core is exposed to the magnetic flux having the phase of the magnetic flux density. And an eddy current flows in the metal to generate a secondary magnetic flux with a phase of dB / dt,
When this secondary magnetic flux interlinks with the one-turn coil, in-phase noise of opposite phase to signal phase dB ² / Dt ² = -Aω ² Asin ωt

Occurs, which causes the zero point variation. Then, due to the noise related to these alternating current phenomena, it is impossible to measure in the case of an instruction change caused by induction inside and outside the circuit, for example, in the case of a fluctuating indication or a remarkable fluctuating due to non-uniformity of electric conduction in the fluid, and a flickering instruction due to air bubbles in the fluid. Or, in the case of remarkable fluctuation, it appears that measurement is impossible, influence of noise jumping into the signal line, zero point, span drift instability, etc.

Therefore, in the AC flow type electromagnetic flowmeter,
Fluids that cannot be measured or fluids that are difficult to measure are sorted at the time of specification selection based on past experience, and such fluids are not measured, or even when such fluids are measured, they are used as a standard measurement while being used.

Therefore, in recent years, in order to improve the above problems, a low frequency SW excitation method has been used instead of the AC excitation method. This SW excitation method can be expressed by B = k in the measurement region when the magnetic flux completely rises as shown in FIGS. 7 (a) and 7 (b), so that dB / dt = dk / dt = 0 dB ² / Dt ² = 0, and no output due to a transformer-like action is generated in the one-turn coil including the electrodes.

Therefore, in the case of the electromagnetic flowmeter using the SW excitation method, various problems caused by the alternating current phenomenon can be solved, and the flow rates of various fluids which have been considered as unmeasurable fluids and difficult-to-measure fluids in the past can be obtained. It has become possible to measure.

[0007]

However, this S
Since the W excitation method has a low excitation frequency, "fluid containing solid matter (eg, earth and sand, wood chips, high concentration mortar, etc.)", "fluid with ion unevenness", "activation and sharpening of electrode surface are repeated When such a fluid is flowed, so-called 1 / f (f is frequency) noise is generated, which exhibits a frequency distribution such that its output level becomes higher as the noise frequency becomes lower. Moreover, this 1 / f noise is generated regardless of the type of excitation and the presence or absence of excitation, and there is a problem that it is difficult to separate it from the flow rate signal component.

Therefore, conventionally, noise has been removed using a noise suppressor circuit (noise removal circuit) as a means for measuring the flow rate signal component without being affected by the 1 / f noise as described above. However, when the noise level is extremely high, it is difficult to remove the noise.

Therefore, increasing the excitation frequency is most effective as an essential solution to noise elimination, and therefore, increasing the frequency as much as possible is used depending on the type of the target fluid.

However, in this case, the following problems occur. That is, when the excitation frequency is increased, in extreme terms, B = k does not hold as shown in FIG. 8, and a secondary magnetic flux having a phase of dB / dt is generated. As a result, the zero-point noise generated by the electromagnetic induction due to the rising of the magnetic flux is sampled as the square wave excitation frequency increases. The zero-point noise measurement value fluctuates due to changes in the induction-causing area s, as shown in FIG. 9, depending on dirt on the electrode surface, temperature distortion of the magnetic field generator, and the like. In general,
Zero point noise measurement value E is E = Kn · B · s · T · 10 ⁻⁸ volt

It is represented by However, Kn is a constant, B is the magnetic flux density, and T is the one-turn coil shown in FIG. In the figure, 1a and 1b are electrodes, 2 is an equivalent current line in the fluid, 3
Reference numerals a and 3b are signal extraction lead wires, and 4 is an equivalent circuit of a signal converter. That is, as is clear from the equivalent circuit of FIG. 10, the area s is usually small as shown in FIG.
When the electrode surface becomes dirty, the area s is changed as shown in FIG.
And the zero point noise measurement value E increases from the above equation.

The present invention has been made in view of the above circumstances, and provides an electromagnetic flowmeter capable of reliably erasing a zero-point noise measurement value in an actual flow rate measuring step of a target fluid and measuring a flow rate signal component with high accuracy. The purpose is to do.

[0013]

In order to solve the above-mentioned problems, the invention corresponding to claim 1 provides an electromagnetic flowmeter for performing square-wave excitation using a high excitation frequency, in which a forward and reverse current loop is formed from one electrode. A plurality of lines of electromagnetic induction detection lines to be taken out as they are formed, a signal take-out means to take out the other electrode and a signal line take-out means to take out the ground wire and a signal line taking-out means are provided to selectively and selectively output signals. A signal measuring unit that simultaneously performs flow rate measurement and zero point noise measurement by capturing, and a zero point that erases the zero point noise measurement value from the flow rate measurement value by using the zero point noise measurement value obtained by this signal measuring unit Zero point noise generated by electromagnetic induction due to insufficient rising of magnetic flux generated by square wave excitation with high excitation frequency, including noise compensation means It is configured to compensation.

Next, in the invention corresponding to claim 2, in addition to the signal line extracting means and the zero point noise compensating means which are substantially the same as those in the invention corresponding to claim 1, each signal line constituting the signal line extracting means. Among them, a predetermined signal line is selected in a fixed cycle or at an arbitrary time, zero point noise measuring means for measuring and holding zero point noise, and among the respective signal lines constituting the signal line extracting means, a predetermined signal line is selected. This is a configuration in which a signal line is selected and flow rate measuring means for measuring the zero point noise and measuring the flow rate in a time sharing manner are provided.

[0015]

Therefore, according to the invention corresponding to claim 1, by taking the above-mentioned means, signals from a plurality of electromagnetic induction detection lines forming a forward and reverse current loop centering on the signal extraction lead wire are provided. Zero point noise is measured by taking out and performing cancellation processing, on the other hand, zero point noise is included by using a signal line commonly connected to a plurality of electromagnetic induction detection lines centered on the ground line and the signal extraction lead wire. After measuring the flow rate signal, the zero point noise is deleted from the flow rate signal measurement value by using the zero point noise measurement value, so that the flow rate signal component with high accuracy can be measured in the flow rate measurement stage.

In the invention according to claim 2, the zero-point noise and the flow rate are measured in a time sharing manner, and the zero-point noise measurement value is held, while the held zero-point noise is held. Since the measurement value is used to eliminate the zero-point noise included in the flow rate measurement value, a highly accurate flow rate signal component can be measured at the flow rate measuring stage, as in the invention according to claim 1.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are views showing an embodiment of an electromagnetic flowmeter according to the present invention. 1 is a configuration diagram of a signal conversion system, FIG. 2 is a cross-sectional view of an electromagnetic flowmeter main body, FIG. 3 is an explanatory diagram of a measurement tube portion shown by cutting out a part thereof, and FIG. 4 is a diagram schematically showing FIG. Is.

As shown in FIG. 2, the main body of the electromagnetic flow meter is located on a line that divides the measuring tube 11 into two parts, and a pair of electrodes 12a and 12b are installed on the inner wall of the measuring tube so as to face each other in a liquid contact state. On the outside of 11, a pair of saddle-shaped excitation coils 13 and 13 that form a magnetic field in the direction orthogonal to the line connecting the pair of electrodes 12a and 12b and the fluid flow direction in the measurement tube.
Is provided. 14 is an outer casing.

Flow rate signal extraction from the pair of electrodes 12a and 12b is configured as shown in FIGS. That is, signal extraction lead wires (electromagnetic induction detection wires) A ₁ and A ₂ are arranged so as to form a forward / reverse current loop from one electrode, for example, the A electrode which is 12a, and taken out to the outside of the measuring tube. The signal take-out lead wire B is taken out of the measuring tube from, for example, the B electrode which is the electrode 12b.

On the other hand, the signal conversion system is divided into a flow rate measurement system 20 and a zero-point noise measurement system 21 as shown in FIG. 1, of which the flow rate measurement system 20 has a resistance (1/2) R.
(R = fluid resistance between electrodes), a common connection line for _two signal lead wires A ₁ and A ₂ , a signal lead wire B from the B electrode, the measuring tube 11 or a fluid ground wire G
To the flow rate conversion means 20a, and after taking in the signal voltages (1/2) E _sn and (1/2) E _sn here,
Signal processing of (1/2) E _sn + (1/2) E _sn = E _sn is performed to extract the flow rate signal voltage E _{sn including the} zero point noise measurement value.

Next, in the zero-point noise measuring system 21, a common connection line of _two signal lead-out leads A ₁ and A ₂ having the same resistance (1/2) R, a signal lead-out lead A ₂ and a B electrode. The lead wire B for taking out the signal from is led to the zero point noise signal converting means 21a respectively, and after taking in the signal voltages (1/2) E _sn and (1/2) E _sn here,

The signal processing of (1/2) E _sn + (1/2) E _sn + (1/2) E _sn + (− 1/2) E _sn = E _n is performed and the zero point noise measurement value E is obtained. _Take out _n . FIG. 5 is a diagram schematically showing the measurement state of the zero point noise measurement value E _n . E _n is a signal adjusted to have a magnitude corresponding to the E _n component contained in E _sn within 21 a.

Furthermore, the output E _sn of each flow rate conversion means 20a
The output E _n of the zero point noise signal converting means 21a is introduced into the zero point noise compensation means 22 for subtracting from, where (E _sn -E _n) comprising calculating a go zero point noise measurement value E
After taking out a signal that depends only on the original fluid flow rate with _n removed, the output circuit 23 outputs a flow rate signal proportional to the fluid flow rate.

Therefore, according to the configuration of the above embodiment, even when the flow rate is measured with the excitation frequency raised in the electromagnetic flow meter using the SW excitation method, the flow rate measurement is performed simultaneously with the flow rate measurement. Perform zero point noise measurement,
Since the flow rate measurement value is compensated by the zero point noise compensating means 22 using the zero point noise measurement value, even if the zero point noise occurs due to electromagnetic induction due to insufficient rising of the magnetic flux, the zero point noise is generated. Can be eliminated and only the flow rate signal component can be taken out, whereby the excitation frequency can be increased to measure the flow rate, and the flow rates of various target fluids can be measured with high accuracy.

Next, FIG. 6 is a block diagram showing another embodiment of the signal conversion system. This signal conversion system is configured to share the flow rate measurement system 20 and the zero point measurement system 21 shown in FIG. 1, and specifically, a clock signal generation source 31 for generating a clock signal at a predetermined cycle. , A predetermined signal line A ₂ − depending on the clock signal from the clock signal generation source 31.
A signal line selecting means 32 for alternately selecting B and BG, and a signal for extracting the flow rate measurement value and the zero point noise measurement value by performing the same arithmetic processing as described above for each selection signal line by the signal line selection means 32. The conversion unit 33, the hold circuit 34 that holds only the zero point noise measurement value obtained by the signal conversion unit 33, and the zero point noise measurement value held in the hold circuit 34 is subtracted from the flow rate measurement value at the time of this flow rate measurement. Thus, the zero point noise compensating means 35 for compensating the zero point noise measurement value, the output circuit 36 and the like are configured.

Therefore, according to the configuration of this embodiment, since the flow rate measurement state and the zero point noise measurement state are alternately selected, the zero point noise measurement value and the flow rate measurement value are time-shared by using the same configuration. Since the zero point noise measurement value is held and the zero point noise measurement value is used to compensate the flow rate measurement value, the rise of the magnetic flux is insufficient when sampling the measurement area, as described above. Even if zero-point noise occurs due to the resulting electromagnetic induction, the zero-point noise can be eliminated and only the flow rate signal component can be measured.

In the above embodiment, it is assumed that the flow rate measurement state and the zero point measurement state are alternately created in a predetermined cycle, but the measurement frequency of the zero point noise measurement state depends on the type of the target fluid. Can be set arbitrarily, for example, once / several seconds
It may be set once / several days. Other,
The present invention can be variously modified and implemented without departing from the scope of the invention.

[0029]

As described above, according to the present invention, the flow rate is eliminated while the zero frequency noise is eliminated in the flow rate measuring step without increasing the excitation frequency and without being restricted by the type of the target fluid. You can extract only the signal component,
As a result, it is possible to provide an electromagnetic flow meter that can measure a flow signal with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a signal conversion system in an electromagnetic flow meter according to the present invention.

FIG. 2 is a cross-sectional view of an electromagnetic flow meter body.

FIG. 3 is an explanatory view of a measurement tube portion shown by cutting out a part thereof.

FIG. 4 is a diagram schematically showing FIG.

FIG. 5 is a diagram schematically showing a configuration in a zero point noise measurement state.

FIG. 6 is a configuration diagram showing another embodiment of the signal conversion system in the electromagnetic flow meter according to the present invention.

FIG. 7 is a diagram illustrating a SW excitation method when a low excitation frequency is used.

FIG. 8 is a diagram illustrating a SW excitation method when a high excitation frequency is used.

FIG. 9 is a diagram for explaining the reason why zero-point noise occurs.

FIG. 10 is a diagram illustrating an example in which zero-point noise is generated due to surface contamination of electrodes.

[Explanation of symbols]

A ₁ , A ₂ ... Electromagnetic induction detection wire (lead wire for signal extraction),
B ... Signal extraction lead wire, G ... Ground wire, 20 ... Flow rate measuring system, 20a ... Flow rate converting means, 21 ... Zero point noise measuring system, 21a ... Zero point noise signal converting means, 22, 35 ...
Zero point noise compensation means, 23, 36 ... Output circuit, 31 ...
Clock signal generation source, 32 ... Signal line selection means, 33 ... Signal conversion means, 34 ... Hold circuit.

Claims (2)

[Claims] 1. In an electromagnetic flowmeter for performing square wave excitation using a high excitation frequency, a plurality of lines of electromagnetic induction detection lines taken out to form a forward and reverse current loop from one electrode, and a signal extraction lead taken out from the other electrode. A signal line extracting means for extracting the line and the ground wire; and a signal measuring means for simultaneously performing flow rate measurement and zero point noise measurement by selectively and selectively capturing signals from the respective signal lines forming the signal line extracting means, A zero point noise compensating means for erasing the zero point noise measurement value from the flow rate measurement value using the zero point noise measurement value obtained by the signal measuring means, and insufficient rising of the magnetic flux generated by square wave excitation at a high excitation frequency. An electromagnetic flowmeter characterized by compensating for zero-point noise generated by electromagnetic induction caused by. 2. In an electromagnetic flowmeter for performing square wave excitation using a high excitation frequency, a plurality of lines of electromagnetic induction detection lines taken out to form a forward and reverse current loop from one electrode, and a signal extraction lead taken out from the other electrode. A signal line extracting means for extracting the line and the ground line, and a predetermined signal line of the signal lines forming the signal line extracting means is selected at a constant period or at an arbitrary time, and zero point noise is measured and held. Zero point noise measuring means, and a flow rate measuring means for performing flow rate measurement in time sharing with the measurement of the zero point noise by selecting a predetermined signal line among the signal lines constituting the signal line extracting means, Zero point noise compensating means for erasing the zero point noise measurement value from the flow rate measurement value using the zero point noise measurement value measured by the zero point noise measurement means. For example, an electromagnetic flowmeter, characterized in that to compensate the zero point noise generated by electromagnetic induction caused by the rising shortage of the magnetic flux generated by the square wave excitation of the higher excitation frequency.