JPS5811010B2 - Electromagnetic flowmeter using fluid noise - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic flowmeter that uses fluid noise, and more particularly to an electromagnetic flowmeter that incorporates the concept of a spatial filter for detecting electromotive force induced by fluid noise.

An example of an electromagnetic flowmeter that utilizes fluid noise is a correlation type electromagnetic flowmeter shown in FIG.

According to FIG. 1, a magnetic field by magnets 21 and 22 is applied in the y direction that is perpendicular to the tube axis direction z of the pipe line 1, and a pair of electrodes 31 that face each other in the x direction that is perpendicular to the z and 1 directions are applied.゜31
'(31' is not shown) and 32.32'(32' is not shown) are arranged at a distance d in the z direction, and among the signals due to fluid noise obtained between these pair of electrodes, AC Only the components are amplified by amplifiers 51 and 52, and the amplified signals are given to a correlator 6 to calculate the cross-correlation Φxy and obtain the delay time (flow rate) that gives its peak.

The above-mentioned conventional device is in practical use as an online calibration means for electromagnetic flowmeters, which are currently widely used in industrial applications. It is complicated and has several problems, such as the presence of statistical errors due to the finite correlation calculation time.

The present invention has been made in consideration of the above background,
The purpose is to provide an electromagnetic flowmeter that obtains a highly accurate flow rate signal with a simple configuration.

A detailed explanation will be given below with reference to the drawings.

FIG. 3 is an explanatory diagram of the configuration of an electromagnetic flowmeter according to an embodiment of the present invention.

In FIG. 3, the opposite direction of the pair of electrodes provided in the conduit 1 is in the x direction as in FIG. Individually arranged.

In the figure, electrodes 31 and 31' (these form a pair) are shown.

The same applies hereinafter), 32, 32' to 3636' (the electrodes of the dash code material are not shown).

The electromotive force obtained between the electrodes is processed by a signal calculation/processing means having the following configuration to obtain a flow rate signal.

7 is a signal adder, which connects electrodes 31, 31', 32, 32' to
Only the alternating current components of the electromotive force from 36 and 36' are added.

8 is a tracking bandpass filter, 9 is a waveform shaping circuit, and 10 is a frequency-voltage conversion circuit.

Center frequency fo of tracking bandpass filter 8
1 is controlled by an external control signal (analog signal), and as the control signal, the flow rate signal fo (frequency signal of this device) obtained by waveform shaping the output signal fo' of the signal adder 7 is used. (output signal) converted by the frequency-voltage conversion circuit 10 is given.

The operation in the above configuration will be explained below.

Now, as the conductive fluid to be measured flows through the conduit 1, an electromotive force proportional to the flow velocity v and the magnetic flux density B of the fluid to be measured is obtained between the pair of electrodes. It also includes the influence of fluid noise (such as small overflow and minute fluctuations, which also flow at a flow velocity v) contained in the measured fluid.

Fluid noise is a type of high-frequency limited white noise.

(See Fig. 5, Fig. 5 is a frequency spectrum diagram of fluid noise).

Therefore, the target electromotive force is only the alternating current component caused by fluid noise.

However, since the pair of electrodes 31, 31' to 36, 36' are arranged at equal intervals d in two directions, the addition of the alternating current components of the electromotive force can be said to be a signal obtained through a spatial filter. .

That is, the signal fo' is N/dv (N: 0°1.2...
It is possible to obtain a signal in which only the frequency components corresponding to (...) are selected.

Moreover, since the signal frequency obtained from between each electrode is attenuated in the high frequency region, the signal can be obtained from the adder 7.

Therefore, the flow velocity v (flow rate) can be known by measuring the frequency fo1.

In the embodiment of FIG. 3, the output fo' of the signal adder 7 is
A tracking bandpass filter 8 with a center frequency fo1 removes non-signal components, and the signal is output as a signal fo (frequency fo1) via a waveform shaping circuit 9.

The tracking bandpass filter 8 has a center frequency f
Since o1 is made to follow the signal eo corresponding to the signal fo, the function of the bandpass filter can always be maintained even if the flow velocity changes.

In the above embodiment, the signal processing of the electromotive force between each electrode is as follows:
Although the signal adder 7 that adds only AC components is included, the present invention is not limited to this.

The signal adder 7 may be replaced with a signal adder/subtracter.

The signal adder/subtractor is equipped with a plurality of + input terminals and one input terminal, and individually adds the signal applied to the + input terminal and the signal applied to the one input terminal, and also subtracts the two added signals. It is only necessary to have a function of sending out a subtraction signal.

Then, the connection with each electrode is such that the electromotive force obtained from the odd numbered electrodes is given to the + input terminal, and the electromotive force obtained from the even numbered electrodes is given to the one input terminal. Good (or vice versa).

By doing so, only the frequency components corresponding to the signal adders/subtracters are selected.

Moreover, since the signal frequency obtained from between each electrode is attenuated in the high frequency region, the signal foo=v/2d of N=0 can be obtained from the signal adder/subtractor in the most emphasized form.

Therefore, if the center frequency of the tracking bandpass filter 8 is foo = v/2d, if the signal corresponding to the signal fo is used to track the signal fo, it will be proportional to the flow velocity v (flow rate) as in the above embodiment. It is possible to obtain a frequency signal that

In the above embodiments, the magnetic field is illustrated as a DC magnetic field, but the present invention does not need to be limited to this.

As described in detail above, the electromagnetic flowmeter according to the present invention detects the electromotive force induced by fluid noise contained in the fluid to be measured through the electrodes that constitute the spatial filter, and Since the components are selected to form the flow rate signal, the following features can be mentioned.

(■) Since the flow rate signal is obtained as a frequency signal,
It is easy to obtain a reading and display means with a simple structure and high accuracy.

(■) Even when using a DC magnetic field, the influence of electrochemical noise near the electrode can be ignored (the time constant of electrochemical noise is large).

) (■) The zero point of the flow signal is essentially stable.

(■) The influence of changes in magnetic field strength does not appear on the flow rate signal.

(■) If the electrode installation spacing d is known accurately, an electromagnetic flowmeter can be calibrated simply by configuring the electrical circuit without passing the actual flow rate through the pipe.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the configuration of a conventional correlation type electromagnetic flowmeter;
FIG. 3 is an explanatory diagram of a correlation function, FIG. 3 is an explanatory diagram of the configuration of an electromagnetic flowmeter according to an embodiment of the present invention, and FIG. 4 is a frequency spectrum diagram of fluid noise. 1... Pipe line, 21, 22... Magnet, 31-36...
・Electrode, 7... Signal adder, 8... Tracking,
Bandpass filter, 9... Waveform shaping circuit, 10...
・Frequency voltage converter.

Claims (1)

[Scope of Claims] 1 A magnetic field is applied in the y direction perpendicular to the pipe axis direction 2 of the pipe through which the fluid to be measured flows, and the magnetic field is generated between a pair of electrodes arranged in the x direction perpendicular to both the z and 1 directions. An electromagnetic flowmeter that determines the flow rate of a fluid to be measured from electric power, comprising a plurality of the electrodes arranged at equal intervals d in the z direction, and a circuit that adds only the alternating current component of the electromotive force of each electrode. An electromagnetic flowmeter using fluid noise, characterized in that the flow rate of the fluid to be measured is determined from the wave number component signal from the adding circuit. 2 Apply a magnetic field in the y direction, which is perpendicular to the axial direction z of the tube through which the fluid to be measured flows, and determine the flow rate of the fluid to be measured from the electromotive force between a pair of electrodes arranged in the x direction, which is perpendicular to both z and 1. In an electromagnetic flowmeter, a plurality of electrodes are arranged at equal intervals d in two directions, and serial numbers (1, 2, 3...・・）
Based on this, a signal adder/subtractor is provided which collectively adds the electromotive force groups obtained from the odd numbered electrodes, collectively adds the electromotive force groups obtained from the even numbered electrodes, and subtracts both added signals.
．． An electromagnetic flowmeter using fluid noise, characterized in that the flow rate of a fluid to be measured is determined from signals of frequency components (1, 2, . . . ).