JPH03122523A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To enable removal of noise even when a frequency component of the noise ranges wide, by varying the frequency of an exciting current randomly. CONSTITUTION:A pipeline 1 is provided with electrodes 11 and 12. An exciting coil 2 generates a magnetic field on the basis of an output of an exciting current generating element 3 and a signal of the polarity corresponding to the direction of the magnetic field is generated between the electrodes 11 and 12. This generated signal is sampled 5 after amplification 4 and sent to an output element 6. A signal having a period T1 for supply of a current and a signal for which random pause periods T2, R3,... are made to occur alternately are sent to the generating element 3 from a timing signal generating circuit 7, the generating element 3 sends an exciting current to the coil 2 between the signals of the period T1, and magnetic fields being different in the direction of excitation are supplied alternately from the coil 2 to the pipeline 1. A random variation in the period of pause of the exciting current is synchronous with a change in a sampling pulse and thereby an excitation frequency is varied randomly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electromagnetic flowmeter that measures the flow velocity of a fluid.

[Prior Art] As is well known, there is an electromagnetic flow meter that measures the flow velocity of a fluid. This utilizes the fact that when a fluid flows through a pipe and an excitation magnetic field is applied perpendicularly to the pipe, an electrical signal corresponding to the flow velocity is obtained from the electrodes that sandwich the fluid. However, since this device handles minute electrical signals, commercial frequency noise components are likely to be superimposed on the original flow rate signal, and although the polarity of the flow rate signal is reversed when the direction of the excitation magnetic field is changed, the noise component Taking advantage of the fact that the polarity of the excitation current does not change even when the polarity of the excitation current changes, only the noise component is removed by inverting the phases of the signals before and after the polarity of the excitation current changes and adding or integrating them. This excitation current uses a rectangular wave to change the polarity, and the frequency used has been found to be 1/4 or 1/8 of the commercial frequency.

[Problem to be solved by the invention] However, for example, AgNO3, KCj, NaC
When a strong electrolyte fluid such as J flows through a pipe, noise with a value larger than that of the commercial frequency is generated over a wide range of frequencies, so in the conventional method, noise is superimposed on the excitation frequency and odd multiples of it. However, since it cannot be distinguished from the flow rate signal, there is a problem that the noise removal performance is insufficient.

[Means for Solving the Problems] In order to solve such problems, a first invention includes an excitation signal generation section that supplies an excitation signal to an excitation coil, a sampling signal generation section that samples a flow rate signal, and an excitation signal generation section that supplies an excitation signal to an excitation coil. It consists of a timing signal generation section that generates a timing signal for synchronizing the operation of the signal generation section and the sampling signal generation section, and the cycle of the timing signal generated by the timing signal generation section is made random.

In a second aspect of the invention, the flow rate signal is output through a filter, and the cutoff frequency of the filter is changed in accordance with changes in the period of the timing signal.

[Operation] Since the excitation frequency is random, noise can be removed for various frequencies, and even noise over a wide range of frequencies can be removed.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a waveform diagram showing the operation.

In the figure, 1 is a conduit made of an insulator, and 1□
and 12 are electrodes provided at positions sandwiching the fluid flowing through the conduit 1. 2 is an excitation coil and an excitation current generating section 3
A magnetic field is generated by a current supplied from the electrodes 11 and 12, and a signal having a polarity corresponding to the direction of the magnetic field is generated between the electrodes 11 and 12. Electrode 11.
The signal generated between 12 and 12 is amplified by an amplifier 4 and sampled by a sampling section 5, and the signal is outputted via an output section 6. 7 is a timing signal generation circuit that determines the timing of the sampling signal and the timing of generating an excitation current in synchronization with this timing, and the signal lines a, b, and c are connected to the signals shown in FIGS. 2(a), (b), and (c).
It is designed to generate the signal shown in the waveform diagram.

The timing signal generation circuit 7 sends a signal having a period rWIT□ and a random rest period T2.
T, , T, . . . supply signals that are generated alternately. Therefore, the exciting current generator 3 supplies the exciting current to the coil 2 while the signal of the period T1 is being supplied.
Magnetic fields with different excitation directions are alternately supplied from the coil 2 to the pipe line l. Note that the period T2 is a random period obtained by means such as a random number generator.

The timing signal generation circuit 7 supplies the timing signal shown in FIG. 2(b) to the signal line C, and the signal shown in FIG. 2(c) to the signal line C, so that the sampling section 5 samples the signal generated by the excitation current every time the excitation direction changes, as shown in FIG. 2(a).

As mentioned above, when the excitation direction is reversed, the polarity of the signal generated between the electrodes due to the interaction between the fluid and the magnetic field is also reversed, but the polarity of the noise signal generated by the chemical action between the fluid and the electrodes is not reversed. By inverting and adding the amplifier output signals at a certain sampling timing and the next sampling timing, the signal components are added, but the noise components cancel each other out, so that noise is removed. The rest period of the excitation current changes randomly, and the change is synchronized with the change in the sampling pulse. For this reason, the excitation frequency changes randomly, making it possible to distinguish between the flow rate signal and noise over a wide range of frequency bands, which is caused by the type of fluid and electrode material, and to eliminate the noise. can.

FIG. 3 shows another embodiment, in which a filter section 8 consisting of a low-pass filter is inserted between the amplifier and the sampling section, and the timing is adjusted so that the cut-off frequency of the filter has a predetermined relationship with the frequency of the excitation current. It is controlled by a signal supplied from a signal generation circuit.

Simply inserting a filter improves the noise removal performance compared to the one shown in Figure 1, but by changing the cut-off frequency of the filter in accordance with the frequency of the excitation current as shown in Figure 3, the noise removal performance is further improved. do.

[Effects of the Invention] As explained above, the present invention has the effect that noise can be removed even if the frequency components of noise range over a wide range because the frequency of the excitation current is changed randomly.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram of each part for explaining its operation, and FIG. 3 is a block diagram showing another embodiment. 1...Pipeline, 1. ．． 12... Electrode, 2...
Coil, 3... Excitation current generating section, 4... Amplifier, 5... Sampling section, 6... Output section, 7...
...Timing signal generation circuit, 8...Filter section.

Claims (2)

[Claims] (1) Generates an excitation signal generation section that supplies an excitation signal to the excitation coil, a sampling signal generation section that samples the flow rate signal, and a timing signal to operate the excitation signal generation section and the sampling signal generation section in synchronization. An electromagnetic flowmeter comprising: a timing signal generating section that generates a timing signal; the timing signal generated by the timing signal generating section has a random cycle; (2) An excitation signal generation section that supplies an excitation signal to the excitation coil; a filter that removes frequency components above a predetermined frequency in the flow rate signal; a sampling signal generation section that samples the filter output signal; and an excitation signal generation section. It consists of a timing signal generation section for operating in synchronization with the sampling signal generation section, and the timing signal generated by the timing signal generation section has a random period, and the cutoff frequency of the filter also varies depending on the period of the timing signal. An electromagnetic flow meter that is characterized by a variable flow rate.