Electromagnetic flowmeter

• US 4,651,286 A
• Filed: 06/18/1984
• Issued: 03/17/1987
• Est. Priority Date: 06/23/1983
• Status: Expired due to Fees

• Current Assignee: Yokogawa Electric Corporation
• Original Assignee: Yokogawa Hokushin Electric Corp. (Yokogawa Electric Corporation)
• Inventors: Fukai, Yoshio, Goto, Shigeru
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Laibowitz, Danielle
• Application Number:
  US06/621,509
• Time in Patent Office: 1,002 Days
• Field of Search: 364/510, 364/571, 73/861.17, 73/861.12, 73/861.16
• US Class Current: 702/45
• CPC Class Codes: G01F 1/60 Circuits therefor

Abstract

An electromagnetic flow meter comprising an electromagnetic flow signal generator having a pipe through which a fluid to be measured flows, an exciting coil and a pair of electrodes, an exciting circuit for supplying an exciting current whose normal value is switched at a low frequency to the exciting coil of the generator, and a signal processing circuit for effecting an arithmetic operation and outputting a flow rate signal concerning the flow rate of the fluid based on voltages induced between the electrodes of the generator; wherein to keep constant the exciting current, the exciting circuit comprises a switching regulator for stabilizing a power supply voltage and producing an exciting DC voltage dependent on a voltage setting, a switching circuit connected between the exciting coil and the switching regulator and applying the exciting voltage, while turning ON and OFF at a low frequency, to the exciting coil and an exciting current detection means connected in series between the switching regulator and the exciting coil for detecting the exciting current flowing through the exciting coil, and the signal processor comprises means for taking a signal corresponding to the exciting current from the exciting current detection means, effecting an arithmetic operation relative to a predetermined reference value for determining the level of the normal value of the exciting current and supplying a voltage setting based on the result of the arithmetic operation to the switching regulator. Power consumption is thus lowered, efficiency is increased, and reduction in size of the circuit is achieved.

Claims

1. An electromagnetic flowmeter comprising

an electromagnetic flow signal generator including electrodes disposed across a fluid flow and an exciting coil positioned closely to said fluid flow;

an exciting circuit having a switching regulator for stabilizing a power supply voltage and producing a DC voltage dependent on a voltage setting, said exciting circuit being arranged to supply said exciting coil of said electromagnetic flow signal generator with an exciting current having a normal value of zero in a quiescent period and a positive or negative normal value in an exciting period, said quiescent period and said exciting period being periodically switchable; and

a signal processing circuit having a microcomputer programmed with

logic for sampling signal voltages related to voltage induced between said electrodes in said quiescent and exciting periods of said exciting current,

logic for sampling a voltage produced by detecting said exciting current flowing in said exciting period,

logic for reading the sampled voltages as digital signals;

logic for effecting an arithmetic operation on said digital signals to compute a flow rate signal, and

logic for controlling said voltage setting for said switching regulator;

wherein said voltage setting for said switching regulator is switched to a larger value in said quiescent period of said exciting current than in said exciting period.

2. An electromagnetic flowmeter comprising

an electromagnetic flow signal generator including electrodes disposed across a fluid flow and an exciting coil positioned closely to said fluid flow;

an exciting circuit having a switching regulator for stabilizing a power supply voltage and producing a DC voltage dependent on a voltage setting, said exciting circuit being arranged to supply said exciting coil of said electromagnetic flow signal generator with an exciting circuit having a normal value of zero in a quiescent period and a positive or negative normal value in an exciting period, said quiescent period and said exciting period being periodically switchable; and

a signal processing circuit having a microcomputer programmed with

logic for sampling signal voltages related to voltages induced between said electrodes in said quiescent and exciting periods of said exciting current,

logic for sampling a voltage produced by detecting said exciting current flowing in said exciting period,

logic for reading the sampled voltages as digital signals,

logic for effecting an arithmetic operation on said digital signals to compute a flow rate signal, and

logic for controlling said voltage setting for said switching regulator;

wherein said switching regulator has a first output terminal to which a positive DC voltage is applied and a second output terminal to which a negative DC voltage is applied; and

wherein said exciting circuit further comprises a first capacitor of small capacitance connected through a first reverse current blocking diode to said first output terminal, a second capacitor of small capacitance connected through a second reverse current blocking diode to said second output terminal, means connecting a series connected circuit comprising a first switch and said exciting coil parallel to said first capacitor, means connecting a series connected circuit comprising a second switch and said exciting coil parallel to said second capacitor, and diodes connected parallel, respectively, to said first and second switches, for allowing currents to flow in directions opposite to the directions in which the exciting current flows through said first and second switches.

3. An electromagnetic flow meter comprising an electromagnetic flow signal generator having a pipe through which a flow to be measured flows, an exciting coil and a pair of electrodes, an exciting circuit for supplying an exciting current whose normal value is switched at a low frequency to the exciting coil of the electromagnetic flow signal generator and a signal processing circuit for effecting an arithmetic operation and outputting a flow rate signal related to the flow rate of the fluid to be measured based on voltages induced between the electrodes of the electromagnetic flow signal generator, wherein said exciting circuit comprises

a switching regulator for stabilizing the power supply voltage and producing an exciting DC voltage corresponding to the voltage setting;

a switching circuit connected between said exciting coil and said switching regulator for supplying said exciting voltage while turning ON and OFF at a low frequency to said exciting coil; and

an exciting current detection means connected in series between said switching regulator and said exciting coil for detecting the exciting current flowing through said exciting coil; and

wherein said signal processing circuit comprises means for taking a signal corresponding to the exciting current from said exciting current detection means, effecting an arithmetic operation relative to a predetermined reference value for determining the level of the normal value of said exciting current and supplying the voltage setting based on the result of the arithmetic operation to said switching regulator;

further comprising a first capacitor of a small capacitance connected to the first output terminal for outputting the positive DC voltage of the switching regulator by way of a first reversed current blocking diode;

a second capacitor of a small capacitance connected to the second output terminal for outputting the negative DC voltage of the switching regulator by way of a second reversed current blocking diode;

a first switch of a switching circuit connected between said first capacitor and said exciting coil;

a second switch of a switching circuit connected between said second capacitor and said exciting coil; and

diodes connected respectively in parallel with said first and second switches and through which currents flow in directions opposite to those of the currents flowing through said first and second switches.

4. The flow meter of claim 3, wherein the switching regulator comprises

a serial circuit of a primary winding of a transformer and a switching element applied with a voltage from a power supply by way of a rectifying circuit and a smoothing capacitor;

means for rectifying and smoothing the secondary current produced in the first secondary winding of said transformer upon turning ON and OFF of said switching element and outputting a positive DC voltage;

means for rectifying and smoothing the secondary current produced in the second secondary winding of said transformer upon turning ON and OFF of said switching element and outputting a negative DC voltage;

means for rectifying and smoothing the secondary current produced in the third secondary winding of said transformer upon turning ON and OFF of said switching element and obtaining a DC feedback voltage; and

means for controlling the ON and OFF of said switching element so as to equalize said feedback voltage with the voltage setting.

5. The flow meter of claim 3, wherein the signal processing circuit takes a signal corresponding to the exciting current detected by the exciting current detection means, effects an arithmetic calculation relative to a predetermined reference value for determining the level of the normal value of said exciting current, outputs the result of the arithmetic operation as a pulse width signal and supplies said pulse width signal as a voltage setting to the switch regulator after converting the signal into a voltage in a pulse width voltage conversion circuit.

6. An electromagnetic flowmeter comprising an electromagnetic signal generator having a pipe through which a fluid to be measured flows, an exciting coil and a pair of electrodes, an exciting circuit for supplying an exciting current whose normal value is switched at a low frequency to the exciting coil of the electromagnetic flow signal generator and a signal processing circuit for effecting an arithmetic operation and outputting a flow rate signal related to the flow rate of the fluid to be measured based on voltages induced between the electrodes of the electromagnetic flow signal generator, wherein said exciting circuit comprises

a switching regulator for stabilizing the power supply voltage and producing an exciting DC voltage corresponding to the voltage setting;

a switching circuit connected between said exciting coil and said switching regulator for supplying said exciting voltage while turning ON and OFF at a low frequency to said exciting coil; and

an exciting current detection means connected in series between said switching regulator and said exciting coil for detecting the exciting current flowing through said exciting coil; and

wherein said signal processing circuit comprises means for taking a signal corresponding to the exciting current from said exciting current detection means, effecting an arithmetic operation relative to a predetermined reference value for determining the level of the normal value of said exciting current and supplying the voltage setting based on the result of the arithmetic operation to said switching regulator;

wherein the signal processing circuit takes a signal corresponding to the exciting current detected by the exciting current detection means, effects an arithmetic calculation relative to a predetermined reference value for determining the level of the normal value of said exciting current, outputs the result of the arithmetic operation as a pulse width signal and supplies said pulse width signal as a voltage setting to the switch regulator after converting the signal into a voltage in a pulse width voltage conversion circuit;

wherein the pulse width signal is supplied by way of insulation means to the pulse width voltage conversion circuit.

7. An electromagnetic flow meter comprising an electromagnetic flow signal generator having a pipe through which a fluid to be measured flows, an exciting coil and a pair of electrodes, an exciting circuit for supplying an exciting current whose normal value is switched at a low frequency to the exciting coil of the electromagnetic flow signal generator and a signal processing circuit for effecting an arithmetic operation and outputting a flow rate signal related to the flow rate of the fluid to be measured based on voltages induced between the electrodes of the the electromagnetic flow generator, wherein said exciting circuit comprises

a switching regulator for stabilizing the power supply voltage and producing an exciting DC voltage corresponding to the voltage setting;

a switching circuit connected between said exciting coil and said switching regulator for supplying said exciting voltage while turning ON and OFF at a low frequency to said exciting coil; and

an exciting current detection means connected in series between said switching regulator and said exciting coil for detecting the exciting current flowing through said exciting coil; and

wherein said signal processing circuit comprises means for taking a signal corresponding to the exciting current from said exciting current detection means, effecting an arithmetic operation relative to a predetermined reference value for determining the level of the normal value of said exciting current and supplying the voltage setting based on the result of the arithmetic operation to said switching regulator;

wherein the signal processing circuit monitors when the taken signal corresponding to the exciting current is within an allowable range or not and outputs an alarm signal when it is out of the allowable range and judging it as an abnormality in the exciting coil.

8. An electromagnetic flow meter comprising an electromagnetic flow signal generator having a pipe through which a fluid to be measured flows, an exciting circuit for supplying an exciting current having a normal value zero in a quiescent period and a positive or negative normal value in an exciting period, said periods being switchable at a low frequency, and a signal processing circuit having a microcomputer for effecting an arithmetic operation and outputting a flow rate signal related to a flow rate of said fluid to be measured based on voltages induced across the electrodes of said electromagnetic flow signal generator;

wherein said exciting circuit comprises

a switching regulator for stablizing the power source voltage and outputting an exciting DC voltage depending on the voltage setting;

a switching circuit connected between said exciting coil and said switching regulator and applying said exciting voltage to said exciting coil while turning ON and OFF at a low frequency; and

exciting current detection means connected in series between said switching regulator and said exciting coil for detecting the exciting current flowing through said exciting coil; and

wherein said signal processing circuit comprises means for taking a signal corresponding to the exciting current from said exciting current detection means, effecting an arithmetic operation related to a predetermined reference value for determining the level of the normal value of said exciting current and alternately supplying the voltage setting in the quiescent period and the voltage setting in the excited period to said switching regulator based on the result of the arithmetic operation;

wherein the voltage setting in the quiescent period is made greater than the voltage setting in the excited period of the switching regulator.