Electromagnetic flowmeter

• US 5,621,177 A
• Filed: 08/14/1995
• Issued: 04/15/1997
• Est. Priority Date: 03/02/1995
• Status: Expired due to Term

• Current Assignee: Yokogawa Electric Corporation
• Original Assignee: Yokogawa Electric Corporation
• Inventors: Torimaru, Takashi
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): BIEGEL, RONALD L
• Application Number:
  US08/514,877
• Time in Patent Office: 610 Days
• Field of Search: 73/861.12, 73/861.16, 73/861.17
• US Class Current: 73/861.16
• CPC Class Codes: G01F 1/60 Circuits therefor

Abstract

An electromagnetic flowmeter for converting flow rate of a fluid to be measured into an electrical signal and for outputting a flow rate signal corresponding to the flow rate using detecting electrodes, comprising exciting means for applying a magnetic field to the fluid with an excitation period thereof being shorter than the non-exciting period; AC coupling means for obtaining an AC signal through AC coupling of signals outputted from the electrodes sample and hold means for sampling and holding the AC signals with a sampling signal having a sampling width including portions before and after the excitation period, and for outputting the resulting sample and hold signal as a hold signal; switching means for changing a reference potential before and after the sample and hold; and signal processing means for processing the hold signal to produce the flow rate signal.

Claims

1. An electromagnetic flowmeter for converting flow rate of a fluid to be measured to an electric signal and for outputting a flow rate signal corresponding to said flow rate through detecting electrodes, said electromagnetic flowmeter comprising:

exciting means for intermittently causing an exciting current to flow thereby to apply a magnetic field to said fluid, an exciting period of said exciting current being shorter than a non-exciting period thereof;

AC coupling means for obtaining an AC signal through an AC coupling of inter-electrode signals outputted from said detecting electrodes;

first sample and hold means for sampling and holding said AC signal with a sampling signal having a sampling width including portions before and after said excitation period, and for outputting the resulting sampled and held signal as a first hold signal;

switching means for switching the output of said first sample and hold means to a reference potential before and after said period of sample and hold; and

signal processing means for processing said hold signal and for outputting the resulting signal as said flow rate signal.

2. The flowmeter of claim 1, wherein said detecting electrodes detect flow rate through use of capacitance.

3. The flowmeter of claim 2, wherein said switching means comprises a first switching means for switching said AC signal and said reference potential by use of a first switching signal, and second switching means for switching said hold signal and said reference potential by use of a second switching signal at a time after said sample and hold processing step.

4. The flowmeter of claim 2, wherein a waveform of said exciting current is at least partially triangular in shape.

5. The flowmeter of claim 1, wherein said detecting electrodes detect flow rate through contact with said fluid to be measured.

6. The flowmeter of claim 5, wherein said switching means comprises a first switching means for switching said AC signal and said reference potential by use of a first switching signal, and second switching means for switching said hold signal and said reference potential by use of a second switching signal at a time after said sample and hold processing step.

7. The flowmeter of claim 5, wherein a waveform of said exciting current is at least partially triangular in shape.

8. The flowmeter of claim 1, wherein said switching means comprises a first switching means for switching said AC signal and said reference potential by use of a first switching signal, and second switching means for switching said hold signal and said reference potential by use of a second switching signal at a time after said sample and hold processing step.

9. The flowmeter of claim 1, wherein a waveform of said exciting current is at least partially triangular in shape.

10. The flowmeter of claim 1, wherein a battery is used as a driving power supply for said exciting means and said signal processing means.

11. An electromagnetic flowmeter for converting a flowrate of a fluid to be measured to an electrical signal and for outputting a flow rate signal corresponding to said flow rate through detecting electrodes, said electromagnetic flowmeter comprising:

exciting means for intermittently causing an exciting current to flow thereby to apply a magnetic field to said fluid to be measure, an exciting period of said exciting current being shorter than a non-exciting period thereof;

AC coupling means for obtaining an AC signal through an AC coupling of inter-electrode signals outputted from said detecting electrodes;

first sample and hold means for sampling and holding said AC signal with a first sampling signal having a sampling width including portions before and after said excitation period , and for outputting results of said sampling and holding as a first hold signal;

switching means for switching to a reference potential before said period of sample and hold;

second sample and hold means for sampling and holding a reference voltage proportional to said exciting current with a second sampling signal and for outputting resulting sample and hold signal as a second hold signal;

voltage/frequency converter means for neutralizing said first hold signal with said second hold signal to calculate and output ratio of said first and second hold signals as a frequency signal;

counter means for counting said frequency signal; and

computer means for periodically reading results of said counting and for calculating and outputting a flow rate signal.

12. An electromagnetic flowmeter for converting flow rate of a fluid to be measured to an electric signal and for outputting a flow rate signal corresponding to said flow rate through detecting electrodes, said electromagnetic flowmeter comprising:

exciting means for intermittently causing an exciting current to flow thereby to apply a magnetic field to said fluid, an exciting period of said exciting current being shorter than a non-exciting period thereof;

AC coupling means for obtaining an AC signal through an AC coupling of inter-electrode signals outputted from said detecting electrodes;

first sample and hold means for sampling and holding said AC signal with a sampling signal having a sampling width including portions before and after said excitation period, and for ouputting the resulting sampled and held signal as a first hold signal;

switching means for switching the output of said first sample and hold means to a reference potential before and after said period of sample and hold;

signal processing means for processing said hold signal and for outputting the resulting signal as said flow rate signal;

second sample and hold means for switching from said AC signal to a reference voltage propertional to said exciting current, sampling and holding said reference voltage with said sampling signal, and for outputting the resulting sampled and held signal as a second hold signal; and

ration cancellation means for using said first and second hold signals to calculate a ratio of said reference voltage and said AC signal.

13. The flowmeter of claim 12, wherein the switching cycle of said sample switch on said reference voltage side is a fraction of the switching cycle of said sample switch on said AC signal side.

14. The flowmeter of claim 12, wherein said switching means comprises a first switching means for switching said AC signal and said reference potential by use of a first switching signal, and second switching means for switching said hold signal and said reference potential by use of a second switching signal at a time after said sample and hold processing step.

15. The flowmeter of claim 12, wherein said exciting means comprises a battery used as a driving power supply, and wherein said signal processing comprises a battery used as a driving power supply.

16. The flowmeter of claim 12, wherein a waveform of said exciting current is at least partially triangular in shape.

17. The flowmeter of claim 12, wherein said detecting electrodes detect flow rate through use of capacitance.

18. The flowmeter of claim 17, wherein the switching cycle of said sample switch on said reference voltage side is a fraction of the switching cycle of said sample switch on said AC signal side.

19. The flowmeter of claim 12, wherein said detecting electrodes detect flow rate through contact with said fluid to be measured.

20. The flowmeter of claim 19, wherein the switching cycle of said sample switch on said reference voltage side is a fraction of the switching cycle of said sample switch on said AC signal side.

21. An electromagnetic flowmeter for converting flow rate of a fluid to be measured to an electric signal and for outputting a flow rate signal corresponding to said flow rate through detecting electrodes, said electromagnetic flowmeter comprising:

exciting means for intermittently causing an exciting current to flow thereby to apply a magnetic field to said fluid, an exciting period of said exciting current being shorter than a non-exciting period thereof;

AC coupling means for obtaining an AC signal through an AC coupling of inter-electrode signals outputted from said detecting electrodes;

first sample and hold means for sampling and holding said AC signal with a sampling signal having a sampling width including portions before and after said excitation period, and for ouputting the resulting sampled and held signal as a first hold signal;

switching means for switching the output of said first sample and hold means to a reference potential before and after said period of sample and hold;

signal processing means for processing said hold signal and for outputting the resulting signal as said flow rate signal;

an analog signal processing unit disposed preceding said signal processing means; and

power supply means for supplying a voltage to only said analog signal processing unit only during a period substantially corresponding to said sampling width.

22. The flowmeter of claim 21, wherein said detecting electrodes detect flow rate through use of capacitance.

23. The flowmeter of claim 21, wherein said detecting electrodes detect flow rate through contact with said fluid to be measured.

24. The flow meter of claim 21, wherein said switching means comprises a first switching means for switching said AC signal and said reference potential by use of a first switching signal, and second switching means for switching said hold signal and said reference potential by use of a second switching signal at a time after said sample and hold processing step.

25. The flow meter of claim 21, wherein said exciting means comprises a battery used as a driving power supply, and wherein said signal processing means comprises a battery used as a driving power supply.

26. The flowmeter of claim 21, wherein a waveform of said exciting current is at least partially triangular in shape.