Magnetic flowmeter with diagnostics

• US 6,014,902 A
• Filed: 11/04/1997
• Issued: 01/18/2000
• Est. Priority Date: 12/28/1995
• Status: Expired due to Term

• Current Assignee: Schneider Electric Systems USA, Inc. (Schneider Electric SE)
• Original Assignee: The Foxboro Company (Schneider Electric SE)
• Inventors: Fonteneau, Norman, Lewis, Peter B.
• Primary Examiner(s): Fuller, Benjamin R.
• Assistant Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US08/964,303
• Time in Patent Office: 805 Days
• Field of Search: 73/861.12
• US Class Current: 73/861.12
• CPC Class Codes: G01F 1/002 wherein the flow is in an open channel
• CPC Class Codes: G01F 1/60 Circuits therefor
• CPC Class Codes: G01F 25/10 of flowmeters

Abstract

A magnetic flowmeter has a tube for supporting fluid flow including a circuit for indicating when the tube is empty to prevent an erroneous flow signal from being provided by the flowmeter, as well as a diagnostic circuit indicating when electrodes in the flowmeter are partially fouled. The circuits include an amplifier connected to two electrodes in the tube and a variable resistor. In a normally operating mode, the amplifier produces an oscillating signal when the tube is empty, and in a diagnostic mode, the amplifier produces an oscillating signal when the electrodes are partially fouled.

Claims

1. A magnetic flowmeter comprising:

a tube for supporting a fluid flow;

an electrode mounted in the tube used to measure a rate of the fluid flow; and

a diagnostic circuit receiving an output of the electrode and providing an output signal which indicates when the electrode is partially fouled.

2. The flowmeter of claim 1 wherein the diagnostic circuit includes a means for repeatedly enabling the circuit.

3. The flowmeter of claim 1 wherein after the diagnostic circuit is enabled, the output signal substantially oscillates if the electrode is partially fouled.

4. A circuit for processing the output of an electrode in a fluid-supporting tube of a magnetic flowmeter comprising:

a device receiving an output of the electrode; and

a diagnostic subcircuit connected to the device, the diagnostic subcircuit causing an output signal of the device to oscillate if the electrode is partially fouled.

5. The circuit of claim 4 further comprising:

a second subcircuit connected to the device, the second subcircuit causing an output signal of the device to oscillate when the tube is empty of fluid.

6. The circuit of claim 5 further comprising a means for repeatedly enabling the diagnostic subcircuit.

7. The circuit of claim 6 wherein the diagnostic subcircuit and the second subcircuit include a digitally controlled variable resistance with a diagnostic control value and a second control value respectively, and wherein enabling the diagnostic subcircuit includes controlling the variable resistance with the diagnostic control value.

8. A method for detecting when an electrode immersed in a fluid has partially fouled, comprising:

measuring an output of the electrode normally immersed in fluid;

providing the output to a circuit;

configuring the circuit so that the circuit provides an non-oscillating output when the electrode is not fouled; and

providing an indication that the electrode has partially fouled based on an oscillating output of the circuit.

9. A method for detecting a high impedance between two electrodes normally immersed in a fluid and a fluid ground, the method comprising:

measuring an output of the two electrodes;

providing the output to a circuit;

configuring the circuit so that the circuit provides an oscillating output when a high impedance is present between the electrodes and the fluid ground;

providing an indication that the electrodes are not immersed based on the oscillating output,

periodically determining whether the electrodes have partially fouled, including configuring the circuit so that the circuit provides a non-oscillating output if the electrodes are immersed and have not fouled and provides an oscillating output if the electrodes are immersed and have partially fouled.

10. The method of claim 9 wherein configuring the circuit includes controlling a digitally controlled variable resistor.

11. A method for measuring a resistance between an electrode normally immersed in a fluid and a fluid ground, the method comprising:

providing an output of the electrode to a circuit;

configuring the circuit such that the output oscillates if the resistance is greater than a predetermined value.

12. The method of claim 11 further comprising:

sequentially configuring the circuit such that the output oscillates if the resistance is greater than a corresponding sequence of values; and

determining that the resistance is bounded by two of the sequence of values.