Magnetic flow meter

A domestic water meter comprising:

• a conduit operable to guide water along a flow path;
• a magnetic field generator operable to generate an alternating magnetic field at a drive frequency across the flow path;
• a flow sensor operable to sense electromagnetic fields generated across the flow path and to output a corresponding flow sensor signal including:
• (a) an electric field component at the drive frequency and at a first phase, which electric field component varies with an electric field generated by the interaction of the magnetic field generated by said magnetic field generator and the water flowing along said flow path;
• and (b) an interfering component at the drive frequency and at a second different phase;
• a magnetic field sensor operable to sense the magnetic field generated by said magnetic field generator and to output a corresponding magnetic field sensor signal at said drive frequency at a phase related to said second phase;
• a calibration processor operable to process said magnetic field sensor signal to generate an alternating calibration control signal at said drive frequency whose phase depends upon the phase of said magnetic field sensor signal;
• a first processing circuit responsive to the calibration control signal and operable to process the flow sensor:signal to determine a measure of the strength of the electric field component thereof;
• a second processing circuit operable to process the magnetic field sensor signal to determine a measure of the strength of the magnetic field sensor signal;
• and
• a measurement processor operable to determine a measure of the flow of water in said conduit in dependence upon the determined measure of strength of said electric field component and the determined measure of strength of said magnetic field sensor signal.

A process flow control meter comprising:

• a conduit operable to guide a flow along a flow path;
• a magnetic field generator operable to generate an alternating magnetic field at a drive frequency across the flow path;
• a flow sensor operable to sense electromagnetic fields generated across the flow path and to output a corresponding flow sensor signal including:
• (a) an electric field component at the drive frequency and at a first phase, which electric field component varies with an electric field generated by the interaction of the magnetic field generated by said magnetic field generator and said flow;
• and (b) an interfering component at the drive frequency and at a second different phase;
• a magnetic field sensor operable to sense the magnetic field generated by said magnetic field generator and to output a corresponding magnetic field sensor signal at said drive frequency at a phase related to said second phase;
• a calibration processor operable to process said magnetic field sensor signal to generate an alternating calibration control signal at said drive frequency whose phase depends upon the phase of said magnetic field sensor signal;
• a first processing circuit responsive to the calibration control signal and operable to process the flow sensor signal to determine a measure of the strength of the electric field component thereof;
• a second processing circuit operable to process the magnetic field sensor signal to determine a measure of the strength of the magnetic field sensor signal;
• and
• a measurement processor-operable to-determine a measure of the flow in said conduit in dependence upon the determined measure of strength of said electric field component and the determined measure of strength of said magnetic field sensor signal.

A method of measuring a flow rate of a fluid comprising:

• providing a conduit operable to guide the fluid along a flow path;
• generating an alternating magnetic field at a drive frequency across the flow path;
• a first sensing step of sensing electromagnetic fields generated across the flow path and outputting a corresponding flow sensor signal including:
• (a) an electric field component at the drive frequency and at a first phase, which electric field component varies with an electric field generated by the interaction of the generated magnetic field and said flow;
• and (b) an interfering component at the drive frequency and at a second different phase;
• a second sensing step of sensing the magnetic field generated in said magnetic field generating step and outputting a corresponding magnetic field sensor signal at said drive frequency at a phase related to said second phase;
• using a calibration processor to process said magnetic field sensor signal to generate an alternating calibration control signal at said drive frequency whose phase depends upon the phase of said magnetic field sensor signal;
• using a first processing circuit responsive to the calibration control signal, to process the flow sensor signal to determine a measure of the strength of the electric field component thereof;
• using a second processing circuit to process the magnetic field sensor signal to determine a measure of the strength of the magnetic field sensor signal;
• and
• determining a measure of the flow in said conduit in dependence upon the determined measure of strength of said electric field component and the determined measure of strength of said magnetic field sensor signal.

A magnetic flow meter comprising:

• a conduit operable to guide a flow along a flow path;
• a magnetic field generator operable to generate a magnetic field across the flow path;
• an electric field sensor operable to sense an electric field generated across the flow path by the interaction of the magnetic field generated by said magnetic field generator and the flow in said flow path and to output a corresponding electric field sensor signal;
• a magnetic field sensor operable to sense the magnetic field generated by said magnetic field generator and to output a corresponding magnetic field sensor signal;
• a first processing circuit operable to process the electric field sensor signal to determine a measure of the strength of the electric field sensor signal;
• a second processing circuit operable to process the magnetic field sensor signal to determine a measure of the strength of the magnetic field sensor signal;
• and
• a measurement processor operable to determine a measure of the flow in said conduit in dependence upon the determined measure of strength of said electric field sensor signal and the determined measure of strength of said magnetic field sensor signal;
• wherein said magnetic flow meter has a periodic measurement cycle, wherein said first and second processing circuits are operable to process the respective sensor signals continuously during each measurement cycle and to accumulate the respective sensor signal strengths in the measurement cycle and wherein said measurement processor is operable to determine a measure of the flow along said flow path at the end of each measurement cycle using the strength measures accumulated during that cycle.