Electromagnetic flowmeter deriving power from signalling loop current

An electromagnetic flowmeter for measuring a rate of flow of a fluid at a measuring location arranged for connection in a current signalling loop, the electromagnetic flowmeter comprising:

• a coil for generating a magnetic field in said fluid at the measuring location;
• a coil current supply connected to the coil for supplying current to said coil;
• electrodes in the fluid at the measuring location for detecting a voltage generated across the flow;
• a signal processor having an input connected to the electrodes for detecting the voltage generated across the electrodes;
• power supply circuitry connected in the current signalling loop for drawing power from the current signalling loop, connected to the coil current supply to supply power thereto, and connected to the signal processor to supply current thereto;
• a current signalling loop current controller for controlling a current in the current signalling loop to a value indicative of the rate of flow of said fluid based on an output of the signal processor, the current signalling loop current controller controlling the current in the current signalling loop to a predetermined minimum value at a predetermined maximum rate of flow of said fluid and controlling the current in the current signalling loop to a predetermined maximum value at a minimum or zero rate of flow of said fluid;
• and
• a control element operatively coupled to the coil current supply and the power supply to cause the coil current supply to supply a greater current to the coil at a lower rate of flow of said fluid than at a higher rate of flow of said fluid.

An electromagnetic flowmeter for measuring a rate of flow of a fluid at a measuring location arranged for connection in a current signalling loop, the electromagnetic flowmeter comprising:

• a coil for generating a magnetic field in said fluid at the measuring location;
• a coil current supply connected to the coil for supplying coil current to said coil;
• electrodes in the fluid at the measuring location for detecting a voltage generated across the flow;
• a signal processor having an input connected to the electrodes for detecting the voltage generated across the electrodes;
• power supply circuitry connected in the current signalling loop for drawing power from the current signalling loop, connected to the coil current supply to supply power thereto, and connected to the signal processor to supply current thereto;
• and
• a current signalling loop current controller connected in the current signalling loop for controlling a current in the current signalling loop to a value indicative of the rate of flow of said fluid based on an output of the signal processor, the current signalling loop current controller controlling the current in the current signalling loop to a predetermined minimum value at a predetermined maximum rate of flow of the fluid and controlling the current in the current signalling loop to a predetermined maximum value at a minimum or zero rate of flow of said fluid.

An improved electromagnetic flowmeter for measuring a rate of flow of a fluid at a measuring location having two terminals for connection in a current signalling loop and comprising a coil for generating a magnetic field in the fluid at the measuring location;

• a coil current supply connected to said coil for supplying coil current to said coil, electrodes in the fluid at the measuring location for detecting a voltage generated across the flow;
• a signal processor connected to the electrodes for detecting the voltage generated across the electrodes, power supply circuitry connected in the current signalling loop for drawing power from the current signalling loop to power the coil current supply and the signal processor;
• and a current signalling loop current controller connected in the current signalling loop and for controlling a current in the current signalling loop to a value indicative of the rate of flow of said fluid based on an output of the signal processor, the power supply circuitry and the current signalling loop current controller being coupled between the terminals for connection in the current signalling loop, wherein the improvement comprises:
• the current signalling loop current controller is connected to the current signalling loop and to the output of the signal processor to increase the current in the current signalling loop as the rate of flow of said fluid decreases and decreases the current in the current signalling loop as the rate of flow of said fluid increases.