How Does a Quadrature Flowmeter Work?

The quadrature flowmeter is based upon physical laws relating to the flow of liquids and the ability to measure the liquid flow by using a magnetic field. The device yields a linear average of a conductive liquid's flow rate.

Faraday's Law

• Electromagnetic flowmeters are based upon Faraday's Law, which states that moving a conductor through a magnetic field will induce a current. Energized coils outside the tube combine with the fluid as a conductor to carry the current.

Quadrature Flowmeters

• Quadrature flowmeters use AC current. This results in a line frequency change approximately 50 to 60 times per second. A loop of conductive wire can be located in the magnetic field to generate a voltage. The voltage will be 90 degrees out of phase with the primary magnetic field. This is often referred to as quadrature.

Minimizing Quadrature

• The electrode wires must be arranged in parallel with the lines of flux to minimize the quadrature error. The continuous alternation of the current in an AC field makes this error significant. This situation requires the use of phase-sensitive circuitry that will reject the quadrature. This leads to the problem of the circuitry rejecting the true voltage flow signal and causing an error. Therefore, the flowmeter's signal lines must be isolated to maintain signal integrity.