Method and apparatus for measuring a fluid characteristic

A densimeter comprising:

• a tube through which contains fluid;
• a piezoelectric driver mounted on the exterior of the tube;
• a piezoelectric sensor mounted on the exterior of the tube;
• a feedback loop from the sensor to the driver adapted to cause vibrations in the tube at its resonant frequency or a harmonic thereof;
• one or more strain gauges mounted on the exterior wall of the tube to sense strain exerted on the exterior wall by the pressure of fluid flowing through the tube;
• and
• a microprocessor for determining the density of the fluid contained by the tube responsive to the piezoelectric sensor and the one or more strain gauges.

A method for determining the density of a fluid flowing through a fluid system, the method comprising the steps of:

• installing a straight tube in the fluid system so fluid flowing through the system also flows through the tube;
• setting up vibrations in the tube;
• sensing the frequency of the vibrations;
• sensing strain in the wall of the tube caused by the pressure of the fluid flowing through the tube;
• and
• calculating the density of the fluid flowing through the tube from the sensed frequency and the sensed strain based on calibration constants.