Abstract: A tube through which fluid flows is installed in a fluid system. A piezoelectric driver is mounted on the exterior of the tube. A piezoelectric sensor is also mounted on the exterior of the tube. A feedback loop from the sensor to the driver is 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 sense the strain exerted on the exterior wall by the pressure of the fluid flowing through the tube. A. temperature sensor mounted on the exterior wall of the tube senses temperature. A microprocessor determines the density of the fluid flowing through the tube responsive to the piezoelectric sensor, temperature sensor and the one or more strain gauges. The one or more strain gauges comprise a bridge circuit. Strain gauges comprise two arms of the bridge circuit and temperature dependent resistors comprise the other two arms of the bridge.