Coriolis scales, also known as Coriolis flow rate scales or mass flow rate measuring devices, measure the weight of a mass flow using the Coriolis force.
They are most commonly used to measure bulk materials such as dusts, powder or gravel. Coriolis scales are also good for measuring granulates or cereals.
Unlike the Coriolis mass flow metering unit, Coriolis scales don’t measure liquids or gases.
The main measuring element in Coriolis scales or mass flow rate measuring devices is an impeller or measuring wheel, which is driven at constant speed. The flow of bulk material strikes this wheel axially. A deflecting cone then transports the flow radially to the guide vanes which accelerate the material to the constant circumferential speed of the measuring wheel.
The force needed to drive this acceleration is known as the Coriolis force. At constant speed, the Coriolis force can be measured using the torque required by the drive motor which is proportional to the bulk material mass flow.
The interesting thing about this system is that the physical characteristics of the bulk material, such as bulk weight, moisture and flow properties, don’t cause any errors. This is due to the Coriolis principle itself and the precise way in which torque is recorded. The drive torque needed is only produced by the accelerated mass particles. Potential friction influences on the bulk material apply vertically to the direction of measurement and therefore don’t affect the result. In order to rule out mechanical interference in the torque measurement, potential friction influences on the transfer of torque between the measuring wheel and point where torque is recorded are eliminated by an appropriate mechanical arrangement. A high-precision load cell captures the force in a matter of microseconds thanks to the evaluation electronics used.
These electronics also enable the throughput to be calculated from the load cell signal and parameters typical of the device and display this in kg/h. The total volume weighed is calculated from the throughput and displayed at the same time. An upstream feed hopper can also be adjusted to the nominal feed rate desired by the evaluation electronics.