User:Jof307~enwiki/CoriolisWeigher

A Coriolis Weigher, Coriolis Scale, Coriolis Flow Weigher or Rotor Weigher is a scale which measures the weight of a mass flow by utilizing the Coriolis effect. Products measured by the Coriolis Weigher are bulk materials, dust (e.g.carbon dust), powder and flour, also granules and grain. The Coriolis Weigher should not be confused with a coriolis flow meter, which measures mass of liquids and gases.

Design
The Coriolis Weigher consists schematically of a feed pipe, a motor which drives a rotor plate and a discharge funnel. There are different construction types in particular concerning the feeding configuration and the rotor plate. The construction in principle is yet comparable with the one which is shown on the picture.

Function
The product to be weighed is conducted through the feed pipe into the middle of the rotor plate. The rotor plate is rotating with a fixed rotational speed. It accelerates the mass flow by means of its radial arranged wings. The mass flow escapes the rotor plate in tangential direction. It slides through the discharge funnel spirally leaving the weigher.

The torque which is required to accelerate the product circularly is measured and evaluated. It is proportional to the mass flow.

There are different method of measuring the torque.

One method is to measure the current consumed by the motor. Due to the influence of loss and perturbation this method is inaccurate.

Another method is to place the motor in a commuting bearing. The resulting force affecting the motor is measured by a strain gauge. The torque is measured directly. Friction of the bearing go into measurement as error. Thatswhy this method is qualified for mass flows of more than approx. 1 t/h.

A further method is capable of avoiding friction influence by a precise suspension and abandonment of bearings and strain gauge. Thereby it is possible to weigh mass flows far below 1 t/h precisely.

Advantages
Measurement of mass flows with the Coriolis Weigher is nearly boundless. Weighers have been realised of capacities up to 150 t/h.

An advantage of the Coriolis Weigher is the elimination of product friction. The friction appears in radial direction along of the wings. The force measurement is realised in tangential direction. Products with different properties (for example density and viskosity) can be weighed without recalibration.

A further advantage is the wide field of application. Mass flows with different attributes (e.g. granules, grain, products with cohesive attributes such as carbon dust, cellulose, flour, bran,...) can be measured.

In comparison with Baffle Plate Weighers the Coriolis Weigher has less error in measurement (approx. 0.5 %).

Advancements have turned the Coriolis Weigher to a robust measuring device that works even under vibrations and thrusts with the same accuracy.

Disadvantages
A disadvantage of the Coriolis Weigher is - compared to hopper scales - its high price.

Also the measurement of the mass flow is affected by an imprecisely assembled feeding. Thatswhy a precise feed pipe installation is essential.

The bureau of standards does not gauge Coriolis Weighers because accuracy classes in standardization are not reached. Yet for high capacities it has been done.

The Coriolis Weigher measures the amount of air which is passing through. If this air flow is constant, it can be eliminated by taring. A fluctuating air flow leads to errors in measurement.

Weblinks

 * Lessons and visualisation of Coriolis effect
 * Manufacturer of Corolis Weighers

Category:Scale