1. Field of the Invention
This invention relates to a flow meter. It has particular application to a flow meter that can measure volume flow of liquid in a pipe where that flow is turbulent and where the flow does not always fill the pipe. It has particular, but not exclusive, application to measuring volume flow of milk in a milking installation.
Flow of milk the pipes of a milking parlour is notoriously difficult to measure. The flow is turbulent, rapidly varying in direction, speed and volume, and the liquid that flows in the pipe is accompanied by a large amount of air, such that the milk fills a rapidly varying fraction of the cross-section of the pipe.
2. Summary of the Prior Art
Conventionally, the volume flow of milk in such a situation has been measured by volumetric means. Most generally, the milk is captured in a container of known volume that is repeatedly filled. The total volume flow can be determined by multiplying the number of times that the container by its volume. An example of such a system is disclosed in EP-A-0081049. Such systems can be reasonably accurate, but necessarily have a large number of moving parts. This makes them bulky, complex and expensive to manufacture. Moreover, the moving parts are difficult to clean which can lead to a build-up of contaminants. One solution to this problem is to measure electrical properties, such as conductivity, of the milk. However, such systems are of questionable accuracy, and even slight electrical leakage can cause irritation to an animal being milked. Moreover, installation of known sensors within an existing milking installation typically causes significant change to the pattern of milk flow within the installation, possibly interfering with operation of the system.
A principal aim of this invention is to provide a flow meter that is suitable for use with milk or other turbulently flowing liquids, that requires low maintenance and does not interfere with other processes, such as milking.