Intro to flow measurement and control - part 3 Non-Mechanical Flow Meters
When we first started to measure flow of liquids it was for water used in irrigation of farmlands. The need for the accuracy we have today was not as it is today. The accuracy of the earliest flow meters could be off a few gallons a day an there was no significant loss or problems as a result. Today's flow meters are accurate to small measurements that were unheard of a century ago.
As time progressed from the early flow control devices we not only needed greater accuracy but had to actually define new and smaller units of measurements. The units of measurement and accuracy of flow meters we use today are incredibly small and cannot be discerned with the naked eye. Without these small units of measurement and the new devices that use them there would not be the technological marvels we have today.
With all the increased need for accuracy new types of flow meters were created. One of the great needs was to have a flow measurement device that would not affect downstream pressure. These new flow meters work using electronics, sound and magnetisms. These new devices had their own issues such as requiring a certain temperature range to remain accurate. There is no way that we would have the level of technology we have now without the newer flow meters.
Of the non-mechanical flow meters the magnetic flow meter is the most common. A magnetic flow meter applies a magnetic field to the metering tube. The magnetic field fluctuates, as liquid flows through the metering tube and these fluctuations are proportional to the velocity of the liquid. To use a magnetic flow meter you need to be measuring flow of a liquid that is conductive such as water.
Ultrasonic flow meters can measure volumetric flow by sensing bubbles or particulates in the liquid flow. This type of flow meter is ideal for wastewater and other "dirty" liquids. No part of this type of flow meter makes actual contact with the liquid flow and therefore they will not affect the downstream pressure at all. Ultrasonic flow meters can also be used with clean liquids like water if it is possible to introduce bubbles someplace upstream of the device.
The coriolis type of flow meters measure mass flow instead of the volumetric flow. They operate by passing liquid through one or more tubes (normally shaped like a "U") that vibrates. As the fluid passes through the tubes it will reach a point of maximum vibration then it will decelarate as it leaves this point. The acceleration and deceleration will cause the tubes to twist and this twisting action can be measure and correlated to determine the mass flow through a channel or conduit.
These articles provide only a small amount of information about flow meters and is kept very basic. We hope this is helpful to you an that our basic primer will help you understand some of the more advanced information presented on sites we link to.