Flow meters are instruments used to measure the rate or volume of a moving fluid (liquid) in an open or closed conduit. They are critical components in many commercial and industrial processes, including manufacturing, fuel usage, cooling equipment, and municipal water and sewer services. There are different flow measurement technologies available, each with its own advantages and disadvantages. It's important to understand the needs of your application to select the proper flow meter.
Flow measurement can be described in two ways: volumetric flow and mass flow. Volumetric flow measures the volume of fluid passing through a flow meter, while mass flow measures the mass flow rate of the fluid passing through a flow meter. Positive displacement flow meters directly measure the volume of fluid, while other types measure the velocity of the flowing stream to determine the volumetric flow. Coriolis mass and thermal flow meters measure mass flow.
Differential pressure and variable area flow meters do not measure volume, velocity, or mass directly but instead infer its value from other measured parameters.
There are several types of flow meters are availalbe:
- Electromagnetic flow meters are volumetric flow meters that measure the voltage created when conductive liquids move through a magnetic field.
- Positive displacement flow meters measure the volumetric flow rate of a moving fluid or gas by way of precision-fitted gears or rotors containing cavities through which precisely known volumes of fluid pass.
- Rotameters or variable area flow meters consist of a uniformly tapered flow tube, a float, and a measurement scale.
- Thermal flow meters measure mass flow rate by means of measuring the heat conducted from a heated surface to the flowing fluid.
- Turbine or paddlewheel flow meters are mechanical meters that have a freely rotating turbine set in the path of a fluid stream.
- Ultrasonic flow meters utilize sound waves to measure the velocity of a fluid from which the volumetric flow rate can be calculated.
- Vortex flow meters use an obstruction, known as a bluff body, in the flow stream to create downstream vortices which are alternately formed on either side of the bluff body.
In addition to flow meters, there are several flow accessories available, including flow indicators, flow meter monitors, flow switches, flow transmitters, and flow regulators.
When selecting a flow meter, it's important to understand the requirements of the particular application. Consider factors such as the nature of the process fluid, viscosity, cleanliness, local display needs, minimum and maximum flow rate, process pressure and temperature, chemical compatibility, and pipe size.
