FLOW METER

          Flow Meters

flow meter

Flow meters are used to measure the flow of air, fluids and gas. Some flow meters

measure the volume of the material while others measure the speed, and still others

measure the mass of the materials. For the most part, flow meters are used to infer mass flow through calculations the instruments make after taking various measurements such as absolute pressure, differential pressure, viscosity and temperature. Most flow meters are made up of three parts: the primary device, transducer and transmitter. These three parts are usually combined into one so that the flow meter is only one instrument. There are many different types of flow meters used for different measurements of flow. A thermal mass flow meter takes measurements with two sensors that work together. A temperature sensor reference, and an active heated sensor take measurements by calculating how much heat loss occurs in the flowing liquid, and thus can determine the flow rate based on this amount. Another type of flow meter is the Coriolis mass flow meter, which operates on the basis of the Coriolis Effect. Basically, an excitation force is

applied to the tube, causing the fluid or gas to rotate because the acceleration is acting in opposite directions on both sides of the applied force. A measurement can then be taken. Other kinds of flow meters operate using sound: these are called ultrasonic flow meters, and include several types like Doppler Effect meters and time-of-flight meters.

                 Because of their varied uses, flow meters are useful in a variety of fields. Medically, they are used to measure a patient’s air intake. This type of flow meter is called a peak flow meter and is particularly beneficial for asthma patients. In plumbing, flow meters are used to measure the amount of fluid running through a tube for efficiency purposes. In general, flow meters are used in many industrial purposes for flow measurements to help companies determine profit gain or loss. Other industries that benefit from the use of flow meters include the automotive industry, petroleum and gas industries, utility services, HVAC, food processing and raw materials industry.

               Each type of flow meter has specific guidelines that must be followed for proper use. For example, when using a flow meter for gases, the flow meter must remain full of gas. Liquid in the gas flow meter can affect the meter's accuracy. Similarly, in order for a liquid flow meter to work properly, it must remain full of liquid. Gas in a liquid flow meter can affect the meter’s accuracy as well. Generally, contaminants of any kind will cause an inaccurate reading of the flow meter, so these instruments must be treated with care and cleaned regularly.

Types flow meter and usage :

· Air flow meters are used to measure the flow of air.

· Coriolis mass flow meters are used to measure the force of acceleration resulting

from a moving object towards or away from the center of rotation.

· Differential pressure flow meters are used to measure the flow of fluids and gases

in a pipe by introducing constriction that causes the pressure to drop. The pipe

must be clean to result in accurate measurements.

· Insertion flow meters measure flow at one position in a pipe, and then, based on

the measurement, they estimate the flow rate for the entire pipe.

· Magnetic flow meters measure by creating a magnetic field that is channeled into

the liquid and causes a voltage signal to be sensed that is proportional to the flow

of liquid.

· Mass flow meters are used to measure gas flow and are one of the more popular

flow meters. This meter is relatively unaffected by changes in temperature or

pressure in the tube or pipe.

· Open channel flow meters are used to measure the flow of liquids when they are

open to the atmosphere.

· Peak flow meters are used by patients with asthma or other lung disorders to

measure the amount of air patients take into their lungs. These flow meters allow

physicians to determine the severity of the illness.

· Positive displacement flow meters trap liquid to measure its flow by rotating parts

that move between seals and the meter body.

· Rotometers have a rotating float that moves vertically through a tapered tube.

· Sight flow indicators allow the operator to view the liquid as it is moving. Some

models come equipped with lights to enhance the visibility of the fluids.

· Target flow meters measure the amount of force that is exerted on a target in a

particular liquid or gas. This should not be used to measure high viscosity liquids

because the target can be damaged.

· Thermal flow meters are meters that use thermal properties of fluids to measure

the flow. The meter is heated and as the liquid flows by, it can tell the flow rate by

the amount of heat lost.

· Turbine flow meters consist of a rotor that measures the fluid when it passes

through the blades. The blade speed is translated into the speed of the fluid

· Ultrasonic flow meters use sound to determine flow rate. Both Doppler Effect

meters and time-of-flight meters are different kinds of this type.

· Variable area flow meters measure by letting the flow stream change the opening

in the meter with a movement of an internal part.

· Vortex and fluid flow meters generate oscillations as a result of the flow that

allows a measurement to be taken.

· Water flow meters are flow meters designed for measuring flow rates of water in

various channels, tubes, partially filled pipes, streams, and rivers.