The need to measure the flow rate in a pipe or tube has many aaplications for individuals and in business. Generally, gases and liquids need to be measured. there are two ways to do this. The volumetric flow rate is a measure of the volume of the medium by time. The mass flow rate is a measure of the mass of the medium by time.
Flow meters can be used in many ways. Some of these ways apply to individuals, like the peak flow meter that measures lung capacity and can help asthmatics to know if an attack is likely to occur.
Other than that, flow meters are used in many industries, like the food processing industry, water management, semi conductor fabrication and many others. This article will give a brief overview of how flow meters work.
There are a wide variety of types of flow meters. They are generally classified by what they do or how they operate. For instance, a mass flow meter is a general classification of flow meter that determines the flow rate of a medium in terms of mass even though the operating principles for each meter may be different.
The Coriolis flow meter in an example of the principle determining the name. The Coriolis effect is the force that a liquid experiences in a circular motion. In the flow meter, vibrating pipes cause the liquid to move in a circular motion. If the wave motion of the vibrating pipes is known before the liquid passes through the pipes then the flow rate of the liquid can be determined.
Ultrasonic and Doppler shift flow meters also use the changes caused to sound waves to correlate a rate of flow for the medium passing through the meter.
In the case of the ultrasonic flow meter, two transmitters of ultrasonic sound waves are placed at the ends of a pipe where the measure is to take place. Each transmitter sends a pulse of sound.
The transmitters also act as a receiver of the wave sent by the other transmitter. One pulse of sound is sent in the direction of the flow and the other is sent against the flow.
Provided some information is known about the type of pipe used and a few constants for the liquid or gas, then the flow rate can be determined from the time difference of each wave.
Doppler shift meters use a sound wave that bounces off matter in the medium passing through the pipe. Due to the Doppler effect, the frequency of the waves changes when it strikes a moving object. This change in the frequency can be used to determine the flow rate of the medium passing through the pipe.
A more traditional type of flow meter is the variable area flow meter that uses a float in a calibrated tube. When a substance passes through the tube, the float is displaced by the flow.
The float indicates a measurement on the calibrated tube. This is a correlation of the flow rate of the substance that has just passed through the tube. An example of such a device is the peak flow meter that is used to measure lung capacity. Peak flow meters help people with asthma determine if they are likely to have an asthma attack.
