Adrian Whittle asked:


Flowmeters are used in many ways but their basic aim is to measure the flow of a particular substance passing through a tube, pipe or chamber. Why would you want to do this? Well, you could say one of the reasons is to assess the well being of the machine that is being measured. Another reason may be to assess that the machine is operating correctly. This article will illustrate some of the flowmeter types and discuss how they are used.

Peak flowmeters are used to measure the rate of air flow out of the lungs. Peak flowmeters are used to assess or gauge the condition of a person’s lungs. This is sometimes used as part of a fitness test as the rate at which air can be exhales from the lungs indicates the capacity of the lungs and determines the level of physical activity a person can undertake. However a peak flowmeter is more commonly used to determine whether someone is asthmatic or is used to manage the condition once it has been diagnosed.

A peak flow meter is a common type of flow meter, in that it uses the displacement method to determine the flow rate of air. The displacement method is simply a float within a confined space like a pipe or tube. When air passes through the tube it moves the float. The distance that the float moves indicates or is a correlation of the flow rate.

In many industries, like HVAC, food processing, water management, industrial and chemical manufacturing there are needs to measure the flow of various gases and liquids through large or small machinery. For instance, the production of many processed foods is largely automated. There may be a human operator that needs tools like a flowmeter to check that the right amounts of various ingredients are going into the machine. If the wrong quantities are used the food does not taste right or may have to be recalled.

In these industries there are a variety of flowmeters. The most common are ultrasonic flowmeters and thermal dispersion flowmeters. They can measure the flow rate of gases and liquids so have plenty of applications.

The principal behind the ultrasonic flowmeter is that the change in the frequency of an ultrasonic wave can be used to correlate the flow rate of the particular substance that has caused this change. This is the same principal behind the Doppler shift flowmeter, that is commonly used to measure liquids that contain particulate matter, like effluent, waste water or reclaimed water.

Thermal dispersion has a similar idea except that it uses the change in heat from a particular heat source located within the pipe or tube. The change in heat will be directly related to the flow rate of the gas or liquid that is passing this heat source.

Other types of flowmeter include the turbine, magnetic and wheel flowmeters. Again, these devices have applications in many larger scale industrial complexes to ensure that a particular machine is working correctly or is getting the right quantity of a particular substance.

Arthur