When man first needed to measure the flow of liquids or gasses the need for extreme accuracy to very small tolerances was not what it is today. It was acceptable that flow measurement devices would impede the flow of the liquid or gas being measured to some extent. If the accuracy was plus or minus a couple of gallons this was not a big issue.

As we became more technologically advanced we not only needed greater accuracy we had to invent new units of measurement that were incredibly smaller than the units of measurements we had just a century ago. Some of the units of measurement for flow rate today are so small it would take a microscope to detect an single unit in the new measurement forms.

In response to the need for increased accuracy and flow meters that do not affect the flow rate in any way new methods of flow measurement had to be invented. These new devices for measuring flow rate not only have to measure flow in smaller units but also need to compensate for temperature and pressure. Mechanical devices can in no way perform these types of task and electronic devices were created to fill this need.

Magnetic flow meters are the most common type of flow meter next to the mechanical types. The basic operations of a magnetic flow meter is to apply a magnetic field to the metering tube that results in a difference that is proportional to the velocity of the liquid through that tube. The magnetic flow meters work with a conducting liquid such as water.

An ultrasonic flow meter measures volumetric flow and requires that bubbles or some type of particulate exist in the stream. These are ideal for waste water or other type of dirty water and no part of this type of flow meter will impede the flow rate as you have with the mechanical types. This style of flow meter "listens" for sound caused by the particulates or bubbles. In some cases they can be used with clean water (such as distilled water) by introducing bubbles in the flow.

Coriolis flow meters are designed to measure mass flow rather than volumetric flow. The general operating principle is that fluid is passed through one or more vibrating tubes (usually "U" shaped) the fluid accelerates as it reaches the point of maximum vibration then the fluid will begin to decelerate as it leaves this point. This acceleration/deceleration causes a twisting motion that can be measured and correlated to ascertain the mass flow.

There are many other types and sub-types of flow meters. These three pages of articles are only intended as an introduction to flowmeters. We encourage you to use resources we link to from this site and others you find on your own to gain insight into the type of flow measurement tools you actually need.