Flow gauges can be found wherever gas or liquid flow is involved in the function of a product or system. Often used interchangeably with flow meters, flow gauges are measuring devices that people in various industries use to track the rate at which a gas or liquid flows through a system. The goal of flow gauges is to measure and relay flow rate via readable information to an operator, so that he or she can make ascertain that all is well, or make adjustments as needed. They are essential to manufacturing processes and medical, food processing, chemical, energy, automotive, marine, plumbing, heating and cooling applications and more. A few common applications for which flow gauges are used include the tracking of fuel usage, the overseeing of exact material feed values of manufacturing processes and the monitoring of medical treatments.
Generally, flow gauges are divided by the units of measurement that they use. In addition, they are primarily divided by whether they deal with mass flow or volumetric flow. To this end, manufacturers often will hear them divided into the categories of “mass flow gauges” and “volumetric flow meters.” The difference in what these two measure is fairly self-explanatory–a mass flow gauge measures the mass of the fluid passing through a system, while a volumetric flow meter measures the volume of the fluid passing through a system.
There are two principle types of mass flow gauges, or mass flow meters: coriolis flow meters, also called inertial mass flow meters, and thermal mass flow meters. Coriolis flow meters are named after the Coriolis effect, which it uses to make its mass flow measurements. The Coriolis effect, activated by vibratory forces, causes oscillations inside flow gauge tubes; the phase shift, frequency and amplitude of these oscillations are measured by sensors attached to tubes and used to calculate mass flow rates. Thermal mass meters, on the other hand, determine mass flow rates using heat transfer principles. They are made up of a heating element and one or more temperature sensors, spaced out along the length of a tube. As the fluid used in the system passes by said heating element, it picks up thermal energy, which increases its temperature. By measuring how much of the heat is dissipated, the temperature sensor or sensors offer information that can be used to calculate the system’s flow rate. The heat transfer principle used here maintains that faster moving flows have a greater cooling effect.
Examples of volumetric flow meters include turbine and ultrasonic flow meters. Turbine flow meters measure volumetric fluid flow via the use of axial turbines. This turbine is usually located at the center of of a pipeline, aligned with the pipe’s axis. When fluid passes through the pipeline, it touches the turbine and passes on some of its energy onto the turbine’s blades, causing it to spin. The speed of this spin is then measured. The fluid flow rate of the pipeline system can be calculated using a formula that expresses the relationship between the flow rate and the speed at which the turbine spins. Ultrasonic flow meters, which are available in both single and dual sensor models, use sound to determine flow rate. The basic principle with which they operate is the Doppler Effect, which refers to the shift in frequencies that occurs when an ultrasonic signal reflects the sudden stillness of bubble or particles in motion. They work by sending ultrasonic sound through a transducer into a pipe with flowing liquids. Once inside, they bounce off of the solid particles and air bubbles inside the liquid, creating a slightly different frequency that is directly proportional to the liquid flow rate. Meanwhile, a second transducer measures the frequency of the reflecting waves and reports the system, allowing the gauge to accurately measure flow rate. Unlike many flow gauges, ultrasonic flow meters can be installed outside of the tubing or piping system. They are best for use with applications that require chemical compatibility, low pressure drop and little maintenance.
Both mass and volumetric flow gauges operate using the same basic procedures and mechanisms, though they do display some differences. These differences are based on the how they measure the flow, as dictated by the application. For example, flow may be measured using pressure-based operations, mechanical operations, thermal operations or optical operations. To determine which type or types of flow gauges are best for an application, a customer must know the requirements and settings of his or her application well. This way, he or she can effectively communicate needs to a manufacturer, who can then guide the customer to the right category and type of flow gauge.