Flow Meters

Most flow meters are made of the primary device, a transducer and a transmitter. These three flow meters parts are usually combined so that the flow meter is one complete instrument. Flow meters vary in terms of measuring technique and design and are therefore used across many fields and industries. Certain flow meters are manufactured using specific materials in order to maximize results. The cleanliness of the air, fluid or gas is an important factor as is the viscosity. The process pressure, process temperature and size of the pipe should also be taken into account. Manufacturers understand how important flow meters are to everyday industrial processes. Flow meters are used for efficiency purposes and to help companies determine profit gain or loss. Industries that benefit from the value of flow meters include the automotive, petroleum, gas, utility services, HVAC, food and beverage processing, chemical and raw material industries.

Some of the most popular flow meters are: peak flow meters, water flow meters, fuel flow meters, air flow meters, ultrasonic flow meters and flow monitor services. Many flow meters measure the volume of the material while other flow meters measure the speed, and still other flow meters measure the mass of the materials. For the most part, flowmeters are used to infer mass flow through calculations that flow meters and flow monitor instruments make after taking various flow measurements, such as absolute pressure, differential pressure, viscosity and temperature. Flow switches, however, typically have a fourth component that serves as a switching unit to control flow. They may also trigger a visual or audible alarm. Flow indicators, which are observation windows in industrial processing lines, aid in measuring flow by visual indicators. Vortex flow meters measure the flow rate by placing an obstruction directly in the flow path, forcing liquids or gases to move around it. When the flow moves around this obstruction, or bluff body, two symmetrical vortices are created on the opposite side, changing the pressure of the flow. A sensor is placed between these vortices to measure these changes in pressure, transmitting this data to an electronic signal conditioner outside the meter.

Flow meter distributors manufacture various instruments for different measurements of flow. Thermal mass flow meters take 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 these flow meters can determine the flow rate based on this amount. Another type of flow meter is the Coriolis flow meter, which operates on the basis of the Coriolis Effect. In the Coriolis Effect, an excitation force is applied to the flow meter tube, causing the fluid or gas to rotate because the acceleration is acting in opposite directions on both sides of the applied force. A flow meter measurement can then be taken. Other kinds of flow meters operate using sound: these are called ultrasonic flow meters. Another type of flow meter is an electromagnetic flowmeter, which is a type of volumetric flow meter that functions based on Faraday's law of electromagnetic induction. Also, there are rotometers, which utilize a rotating float that moves vertically through a tapered tube. Most of these designs and types are mounted in one of the three basic mounting styles: in-line, insertion and non-invasive.

Flow meter manufacturers offer various instruments for different measurements of flow and there are four main categories of air flow meters that are identified based on how they obtain a reading of the flow rate or quantity of air. Differential pressure air flow meters are the most common type. These devices take both a primary and a secondary measurement and report the difference. The first measurement causes a change in kinetic energy by directing the air through a hole in the flow meter which is measured by the second element. Positive displacement meters separate the air flow into specific volumes which are then counted. Vanes, gears, pistons, or diaphragms are commonly used to divide the air which is counted mechanically or electronically. Velocity air flow meters use a depth measurement and the average air velocity of the flow to produce a reading. They have a greater range than differential pressure devices. The last category is true mass air flow meters. They directly measure the mass of the fluid, not the volume. Each type of flow meter has specific guidelines that must be followed for proper use. For example, when using gas flow meters, the flow meters must remain full of gas. Liquid in gas flow meters can affect the flow meter's accuracy. Similarly, in order for liquid flow meters to work properly, they must remain full of liquid. Gas in liquid flow meters can affect the accuracy of flow meters' readings, as well as contaminants of any kind.

Images Provided by Sierra Instruments

Flow Meter Types

• Air flow meters are used to measure the flow of air.
• Coriolis 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.
• Electromagnetic flowmeters 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.
• 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.
• 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.
  
• Flow switches are used to monitor fluid or gas flow while it is passing through its valve body, then to send an electrical control sign if the flow rate is too high or too low. 
• Flowmeters are used to measure the flow of air, fluids and gases.
• Fuel flow meters are ultrasonic, turbine or positive displacement flow meters which measure fuel usage rate and remaining fuel quantities in transportation devices and stationary pumps.
• 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.
• 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 flow meters calculate flow rate by measuring the differential pressure of vortices created downstream from a partial obstruction, or "bluff body"; they are highly resistant to vibration and are often used in harsh environments.
• Water flow meters are flow meters designed for measuring flow rates of water in various channels, tubes, partially filled pipes, streams, and rivers.

Flow Meter Terms

Absolute Pressure - Atmospheric pressure plus gage pressure in flow meters.

Accumulator - Area where fluid is under pressure and stored as a source of power within flow meters.

Bluff body - An obstruction, often wedge-shaped, placed in the middle of a gaseous or liquid flow designed to create a downstream vortex in vortex flow meters as a means of measuring flow rate.

Control Point - The temperature flowmeter instruments need to maintain to perform designated functions of flow meters.

Coriolis Force - The force that occurs when a mass has a velocity moving outward in a rotating plane of flow meters.

Counter Weight - A mass that is added to a particular substance to create a more balanced and stable apparatus for flow meters.

Current - The flow rate of electricity within flow meters.

Density - A substance's mass per unit of volume in flow meters.

Flow - The travel of materials in response to a force, such as pressure within flow meters.

Flow Nozzle - A constriction made of a contoured plate that forms a hole in flow meters for the flow stream so a flowmeter measurement can be taken.

Flow Rate - The velocity of flow in flow meters.

Head-Loss - The loss of pressure in flow meters or a flowmeter system that is measured with a length parameter (such as amount).

Hot-Tap - Allows for flow meters to be inserted or removed without causing a complete system shutdown.

Integrator/Totalizer - A flow meters device that measures the total flow of fluids.

Manometer - Measures fluid pressure. This is a U-shaped flowmeter tube containing liquid which adjusts with the pressure in the flowmeter tube.

Mass Flow Rate - The volumetric flow rate of a liquid or gas times its density, expressed as pounds per hour or kilograms per minute in flow meters.

Potential Energy - The potential of energy when a liquid is in a position or height above a flowmeter place to which it can potentially flow.

Transducer - The part of flow meters that sense fluid as it passes through the flowmeter device.

Transmitter - The part of flow meters that produce the usable flowmeter information from the transducer of flow meters.

Weldolet - A connection for a metal pipe that is used to aid as a fitting for insertion-type sensors or flow meters.