What is a "Flow Meter"?

Flow meters (flow sensors, gauges, and indicators) are used to monitor and measure the flow rate of liquids, gases, and partial solids. This data allows plant/facility operators to make informed decisions about adjustments, maintenance, and troubleshooting requirements for their system. There are many styles, types, and models of flow meters designed for a variety of substances and applications. Due to the scope of this topic, we will specifically cover volumetric flow meters for liquid applications. Other styles include the velocity flow meter and the mass flow meter.

Volumetric Flow Meter Industries

Food and Beverages

Food and beverages producers require flow meters to maintain food safety standards. Using a flow meter improves accuracy in blending ingredients, dosing flavorings, and general process control of ingredients. It also helps clean-in-place (CIP) systems deliver cleaning agents at their required rates.

Water Utilities

Water processing facilities require flow meters for plant-wide process control, flow measurement, monitoring, and data reports. Flow meters are used for dosing chemicals, monthly water usage readouts, and more.

Chemicals

Precision is key when working with corrosive, viscous, and abrasive chemicals. Making sure the right amount of fluid is delivered at the right time and done in the right way is one of many vital functions of flow meters. They can withstand the harsh chemical environments, while providing reliable measurements of liquids, gasses, and steam.

Types of Volumetric Flow Meters

Volumetric flow meters measure the volume of the fluid flowing per unit of time. There are several types of volumetric flow meters: electromagnetic, ultrasonic, positive displacement, turbine, and vortex. Let us go over the unique characteristics each type has.

Vortex Flow Meter

Vortex flow meters operate under the Kármán vortex street principle. It places a dimensioned bluff (also known as a shedding bar or a bluff body) in a fast-flowing stream. The fluid will alternately shed (separate) into two downstream sides around the object and begin to curl back on itself. This curling action forms vortices (also known as eddies or whirlpools). As the vortices begin oscillating, a sensor picks up the oscillation rate frequency and turns it into an electrical pulse. The frequency of the vortex shedding is directly proportional to the velocity of the fluid.

Vortex flow meters have an accuracy of +1% of the flow rate. They can handle high pressures of liquids, gasses, steam, and corrosive materials. 

Advantages:

• Easy installation and maintenance 

• No moving parts 

• Wide flow turndown range 

Limitations:

• Not suitable for highly viscous products 

• Poor temperature resistance 

• Clean fluids only 

 
Electromagnetic Flow Meter

Electromagnetic flow meters (also known as mag meters, electromag meters, or magnetic flow meters) operate by applying Faraday's Law of Induction. This type of flow meter requires the fluid being processed to be conductive. Excitation coils in the meter will generate a magnetic field perpendicular to the flow’s direction. When the liquid passes through the meter the conducting fluid induces a voltage. The electrodes will detect this and send a voltage signal to the transmitter. The amount of voltage produced is directly proportional to the velocity of the fluid. The transmitter processes the signal and converts it into a flow rate value.

Electromagnetic flow meters have an accuracy of ±0.5% of the flow rate or better. These meters can handle processing dirty, corrosive, and abrasive fluids. They produce no pressure drop and contain no moving parts. 

Advantages: 

• High accuracy 

• No moving parts 

• No pressure drop 

Limitations: 

• Product must be conductive (please check the fluid conductivity requirements of the meter) 

• Must shield and apply proper grounding from external electromagnetic fields 

• since this type of flow meter operates by using a magnetic field, it can be interrupted by other electromagnetic fields generated by equipment such as, VFDs, motors, and more. 

IZMAG Electromagnetic Flow Meter

Our IZMAG Electromagnetic Flow Meter can handle all conductive media with a ± 0.2% accuracy. This includes but is not limited to cream, beer, sauces, and syrups. It's PFA liner provides a high level of protection against strong vibrations, pressure surges, cleaning chemicals, moisture, and corrosion.

The IZMAG is 3-A compliant, and in accordance with standard 28-04. 

Ultrasonic Flow Meter

Ultrasonic flow meters operate by applying two methods: Doppler Effect (also known as Doppler Shift) or Transit-Time. Both methods have two ultrasonic transducers, one acting as a transmitter and the other as a receiver.

The Doppler method requires dirty fluids (gas bubbles or solids) to be present. It transmits ultrasonic waves (acoustic vibrations) which reflect off moving particles or bubbles present in the fluid and cause movement. This movement causes a shift in the frequency of the ultrasonic wave, which then gets detected by the receiver. The change in frequency is then used to calculate the velocity of the fluid.

The Transit-Time method requires clean fluids to operate correctly. It measures the time it takes for an ultrasonic signal transmitted to cross a pipe and be received. A differential comparison will be made for downstream and upstream measurements. It takes those measurements to calculate the fluid’s velocity. 

Ultrasonic flow meters have an accuracy within ±1% of the flow rate. They are clamped onto the outside of the piping, making them non-intrusive to the flow. They require minimal maintenance since they have no moving parts, and last longer. 

Advantages: 

• Non-intrusive 

• No moving parts 

• High accuracy 

• Bidirectional 

Limitations: 

• Expensive 

• Requires a power source 

• Can be affected by temperature, turbulent flow, and non-uniform piping 

Positive Displacement Flow Meter 

Positive displacement flow meters (also known as oval gear meters, nutating disc meters, spur gear meters, variable area flow meters, screw meters, oscillating piston meters, helical gear meters, and rotary vane meters) use a moving blade or gear against a uniform chamber wall to trap specified volumes of fluid. The fluid flows into a chamber, of known volume, as the chamber passes through the meter an electrical pulse is created to register the fluid’s volume before passing. The gear or blade then drives the fluid to exit the chamber before continuing this process again. The number of times a chamber is filled determines the fluid’s velocity and volume. 

Positive displacement flow meters have an accuracy ±0.1% of the flow rate. They aren't affected by temperature, pressure, or viscosity changes making them suitable for measuring highly viscous fluids such as syrups, slurries and sauces.

Advantages: 

• High accuracy 

• Doesn’t require a power supply 

• Not affected by temperature, pressure, or viscosity changes

Limitations: 

• Wear and tear due to its mechanical moving parts 

• Pressure drops 

Turbine Flow Meter

Turbine flow meters use mechanical motion to determine the fluid’s velocity. They are placed directly in the pipe’s stream to allow the fluid to flow through the meter. The flow causes the magnetic multi-blade rotor or turbine to spin. Each rotation of the rotor or turbine generates an electrical pulse when it passes by the magnetic pick-up point outside of the meter. The higher the flow rate, the faster the rotor turns, and the greater number of pulses generated by the magnetic pickup. 

Turbine flow meters have an accuracy 0.5 to 2% of the flow rate depending on the quality of the meter and the flow range. They have a lower pressure drop and can handle a wide range of temperatures and pressures. 

Advantages: 

• Low pressure drops 

• Repeatability 

• Wide flow range

Limitations: 

• Sensitive to viscous, contaminated, corrosive, or bubble-filled liquids 

• Requires regular maintenance (especially on the rotor blades to prevent buildup or damage) 

HM Turbine Meter with display

The HM 1 ½ Turbine Meter is capable of handling non-conductive fluids and aqueous media with a ±0.5% of accuracy. This includes but is not limited to, salt solutions, alcohols, acids, demineralized water, and exhaust condensate. It uses a unique non-contact pulse measurement system created by a signal probe generating an electromagnetic field that interacts with the rotating turbine rotor blades. It is extremely durable against temperature, vibration, steam blowdowns, autoclaving, and aggressive fluids.  

The HM Series is 3A compliant, in accordance with standard 28-03. 

FLOWMEC G2 Series Flow Meter

The G2 Series is a battery-powered turbine flow meter that is capable of handling both corrosive and non-corrosive liquids with an accuracy of ± 1.5% - 0.75% (size dependent). This includes, but is not limited to, water, fuels, solvents, acids, and petroleum-based chemicals.  

The G2 Series is FM approved, IP65 and NEMA 4x rated, and is IECEx, CE, and ATEX certified. 

FLOWMEC TM Series PVC Water Meter

The TM Series is a battery powered water meter that is engineered for water applications with an accuracy +/- 3.0% (accuracy can be improved with field calibration). The TM Series works well for irrigation systems, cooling towers, and water treatment plants.  

The TM Series is IP65 rated, CE and UKCA certified, and RoHS compliant. 

Truflo TK3B Series Flow Meter

The TKB series is a battery powered inline paddlewheel flow meter that is capable of handling both corrosive and non-corrosive fluids with a +/- 0.5% accuracy. This includes but is not limited to water, chemicals, and other non-viscous clean fluids. The TKB has high resistance to corrosion, outdoor weathering, radiation, heat sterilization, and chemicals. It has a low pressure drop, and a backlit LCD display that rotates 360°. 

The TK3B Series is IP66 and NEMA 4x rated.

Factors Affecting Flow Measurement Accuracy

To accurately troubleshoot a flow meter, you must know the type and the model being used. Please refer to the manufacturer's documentation to narrow down the potential causes. We will list the most common causes for flow meter inaccuracy. 

Calibration Error 

Flow meters must be calibrated to handle the specific temperatures, pressures, density, and viscosity of the fluids being processed. A meter’s calibration can be off if it was incorrectly calibrated in the factory, settings have drifted over time, or if it's being used on unexpected fluid types. To keep your calibration accurate, make sure it is tested on a regular basis. 

Improper Installation 

Before installing your flow meter, ensure that there is no electrical noise, undiagnosed turbulence, bubbles, or pressure drops caused by the pipe or other structures. The line in which the meter is installed must be full at all times for accurate measurement.  It is best to install the meter in a vertical orientation with the flow proceeding upwards. 

Product Buildup 

Without proper maintenance buildup can occur. It can appear as scaling on piping, and suspended matter and sediment in the fluid. This can cause obstruction to flow, clogging, and noise interference. 

Conclusion 

Volumetric flow meters are used to calculate a fluid’s flow rate. They provide plant-wide process control and deliver accurate data to maintain industry safety standards. 

There are several volumetric flow meters to choose from: electromagnetic, ultrasonic, positive displacement, turbine, and vortex. Knowing the fluid being processed, electrical requirements, and piping requirements are a few factors to keep in mind before choosing a flow meter. However, flow meters can provide inaccurate readings if you do not have been selected and sized properly. They can also read incorrect if they aren't properly setup in the piping, have outside interference, or are incorrectly calibrated. Regularly testing flow meters for undiagnosed turbulence, pressure drops, and piping for product buildup will help plant operators maintain accurate readings. 

Please contact us for assistance in selecting and installing the correct flow meter for your application.