FLO-CORP has compiled and written definitions for several industry terms. This list is designed to be a glossary that helps you better understand the elements of our industries. Process instrumentation is used in an extremely wide range of applications anywhere measurements are needed for media that flows or is stored in a container or tank. Many of these terms will help you understand the technologies used in such measurements.
Accuracy – The accuracy of a flow meter gives the maximum plus or minus deviation between the meter’s indication and the true value of the flow rate, or in the flow total. It is the interval within which the true value of a measured quantity can be expected to be in with a stated probability. Accuracy may also be referred to as uncertainty. Accuracy include the combined errors due to linearity, hysteresis, and repeatability. Accuracy can be stated as a percent of span or full scale, as a percent of rate, or as a percent of upper range value or upper limit value. it is important to understand the differences between the stated value.
Back Pressure – A reference to pressure as opposed to the desired flow of gases in a given pipe diameter. It is any condition where the pressure in a system becomes greater than the supply pressure. Back pressure is caused by obstructions in the pipe, pipe direction or orientation, pipe surfaces and pipe types as well as tight bends. Because of air resistance, friction between molecules, the term Back Pressure is misleading as the pressure remains and causes flow in the same direction, but the flow is reduced due to resistance. Back Pressure is often confused with Pressure Drop. Back Pressure can contributes to the release of vapor from liquid and are a function of head loss in liquid flow piping systems. This condition is often referred to as Cavitation.
Cavitation – If a liquid enters a flow meter at a pressure near its vapor pressure, the pressure reduction in the meter can cause the liquid to flash partly to a gas. If, with pressure recovery, the gas pressure rises back above the vapor pressure, the bas bubbles will implode, causing cavitation to occur. Plashing and vaccination can destroy many piping systems and many types of flow meters.
Density – The property of a fluid expressed as weight or mass per unit volume. Liquid density is generally a function of temperature. Gas and vapor density varies with changes in temperature and pressure. As an example, water has a density of 62.34 lbs. per cubic foot at 60º F. And a density of 60.13 lbs. per cubic foot at 200º F.
Flow Meter – a process instrument that measures continuous flow of media through a pipe or other vessel. The media being measured is often gas, liquid, or slurry. There are many technologies in use for flow measurement some of which include calorimetric, mass, positive displacement, turbine, ultrasonic, and variable area/volumetric. When the media has particulate matter in it, extreme heat, high pressure, or is in a low flow application, certain considerations must be made in choosing a flow meter that can fit the application.
Flow Switch – a process instrument that measures flow of media at set points as it moves through a pipe or other vessel. The media being measured is often gas, liquid, or slurry. There are many technologies in use for flow switches some of which include calorimetric, ultrasonic, and variable area/volumetric. When the media has particulate matter in it, extreme heat, high pressure, or is in a low flow application, certain considerations must be made in choosing a flow switch that can fit the application.
EMI/RFI Effect – Electromagnetic Interference (EMI), also called radio-frequency interference (RFI) when a radio in the radio frequency spectrum is a disturbance generated by an external source that affects an electrical circuit by electrostatic coupling or conduction. The electromagnetic emission will cause an undesirable response or degradation in the performances of electrical equipment. Generally produced by welders, motor starters, VF drives, radios, causing analog instruments to spike in signal. Shielding and line filters can reduce these effects.
Fluids – Fluids are normally categorized as liquids, gases or vapors. Liquids are practically incompressible and occupy definite volumes. Gases and vapors are compressible and fill any volume within a known or given pressure.
Full Bore Meter – Any flow meter that typically uses the entire flow team in making the flow measurement. Full Bore Meters can include process connections that are threaded or flanged that generally have the same process connection size as the given pipe size.
Head Loss – Every flow meter uses energy in the form of pressure, or head loss, to the system. In addition to the meter, all fittings, valves and even straight piping can affect to some degree Head Loss. The less head loss a flow meter introduces into the system the better. The portion of energy that is lost due to friction which leads to resistance to flow is called Head Loss.
Insertion Flow Meter – Any flow meter that is generally inserted into a piping system through a piping insertion port or isolation valve fabricated into the process piping system. An insertion flow meter is typically classified as any device which infers an overall flow rate based upon a single measurement of a fluid velocity taken at a strategic location inside the pipe. A typical insertion meter consists of a sensing element, support structure attachment fitting and pressure seal. Inly a portion of the flow stream is used in making a measurement, and the accuracy of the meter is based upon the assumption that a known relationship exists between the velocity being measured and the average fluid or gas velocity.
K Factor – The K factor of a flow meter is the ratio of the meter output generally in pulses to the corresponding volume total of fluid passing through the meter during a measurement period. The variation in the K factor may be presented as a function of Reynolds Number or flow rate. K factors versus Reynolds number curves can be generated by flow meter manufactures when the meter is calibrated on a convenient fluid, typically water or air. K factors can change with thermal effects on the body of the meter, or between pipe schedules.
Laminar Flow – A condition of flow when the fluid flows in parallel layers, with no disruption between the layers. Laminar Flow is the ideal flow condition in gas flow when all of the air molecules are all moving in a straight forward path down the pipe together. Efficient air flow systems should have a Reynolds Number of less than 2300.
Level Switch – a process instrument that measures set point level of media in a barrel, container, flume, tank, weir, or other vessel. The media being measured is often a liquid, slurry, or solid. Three common technologies for level switches include guided-wave radar, non-contacting ultrasonic, and vibration. When media has low dielectric constants, extreme heat, or is in an area with foam or vapor, the appropriate level switch technology must be chosen for accurate measurement and durability.
Level Transmitter – a process instrument that measures continuous level of media in a barrel, container, flume, tank, weir, or other vessel. The media being measured is often a liquid, slurry, or solid. Two common technologies for level transmitters include non-contacting ultrasonic and guided-wave radar. When media has low dielectric constants, extreme heat, or is in an area with foam or vapor, the appropriate level transmitter technology must be chosen for accurate measurement and durability.
Mass Flow Meter – a flow meter that measures using the Coriolis principle, the mass of a media which passes through the meter in a unit of time. Mass flow meters typically have a greater cost associated with them when compared to other meter technologies and are highly accurate. Typical applications for mass flow meters include gases, industrial paints, methanol/catalyst streams, and oils.
Open Channel Flow Meter – a flow meter that measures the level of flow through a channel with known dimensions. By using a flume or a weir, the level of flow can be plugged into a mathematical formula to determine flow rate. Given the way open channel flow meters measure flow rate, the meter itself consists of a level transmitter along with a process monitor that makes the conversion from level to flow rate given the other factors involved. Typical applications for open channel flow meters include effluent flows, gravity fed sewer lines, storm water monitoring, and clarifier effluent. Waste and wastewater are the primary industries served by this type of flow meter.
Positive Displacement Flow Meter – a flow meter that measures the displacement of gears or spurs as media passes through the meter. This type of measurement uses the volumetric principle of measurement by counting the gears or spurs as they move a known volume of media. These meters maintain consistent accuracy despite changing viscosity conditions and are frequently installed in brake fluid, fuel, glue, grease, oil, polymer and Skydrol applications.
Process Display – a process instrument that monitors and shows process conditions. A process display may show its measurement through a digital read out, on a scale, or through other means. A process display with have an input of data and often includes a way to output data, such as an analog loop output. Process displays come in a variety of configurations and it is important to select a display that has all the features needed for the application.
Reynolds Number – A dimensionless quantity used to predict flow patterns in liquid and gas flow systems. Reynolds Number is used to predict the transition from Laminar Flow to Turbulent Flow conditions.
Turbulent and laminar flow can be calculated as well, using the following formula to determine what is called Reynolds Number:
Re = ρvd/µ
Re is the Reynolds number.
ρ is the air density.
v is the mean velocity.
d is the diameter of the pipe.
µ is the dynamic viscosity.
Rotameter – see volumetric flow meter.
Rotometer – see volumetric flow meter.
Thermal Mass Flow Meter – a flow meter that measures continuous flow by detecting heat change in the media as it flows by the sensor. For reference, thermal mass flow meters are often used in air conditioning, dust collection, energy conservation systems, potable/non-potable water, sulfuric acid, and ventilation monitoring.
Thermal Mass Flow Switch – a flow switch that measures flow by detecting heat change in the media as it flows by the sensor. Thermal Mass flow switches are used in chemical feed systems, chiller feed water, combustion cooling systems, damper regulators, for pump protection, and ventilation.
Turbulent Flow – A condition when the flow of the fluid undergoes irregular fluctuations in flow paths or layers. The velocity or speed of the flow is moving at irregular magnitude and direction.
Turbulent flow is the most inefficient flow condition as the air molecules spend so much energy bouncing off of pipe walls, forward, reverse and sideways directions that they spend much of their energy away from moving down the pipe.
Ultrasonic Flow Meter – a flow meter that calculates flow volume of a media as it passes through ultrasound sent between meter sensors. The ultrasonic flow meter will average the transit time of the beam or measure the frequency shift using the Doppler effect to determine the flow rate. An ultrasonic flow meter is non-intrusive, meaning it is mounted outside the pipe. Since no entry is needed, mounting the meter does not require an interruption to the process. Typical ultrasonic flow meter applications are aerated liquids, dredges, plastics, pulp, sludge, slurries, and sewage.
Universal Process Display – a process display that offers a variety of features for monitoring and controlling process applications as a standard factory configuration. A universal process display typically includes communication interfaces such as RS-485 and/or Ethernet, along with outputs for controlling relays. “Universal” indicates that more features are built in to the device than a standard process display.
Variable Area Flow Meter – see volumetric flow meter.
Velocity Flow Meter – A flow meter that measures the velocity or speed of a given fluid or mass and typically infers volumetric flow rate based upon the internal area of the meter open to flow.
Volumetric Flow Meter – a flow meter that measures the volume of flow to determine flow rate. Volumetric flow meters are also commonly called variable area flow meters, rotameters, and rotometers. In FLO-CORP’s line up, we refer to our MEMFlo™ line of flow meters as our volumetric line. MEMFlo flow meters use the volumetric principle of measurement to determine flow rate and are designed with more capabilities than a classic volumetric/variable area flow meter. Our MEMFlo line of volumetric flow meters is very robust, offered in all metal for high temperatures and high pressure and is able to deal with suspended solids in the media. Classic volumetric/variable area flow meters are not able to handle particulate matter and filtering is required before media enters the flow meter. Furthermore, other meters use the volumetric principle of measurement including positive displacement flow meters and some water flow meters. Positive displacement flow meters count the gears or spurs to determine a known volume of media passing through the meter; even though these meters use volumetric measurement by design, the name refers to the way the media displaces gears or spurs to determine flow rate. Water flow meters generally rely on positive displacement (volumetric) or turbine (velocity) measurements.
Wireless Monitoring – monitoring that is accomplished without the use of wires between the device reporting data and the interface receiving data. For example, a cellular wireless device will report data wirelessly to a cell tower. The process data reported is then viewable through a web interface. In this example, wires are likely used to connect the process measurement equipment to the cellular transmitter in the field and once data reaches the cell towers wires are used to move the data. Regardless, the process involves wireless monitoring because equipment in the field can report data at some stage of the process without using hardwired connections. Wireless monitoring can use a variety of delivery methods including Bluetooth, wifi, cellular, satellite, and more. Considering another example, a level transmitter is mounted on a tank truck. The level transmitter takes regular measurements of the level in the tank truck as pickups and/or deliveries are made. At set intervals and/or trigger points, the wireless monitoring device reports via cellular or satellite data. That data is then available through a web interface. As long as the tank truck is in an area with cell coverage or has an unobstructed connection with satellite(s), data is reported through wireless monitoring. Once data is reported, it is available for viewing by logging into a web interface or software interface. Other functionality is also available through the interface including wirelessly configuring the reporting device, setting up e-mail/text alerts, GPS location (if the device is GPS capable), and other information.
Wireless Monitoring System – a device (or devices) that uses wireless communication to report process data measured by a process instrument (flow meter, level transmitter, etc). As part of the system, process data, configuration functions, and other features are then made available through a software or web interface. A wireless monitoring system is a type of machine to machine (M2M) functionality. See wireless monitoring.