Gas Flow Meters Specifications

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Type

	Type		Differential pressure meters (DP) include orifice plates, venturi tubes, flow nozzles, cone types, Pitot tubes, target meters, elbow tap meters and rotameters. The basic operating principle of differential pressure flowmeters is that the pressure drop across the meter is proportional to the square of the flow rate. The flow rate is obtained by measuring the pressure differential and extracting the square root. Differential pressure meters have a primary and secondary element. The primary element causes a change in kinetic energy, which creates the differential pressure in the pipe. The unit must be properly matched to the pipe size, flow conditions, and the liquid's properties. In addition, the measurement accuracy of the element must be accurate over a reasonable range. The secondary element measures the differential pressure and provides the signal or read-out that is converted to the actual flow value.
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	Cone Type		Cone-type devices place a cone directly in the center of the fluid flow to create differential pressure (DP) that can be measured before and after the obstruction. DP is proportional to velocity.
	Coriolis Meter		With Coriolis meters, fluid is passed through a small vibrating flow tube. The resulting deflection of the flow tube is proportional to the mass flow rate of material.
	Elbow Tap Meter		Elbow tap meters operate on the principle that when liquid travels in a circular path, centrifugal force is exerted along the outer edges. When a liquid flows through a pipe elbow, the force on the elbow's interior surface is proportional to the density of the liquid times the square of its velocity. Typically, the device consists of a 45-degree pipe elbow in fluid flow, with high-pressure tap outside of the elbow and low-pressure tap inside of the elbow.
	Electromagnetic Meter		Electromagnetic flow meters operate on Faraday's law of electromagnetic induction, which states that a voltage is induced when a conductor moves through a magnetic field. The liquid serves as the conductor; the magnetic field is created by energized coils outside the flow tube.
	Flow Nozzle		Flow nozzles are similar to Venturi tubes, but the nozzle opening is an elliptical restriction in the flow. There is no outlet area for pressure recovery, and pressure loss is comparable to an orifice plate. Flow nozzles can handle both clean and dirty fluids; however, viscosity can pose a problem through a constricted orifice.
	Laminar Flow		Laminar flow elements consist of a tube bundle or parallel plates. They are used to measure flows with low Reynolds numbers. The differential pressure across this type of flow meter is linear with the flow.
	Nutating Disc		The pressure of the medium causes a disc to rock in a circulating path without rotating about its own axis. A pin extending from the disc is connected to a counter that monitors the disc's rocking motions.
	Orifice Plate		Orifice plates are simple and cost-effective flat pieces of metal with a specific-sized, bored-in hole. They constrict the flow of a fluid to produce a differential pressure (DP) across the plate. Orifice plates tend to have a higher pressure loss than other DP meters, but can handle both clean and dirty fluids. Viscosity can be problematic through a constricted orifice.
	Oval Gear		Oval-gear meters have two rotating, oval-shaped gears with synchronized, close-fitting teeth. A fixed quantity of liquid passes through the meter for each revolution. Shaft rotation can be monitored to obtain specific flow rates.
	Paddlewheel		Paddlewheel flow meters have a paddlewheel that is inserted directly into the flow of fluid. The paddlewheel rotates freely, proportional to the fluid flow. Magnetic pick-ups are used to produce a waveform signal which is converted to an appropriate output. Paddlewheel flow meters must be mounted in a straight run of pipe. They do not offer a high degree of accuracy, but are low-cost alternatives for viscous applications.
	Piston		Incremental volumes of flow are measured via a piston.
	Pitot Tube		Pitot tubes measure the difference between total and static pressure. To determine the total pressure, a hole in the flow path is pressurized by both the flow pressure and the surrounding static pressure. A hole that is perpendicular to the flow is pressurized by static pressure alone. A transducer is used to measure the difference between the total pressure and the static pressure. When the pressure difference is determined, and the local values for pressure and temperature are known, Bernoulli's equation can be used to derive the velocity.
	Rotameter		Rotameters (variable area flow meters) consist of a tapered glass tube that is vertically positioned in the fluid flow with a float. When there is no liquid flow, the float rests freely at the bottom of the tube. As liquid enters the bottom of the tube, the float begins to rise in relation to the amount of flow.
	Sonar		Sonar is used to measure the volumetric flow rate of a process fluid. The measurement principle involves characterizing the speed at which coherent vortical structures flow past an array of pressure-based or strain-based sensors which are mounted axially along the pipe.
	Target Meter		Target meters have a physical target located directly in the fluid flow. The pressure caused by the flow hitting the target causes the target to deflect. The deflection of the target is measured by an instrument. Target flow meters can be used for any type of liquid, gas, or steam cryogenics.
	Thermal Meter		Thermal meters use a heated sensing element isolated from the fluid flow path. The flow stream conducts heat from the sensing element. The conducted heat is directly proportional to the mass flow rate.
	Turbine Meter		Turbine meters use a pipe-mounted rotor that is perpendicular to the liquid flow. The rotor spins as the medium passes through the blades. The rotational speed is a direct function of the flow rate and can be sensed by magnetic pick-up, photoelectric cell, or gears.
	Ultrasonic Meter		Ultrasonic flow meters use sound waves to determine flow rates. They can be either Doppler effect meters or time-of-flight meters.  Doppler effect meters measure the frequency shifts caused by fluid flow. The frequency shift is proportional to the fluid's velocity. For Doppler meters to work properly for a liquid, particles must be present (measuring "pure" liquids is not possible).  Time-of-flight meters use the speed of the signal traveling between two transducers that increases or decreases with the direction of transmission and the velocity of the fluid being measured.  For liquids, ultrasonic flow meters work best with a less than 10% by volume content of suspended solids or air gaps.
	Vane Meter		Vane flowmeters measure flow by using a spring loaded flap or door (vane). The vane is displaced by the flow of the media.  Measurement is determined by the amount the vane opens or rotates to allow the media to pass.
	Variable Area		Variable-area flow meters have an internal float or orifice plate that moves in relation to the flow rate. As flow rate increases the orifice size or area around the float or plate increases. Similarly, piston variable-area flow meters use a spring-opposed piston that moves in relation to the flow rate.
	Venturi Tube		Venturi tubes operate by gradually narrowing the diameter of the flow pipe and measuring the resultant drop in pressure. They can handle clean and dirty fluids, although the constricted orifice design can have problems with viscous media.
	Vortex (Shedding) Meter		With vortex (shedding) meters, the frequency of vortices shed from a bluff body placed in the flow stream is proportional to material velocity.
	Other		Other unlisted, specialized, or proprietary configurations.
	Search Logic:		All products with ANY of the selected attributes will be returned as matches. Leaving all boxes unchecked will not limit the search criteria for this question; products with all attribute options will be returned as matches.
	Pipe Diameter		The diameter of the process pipe to be monitored.
	Search Logic:		User may specify either, both, or neither of the "At Least" and "No More Than" values. Products returned as matches will meet all specified criteria.

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Performance A meter's performance can be determined by its turndown ratio. Turndown ratio is the effective dynamic or operating range of the flow meter. For example, if a 500 SCCM flow rate device has a turndown ratio of 50:1; it will operate effectively and resolve flow down to 10 SCCM. If the same device has a turndown of 100:1, then it will resolve effectively to 5 SCCM.

	Gas Volumetric Flow Rate		Gas volumetric flow rate range is the range of flow in volume/time. This specification applies to volumetric flow sensors and meters for gases.
	Search Logic:		User may specify either, both, or neither of the limits in a "From - To" range; when both are specified, matching products will cover entire range. Products returned as matches will meet all specified criteria.
	Mass Flow Rate		Mass flow range is the range of flow in mass/time. This specification applies to mass flow sensors and meters.
	Search Logic:		User may specify either, both, or neither of the limits in a "From - To" range; when both are specified, matching products will cover entire range. Products returned as matches will meet all specified criteria.
	Velocity Flow Rate		Velocity flow range is the range of flow in distance/time. This specification applies to velocity flow sensors and meters.
	Search Logic:		User may specify either, both, or neither of the limits in a "From - To" range; when both are specified, matching products will cover entire range. Products returned as matches will meet all specified criteria.
	Operating Temperature		The temperature range over which the device must operate.
	Search Logic:		User may specify either, both, or neither of the limits in a "From - To" range; when both are specified, matching products will cover entire range. Products returned as matches will meet all specified criteria.
	Operating Pressure		Operating pressure is the maximum head pressure of the process media that devices can withstand.
	Search Logic:		User may specify either, both, or neither of the "At Least" and "No More Than" values. Products returned as matches will meet all specified criteria.
	Media Temperature		Media temperature range is the maximum media temperature that can be monitored. It is usually dependent on construction and liner materials.
	Search Logic:		User may specify either, both, or neither of the "At Least" and "No More Than" values. Products returned as matches will meet all specified criteria.

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Features

	Mounting Type
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	In-line		In-line flow meters are installed directly in the process line. They have a variety of end-fittings including flanges, threads, and compression fittings. Typically, in-line flow meters require a straight run of pipe for installation.
	Insertion Type		Devices are inserted perpendicular to flow path. They usually require a threaded hole in the process pipe or another means of access.
	Non-Invasive		Non-invasive flow meters do not require mounting directly in the process flow and can be used in closed piping systems. Ultrasonic flow meters such as Doppler devices may use this type of mounting to read the flow through the pipe.
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	End Fittings
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	Clamp		Devices are inserted parallel to the flow path and clamped between two existing process pipes. External clamp-on flow meters are non-invasive. They do not require mounting directly in the process flow and can be used in closed piping systems.  Ultrasonic, or Doppler, flow meters may use this type of mounting to read the flow through the pipe.
	Compression		Compression fittings tighten down a sleeve or ferrule over a joint to prevent leakage.
	Flanged		Devices are inserted parallel to the flow path, usually between two pieces of existing, flanged process pipes. Circular or square flanges are used to connect the fitting, typically via bolting or welding.
	Plain End		Devices have a plain, straight-pipe end that can be inserted into the bell end of the connecting pipe.
	Socket Weld / Union		The end fitting is designed for welding or soldering and can be a weld neck.
	Threaded		Devices are inserted parallel to the flow path and threaded into two existing process pipes. National pipe thread (NPT) is the most common thread type.
	Tube End / Hose Nipple		Tube-end or hose-nipple is a common description for a short piece of pipe, usually with male threaded ends.
	VCO® / VCR®		VCO® and VCR® connections are proprietary, threaded fittings for vacuum applications that use the Swagelok design. VCO® fittings have an O-ring face seal.  VCR® fittings have a metal gasket face seal. VCO and VCR are registered trademarks of Cajon Company. Swagelok is a registered trademark of Swagelok Co.
	Other		Other unlisted, specialized, or proprietary configurations.
	Search Logic:		All products with ANY of the selected attributes will be returned as matches. Leaving all boxes unchecked will not limit the search criteria for this question; products with all attribute options will be returned as matches.
	Electrical Output
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	Analog Current		Analog current levels (transmitters) such as 4 – 20 mA are suitable for sending signals over long distances. A current is imposed on the output circuit proportional to the measurement. Feedback is used to provide the appropriate current regardless of line noise and impedance.
	Analog Voltage		Analog voltage outputs are simple, usually linear functions of the measurement.
	Frequency		Frequency or modulated frequency outputs include amplitude modulation (AM), frequency modulation (FM), sine waves, and pulse trains.
	Switch		The output is a change in state of a switch or a relay.
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	Interface Options
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	Serial / Digital		Flow meters can provide signal outputs in serial, parallel, Ethernet, or other digital formats. Devices with a serial/digital interface can provide a process variable for measurement, but do not include communication lines.
	Network / Fieldbus		Devices output signals that are formatted according to an industrial fieldbus protocol such as CANbus, PROFIBUS®, or SERCOS; a networking protocol such as Ethernet; or another industrial automation protocol. PROFIBUS is a registered trademark of PROFIBUS International.
	Other		Other unlisted, specialized, or proprietary interface options.
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	Features
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	Measures Density		The sensor or meter also measures density.
	Measures Level		The sensor or meter also measures level.
	Measures Temperature		The sensor or meter also measures temperature.
	Audible or Visual Alarms		Instruments have audible or visual alarms to alert users to dangerous conditions.
	Averaging / Multi-Insertion		Multi-insertion flow meters determine the flow rate by taking flow rate measurements across several points in the flow path.
	Controller Functions		Devices have or receive sensor input, provide control, (limits, PID, logic, etc.) and output a control signal.
	Programmable		Typically, programmable meters include a built-in microprocessor. They can be adjusted electronically for different materials, ranges, outputs, etc.
	Recorder / Totalizer Functions		Totalizer functions totalize the amount of material, media, or process variable controlled. A recorder function may be a datalogger that logs system or process variables and/or control commands for later viewing or analysis. A chart recorder that can plot (chart) flow history or give total flow for a given unit of time may also be available.
	Sanitary		Devices are designed for use in sanitary environments, such as in medical or food processing applications.
	Search Logic:		All products with ANY of the selected attributes will be returned as matches. Leaving all boxes unchecked will not limit the search criteria for this question; products with all attribute options will be returned as matches.

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