Liquid flow meters are used for measuring the flow or quantity of a moving fluid. They use four basic metering technologies: differential pressure (DP), positive displacement (PD), velocity, and true mass. Differential pressure flow meters obtain a liquid’s flow rate by measuring the pressure differential and extracting the square root. Examples include orifice plates, Venturi tubes, flow nozzles, Pitot tubes, target meters, elbow tap meters, and rotameters. Positive displacement flow meters divide the liquid into specific increments which are counted by mechanical or electronic techniques. These devices are often used for high-viscosity fluids. Velocity flow meters operate linearly with respect to the flow rate. Because there is no square-root relationship, their range is greater than DP devices. True mass flow meters are used to directly measure the mass rate of flow. These types of liquid flow meters include thermal meters and Coriolis meters.
Specifications for liquid flow meters include pipe diameter, mounting style, end fittings, electrical outputs, and interface options. There are three basic mounting styles: in-line, insertion, and non-invasive. In-line flow meters are installed directly in the process line. Insertion-type devices are inserted perpendicular to the flow path and usually require a threaded hole in the process pipe. Non-invasive liquid flow meters do not require mounting directly in the process flow and can be used in closed piping systems. Fittings can be flanged, threaded, or compression-style devices. Clamps, plain ends, socket welds, tube ends, and hose nipples are also available. In terms of electrical outputs, choices include: analog current, analog voltage, frequency, and switch. Some liquid flow meters provide signal outputs in serial, parallel, Ethernet, or other digital formats. Others format output signals according to industrial fieldbus, networking, or industrial automation protocols.
Liquid flow meters are used for measuring the flow or quantity of a moving fluid. They use four basic metering technologies: differential pressure (DP), positive displacement (PD), velocity, and true mass. Differential pressure flow meters obtain a liquid’s flow rate by measuring the pressure differential and extracting the square root. Examples include orifice plates, Venturi tubes, flow nozzles, Pitot tubes, target meters, elbow tap meters, and rotameters. Positive displacement flow meters divide the liquid into specific increments which are counted by mechanical or electronic techniques. These devices are often used for high-viscosity fluids. Velocity flow meters operate linearly with respect to the flow rate. Because there is no square-root relationship, their range is greater than DP devices. True mass flow meters are used to directly measure the mass rate of flow. These types of liquid flow meters include thermal meters and Coriolis meters.
Specifications for liquid flow meters include pipe diameter, mounting style, end fittings, electrical outputs, and interface options. There are three basic mounting styles: in-line, insertion, and non-invasive. In-line flow meters are installed directly in the process line. Insertion-type devices are inserted perpendicular to the flow path and usually require a threaded hole in the process pipe. Non-invasive liquid flow meters do not require mounting directly in the process flow and can be used in closed piping systems. Fittings can be flanged, threaded, or compression-style devices. Clamps, plain ends, socket welds, tube ends, and hose nipples are also available. In terms of electrical outputs, choices include: analog current, analog voltage, frequency, and switch. Some liquid flow meters provide signal outputs in serial, parallel, Ethernet, or other digital formats. Others format output signals according to industrial fieldbus, networking, or industrial automation protocols.
Liquid flow meters differ in terms of features and operating performance. As a rule, a liquid flow meter’s technology determines its ability to measure additional media such as gas, steam, suspended solids, or slurries. Media temperature is largely dependent on construction and liner materials. Liquid flow meters that can measure temperature, density, or level are commonly available. They may include audible or visual alarms, averaging and controller functions, programmability, and recorder or totalizer functions. In terms of performance, turndown ratio is the effective or dynamic or operating range of the liquid 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.
