Recent advances in flow sensing have resulted in more accurate, durable, and economical meters. Increasingly important is the ability to interface meters with a computer for instantaneous flow readout to remotely control flow, or to allow unattended process operation. To meet such demands, new types of flowmeters are being introduced, and older designs are being improved and updated. Prime considerations when selecting a flow sensor include: the type of fluid being measured, its temperature and pressure, viscosity, conductivity, corrosiveness, and cleanliness. Equally important are the requirements of the sensor itself: Flow velocity range, accuracy, ease of installation, and maintenance requirements. Finally, cost can be a major factor in the decision. Two basic classes of flowmeters are differential producers and linear flowmeters. Differential-producer flowmeters create a restriction in the flow field. When flow is contracted, either gradually or abruptly, kinetic energy increases at the expense of potential energy (static pressure). The difference between pressure at the full pipe section and that in the vicinity of the contraction is related to the square root of the velocity at the full section minus the square root of the velocity at the contraction. Fluid properties and the abruptness of the contraction also play a role in the operation of these meters. General range is 4:1. The pressure/flow relationship depends on the length and condition of the reference piping, pressure tap locations, and the geometry of the restricting element (differential producer). Any change in these characteristics alters the relationship, making these devices extremely sensitive to installation conditions. The greatest disadvantage to this class of flowmeters is that they require a secondary measuring system -- flow is determined based on a pressure-flow relationship. flow sensors are the most widely used of the differential pressure flow sensors; others being nozzle, venturi, and flow tube. Generally, an orifice sensor
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Velocity Flow Switches
Gas flow switches and liquid flow switches, velocity, are used to measure the flow or quantity of a moving fluid in terms of velocity, such as feet per minute.
Mass Flow Switches
Mass liquid flow switches and mass gas flow switches are devices used for measuring the flow or quantity of a moving liquid or gas in terms of a unit of mass per unit time, such as pounds per minute. These devices may be sensors with electrical output or may be stand-alone instruments with local displays and controls.
Liquid Flow Meters
Liquid flow meters are used to measure the volumetric flow rate or amount of a moving liquid.
Flow meters (flowmeters) and flow sensors are devices used for measuring the flow rate or quantity of a moving fluid or gas.
Volumetric Gas Flow Switches
Volumetric gas flow switches are devices with a switch output used for measuring the flow or quantity of a moving gas in terms of a unit of volume per unit time, such as cubic feet per minute.
Topics of Interest
Laminar flow elements, also known as LFEs, laminar flowmeters, or simply
laminar meters, are used to measure the flow of gases through closed conduits.
They operate by producing a differential...
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...
For many years differential pressure types of flowmeters have been the most
widely applied flow rate measuring device for fluid flows in pipes that require
accurate measurement at reasonable cost.
Velocity meters operate linearly with respect to the volume flow rate. Because there is no square-root relationship (as with differential pressure devices), their range ability is greater. Examples of...
With few exceptions, the purpose of a flowmeter is to generate a signal that is
directly proportional to flow rate. Certain types of flow signals are not necessarily
proportional to flow, i.e., they...