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The inherit invisibility of air can be of concern to anybody utilizing compressed or hydraulic air systems. Without exact testing measures it is often impossible to determine if your system has a leak, which can literally cost millions of dollars each year. To assist in accurate testing and measuring of your systems there are a number of devices that may be used to manage both your air and gas flow measurement and control.
Proper use of flow meters will help you determine if a leak is occurring and therefore be fixed. They can also measure total compressor performance preventing system failures and continues proper operations.
With airflow demands, a simpler air flow meter is better in the case of a mechanical meter. No batteries are required for operation; there’s no software to code or update; the volume of air that escapes from a precision machine orifice can be determined with a high degree of accuracy. As that indicator never alters, over the years the same result can be expected. Any measurable drop or increase to the predetermined rate is a sign of trouble.
With magnetic flow meters, accuracy is the main attraction. Used mostly for liquid velocity measurement, these are versatile instruments that allow for the volumetric flow to be inferred. Faraday’s Law of electromagnetic induction is the key to a magnetic flow meter. When a conductive liquid moves through a magnetic filed, electrodes that are located on the wall of the flow tube itself generate a voltage signal. More voltage is generated when the fluid is fast moving, with the voltage indicator being in direct proportion to the flowing liquid’s movement. The voltage signal is then processed by a transmitter, which determines the flow of the liquid.
Varied Use of Various Meters
Flow meters range from orifices to venturies, nozzles and rotameters, pitot tubes, calorimetrics, turbine, vortex, electromagnetic, Doppler, ultrasonic, thermal and coriolis. The most common principles for metering the flow of fluids include differential pressure, open channel, positive displacement, mass and velocity.
Differential pressure flow meters include Flow Nozzles, Orifice Plates, Venturi Tubes and Variable Area Rotameters. The Bernoullis Equation is used to determine the flow by measuring the pressure drop over obstructions inserted into the flow itself.
Flow Nozzles: Most often used in industrial applications to measure air and gas flows. They are available in many materials, relatively inexpensive to install and may be used in a broad range of applications.
Calorimetric Flow Meter: Used for fluid flow measurement, the operation is based on two temperature sensors that are in close contact with the fluid. They are thermally insulated, one from the other. The flowrate itself is monitored through one of the two sensors constantly being heated. The cooling effect of the fluid on that sensor results in the analysis. As there is a constant temperature difference between the two sensors, heat energy is drawn from the heated sensor and the temperature difference between the two sensors becomes reduced when the fluid flow increases. The reduction is therefore proportional to the fluid’s flow rate.
Coriolis Flow Meter: Uses the Coriolis Effect to measure the amount of mass that moves through the element. A U-shaped tube is used that vibrates in an angular harmonic oscillation. The tubes deform and an additional vibration is added to the oscillation. These causes a phase shift on some places of the tubes and sensors then make the measurements. These flow meters can also be used to measure fluid density and, due to their direct mass measurement capabilities, sets them apart from other technologies.
Ultrasonic Doppler Flow Meter: Increases the returning signal’s frequency as fluid moves toward a transducer. The opposite is true when the fluid moves away from the transducer. The frequency difference is then used to calculate the fluid flow speed.
Open Channel Flow Meters: Measures the height of the liquid as it passes over a flume or weir obstruction placed in the channel.
Velocity Flow Meter: Calculates the speed in one or more points in the flow.
Vortex Flow Meter: An obstruction is placed in the downstream flow. The Vortex shedding occurs at a critical fluid speed and the alternating low-pressure zones cause that obstruction to travel towards the low-pressure zone where sensors then gauge the strength of the vortices and the flow is then measured.
To ensure your plant’s use of the appropriate technology, make certain all of the relevant choices are studied and tested before application. Sometimes the least expensive route is proper and, other times, the higher end flow meter is the best solution. A knowledgeable plant manager is one who can ensure the best tools are applied to the demanding projects at hand.
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