Gas and Liquid Metering

Why Metering? Measuring flow rate and cumulative volume Selling System Control Losses detection Reservoir outlets Pumping stations

Accuracy Accuracy of meters depends on:  Linearity: percentage of true reading over a stated flow  Repeatability: ability to indicate the same reading each time the same flow condition  Pressure loss  Resolution  Rangeability

Mechanism of Meters All meters are consisted of two parts:  The primary element, which is in contact with the fluid, resulting in some form of interaction.  The second or secondary element translates the interaction between fluid and primary element into a signal.

Different Types of Meters Positive displacement meter Turbine meter Orifice meter Magnetic meter Coriolis meter

Affecting Factors Fluid properties  Viscosity  Specific gravity Conditions  Temperature  Pressure Flow pattern

Positive Displacement Positive displacement meters measure the volume flow rate directly by repeatedly trapping a sample of the fluid. Positive displacement meters can be less accurate than other meters because of leakage past the internal sealing surfaces.

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Turbine Meter A turbine meter uses a multi-bladed rotor. The turbine rotation is proportional to the fluid velocity A magnetic coil outside the meter produces an alternating voltage. The voltage is then related to the flow rate. They have fast response.

Orifice Meter A concentric orifice plate The pressure between both sides of plate is related to the flow rate using Bernoulli's equation.

Orifice Meter(cont.) The simplest and least expensive Produces a relatively high pressure drop.

Magnetic Meter Insensitivity to  specific gravity  Viscosity  Pressure  Temperature Sensitive to magnetic properties of the liquid.

Coriolis Meter The Coriolis meter uses a U- tube sensor Applies Newton’s Second Law Fluid momentum changes natural vibration of the U-tube and twists it. Two sensors detect vibrating velocity of the U-tube at each side and relate it to mass flow.