Liquid flowing past the rotor turns the rotor, just as wind will turn the blades of a windmill. Each blade of the rotor is counted and registered. The more liquid flowing through the meter, the faster the rotor turns and the higher the numbers on the register. Conversely, if the flow rate declines, less liquid flows through the meter, the rotor does not turn as often, and the register indicates less volume through the meter.
accounted for by counting the revolutions of the door.
account for the discrepancy when determining true volume through the meter. A displacement meter is generally found to be more accurate than a turbine meter for measuring viscous hydrocarbons like heavy crude oil and fuel oils. Finally, slippage may allow some liquid through the meter that is not registered, but it also allows sand and sediment, in some crudes, to flow though the meter without undue damage. 6.3 Turbine Meter A turbine meter measures liquid flowing through it in a completely different way from the displacement meter. Instead of displacing the liquid stream into separate parts and measuring the number of parts, the turbine meter measures the velocity of the liquid moving through a known area (meter) and infers the volume flowing through it. Turbine meters are referred to as inferential meters, because they measure the velocity of the liquid and from that measurement infer the flow rate and thus the volume. The speed or flow rate of a liquid is directly proportional to its volume. The higher the flow-rate through a given area, the greater the volume. The basic parts of a turbine meter, including the rotor, shaped much like a windmill, the stator (hanger or diffuser), the pickup coil, and a register or indicator.
The more people who slipped through the side doors, the more inaccurate counting the revolutions would be. The same principle applies to displacement meters. In order for the rotor and blades to turn, there must be a space, or clearance, between the rotating parts and the meter housing. Some liquid slips through these clearances and is not registered.
This slippage is accounted for during regularly scheduled meter proving.
Pumping the liquid through the meter at a consistent rate is important because it keeps the amount of slippage from varying. An increase in flow rate increases the amount of slippage; a decrease in flow rate decreases the amount of slippage; maintaining a steady flow rate through the meter helps maintain a consistent rate of slippage, and thus, helps accurately account for all oil flowing through the meter. Another problem with this type of meter is wear. As the rotor turns, wear on the moving parts causes changes in the meter’s performance, clearances tend to increase, and gears and other moving parts become worn and therefore less precise. The result is that more oil or product slips through the meter unregistered. Despite these limitations, this type of meter is still used. It is regularly proved to determine just how much oil has passed through unmeasured and to
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