BACKGROUND Technical Field
Various embodiments may relate generally to flow meters, and particular embodiments may relate to methods and systems for diagnostic testing of flow meters.
Fluids, such as natural gas, may be transported, distributed, and/or sold to customers through a system of transmission and distribution lines. For purposes such as billing and inventory control, for example, gas metering systems may be installed at various locations along these gas lines. Gas metering systems may measure the volume of gas that flows through a particular gas line. Some gas metering systems include a gas meter and an electronic or mechanical volume corrector.
One type of gas meter is a rotary gas meter. In some rotary gas meters, gas flowing through the meter causes a set of impellers to rotate within a cylinder. This type of meter is normally referred to as a rotary positive displacement meter. As the impellers turn, they measure a displaced volume of gas that is fixed and determined by the area between the impeller and cylinder. Each impeller rotation indicates that a certain volume of gas has flowed through the meter. This is normally referred to as “actual” volume as measured by the primary flow element that is in this case a rotary positive displacement meter. Buying and selling of natural gas typically requires that the actual volume be converted to “standard” volume to account for the contraction or expansion of gas due to varying gas pressure and gas temperature. In general, these effects may be described by Boyle's and Charles' Law. To convert actual volume to standard volume, some gas metering systems use an electronic volume corrector to correct actual volume measurement originating from the rotating impellers to account for temperature or pressure of the gas in the meter.
In general, the performance of a meter is unlikely to improve over time, as bearings in the gas meter become worn or contaminated, for example. As bearing friction increases, for example, volume measurement accuracy of a rotary flow type meter may decrease as gas leaks around the impellers. To monitor the meter performance, performance standards for a particular meter may be identified when the meter is installed, for example. Over the life of the meter, the meter's performance may be compared to the initial standard.