Gas meter is designed for measurement of the volume of fuel gases such as natural gas (CNG), LPG gas and propane. Gas meters are used at residential, commercial, and industrial buildings that consume fuel gas supplied by a gas utility. Gases are more difficult to measure than liquids, as measured volumes are highly affected by temperature and pressure. Gas meters measure a defined volume, regardless of the pressurized quantity or quality of the gas flowing through the meter. Temperature, pressure and heating value compensation must be made to measure actual amount and value of gas moving through a meter.

Types of Gas Meter Designs

Several different designs of gas meters are in common use, depending on the volumetric flow rate of gas to be measured, the range of flows anticipated, the type of gas being measured and other factors.

  • Diaphragm/Bellows Gas Meters – These are the most common type of gas meter, seen in almost all residential and small commercial installations. Within the meter there are two or more gas chambers formed by movable diaphragms. With the gas flow directed by internal valves, the chambers alternately fill and expel gas, producing a near continuous flow through the meter. As the diaphragms expand and contract, levers connected to cranks convert the linear motion of the diaphragms into rotary motion of a crank shaft which serves as the primary flow element. This shaft can drive an odometer-like counter mechanism or it can produce electrical pulses for a digital gas flow computer. Diaphragm gas meters are positive displacement gas meters.
  • Rotary Gas Meters – Rotary meters are highly machined precision instruments capable of handling higher volumes and pressures than diaphragm meters. Within the meter, two figure “8” shaped lobes, the rotors (also known as impellers or pistons), spin in precise alignment. The rotational movement of the crank shaft serves as a primary flow element and may produce electrical pulses for a flow computer or may drive an odometer-like counter.
  • Turbine Gas Meters – Turbine gas meters infer gas volume by determining the speed of the gas moving through the meter. Because the volume of gas is inferred by the flow, it is important that flow conditions are good. A small internal turbine measures the speed of the gas, which is transmitted mechanically to a mechanical or electronic counter. These meters do not impede the flow of gas, but are limited at measuring lower flow rates.
  • Orifice Gas Meters – An orifice gas meter consists of a straight length of pipe inside which a precisely known orifice affects the flow. Orifice meters are a type of differential meter, all of which infer the rate of gas flow by measuring the pressure difference across a deliberately designed and installed flow disturbance. The gas static pressure, density, viscosity, and temperature must be measured or known in addition to the differential pressure. Orifice meters are less accurate than other measurement methods and they do not handle a large range of flow rates. They are however accepted and understood in industrial applications since they are easy to field-service and have no moving parts.
  • Ultrasonic Gas Flow Meters – Ultrasonic flow meters are more complex than meters that are purely mechanical, as they require significant signal processing and computation capabilities. Ultrasonic meters measure the speed of gas movement by measuring the speed at which sound travels in the gaseous medium within the pipe.
  • Coriolis Gas Meters – Coriolis meters can handle a wide range of flow rates and have the unique ability to output mass flow – this gives the highest accuracy of flow measurement currently available for mass flow measurement. Since they measure flowing density, coriolis meters can also infer gas flow rate at flowing conditions.