A
gas meter is used to
measureIn science, measurement is the process of obtaining the magnitude of a quantity, such as length or mass, relative to a unit of measurement, such as a meter or a kilogram...
the volume of
fuel gasFuel gas can refer to any of several gases burned to produce thermal energy.Natural gas is the most common fuel gas, but others include:* Town gas* Syngas* Mond gas* Propane* Butane* Regasified liquified petroleum gas* Wood gas* Producer gas...
es such as
natural gasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills...
and
propanePropane is a three-carbon alkane, normally a gas, but compressible to a transportable liquid. It is derived from other petroleum products during oil or natural gas processing...
. Gas meters are used at residential, commercial, and industrial buildings that consume fuel gas supplied by a gas
utilityA public utility is an organization that maintains the infrastructure for a public service . Public utilities are subject to forms of public control and regulation ranging from local community-based groups to state-wide government monopolies...
. 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.
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 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 chambers formed by movable
diaphragmIn mechanics, a diaphragm is a sheet of a semi-flexible material anchored at its periphery and most often round in shape. It serves either as a barrier between two chambers, moving slightly up into one chamber or down into the other depending on differences in pressure, or as a device that...
s. With the gas flow directed by internal
valveA valve is a device that regulates the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category....
s, the chambers alternately fill and expel gas, producing a near continuous flow through the meter. As the diaphragms expand and contract, levers connected to
crank-Science:* Crank conjecture, a term coined by Freeman Dyson to explain congruence patterns in integer partitions* Crank , someone who holds pseudoscientific theories no matter what evidence is presented to the contrary.-Mechanism:...
s convert the linear motion of the diaphragms into rotary motion of a crank shaft which serves as the
primary flow elementA primary flow element is the element of a flow meter that serves to indicate the quantity or velocity of flow.For example, in the case of an orifice flow meter, the differential pressure across the orifice plate is the primary flow element...
. This shaft can drive an odometer-like
counterIn digital logic and computing, a counter is a device which stores the number of times a particular event or process has occurred, often in relationship to a clock signal...
mechanism or it can produce electrical pulses for a
flow computerA flow computer is an electronic computational device which implements the required algorithms to turn the raw data received from flow meters to which it is connected into volumes at base conditions....
.
Diaphragm gas meters are
positive displacementA positive displacement meter is a type of flow meter that requires the fluid being measured to mechanically displace components in the meter in order for any fluid flow to occur. Positive displacement flowmeters make volumetric flow measurements taking finite increments or volumes of the fluid...
meters.
Major manufacturers of diaphragm meters in the US include Actaris, Dresser Wayne Pignone, Elster American Meter, and Sensus.
Rotary 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. With each turn, they move a specific quantity of gas through the meter. The operating principle is similar to that of a Roots blower. The rotational movement of the crank shaft serves as a
primary flow elementA primary flow element is the element of a flow meter that serves to indicate the quantity or velocity of flow.For example, in the case of an orifice flow meter, the differential pressure across the orifice plate is the primary flow element...
and may produce electrical pulses for a
flow computerA flow computer is an electronic computational device which implements the required algorithms to turn the raw data received from flow meters to which it is connected into volumes at base conditions....
or may drive an odometer-like
counterIn digital logic and computing, a counter is a device which stores the number of times a particular event or process has occurred, often in relationship to a clock signal...
.
Major manufactures include Elster American Meter, Dresser Roots, and Romet Limited.
Turbine 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 lower flow rates.
Major Manufacturers include: Elster American Meter, Elster Instromet, and Sensus
Orifice 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'Turndown ratio' is a flow measurement term that indicates the range a specific flow meter, or meter type, is able to measure with acceptable accuracy. It is also known as rangeability. It is important when choosing a flow meter technology for a specific application...
. They are however well accepted and understood in industrial applications since they are easy to field-service and have no moving parts.
Ultrasonic flow meters
Ultrasonic flow meters are much 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. AGA Report No. 9 covers the proper usage and installation of these meters, and it specifies a standardised speed-of-sound calculation which predicts the speed of sound in a gas with a known pressure, temperature and
gas compositionGas composition: any gas can be characterised by listing the pure substances it contains, and stating for each substance its proportion of the gas mixture's molecule count.To give a familiar example, air has a composition of:...
.
The most elaborate types of ultrasonic flow meters average speed of sound over a total of four paths in the pipe. The length of each path is precisely measured in the factory. Each path consists of an ultrasonic transducer at one end and a sensor at the other. The meter creates a 'ping' with the transducer and measures the time elapsed before the sensor receives the sonic pulse. Two of these paths point upstream so that the sum of the times of flight of the sonic pulses can be divided by the sum of the flight lengths to provide an average speed of sound in the upstream direction. This speed differs by the speed of sound in the gas by the velocity at which the gas is moving in the pipe. The other two paths are identical except that the sound pulses travel downstream. The meter then halves the difference between the upstream and downstream speeds to calculate the velocity of gas flow.
Ultrasonic meters are high-cost and must have no liquids present at all in the measured gas, so they are primarily used in high-flow, high-pressure applications such as utility pipeline meter stations, where the gas is always dry and lean, and where small proportional inaccuracies are intolerable due to the large amount of money at stake. The
turndown ratio'Turndown ratio' is a flow measurement term that indicates the range a specific flow meter, or meter type, is able to measure with acceptable accuracy. It is also known as rangeability. It is important when choosing a flow meter technology for a specific application...
of an ultrasonic meter is probably the largest of any natural gas meter type, and the accuracy and
rangeability'Turndown ratio' is a flow measurement term that indicates the range a specific flow meter, or meter type, is able to measure with acceptable accuracy. It is also known as rangeability. It is important when choosing a flow meter technology for a specific application...
of a high-quality ultrasonic meter is actually greater than that of the turbine meters against which they are proven.
Inexpensive varieties of ultrasonic meters are available as clamp-on flow meters, which can be used to measure flow in any diameter of pipe without intrusive modification. Such devices are based on two types of technology: (1) time of flight or transit time; and (2) cross correlation. Both technologies involve transducers that are simply clamped on to the pipe and programmed with the pipe size and schedule and can be used to calculate flow. Such meters can be used to measure almost any dry gas including natural gas, nitrogen, compressed air and also steam. Clamp-on meters are available for measuring liquid flow as well.
Coriolis meters
A coriolis meter is a pipe with a laterally displaced section that is excited to vibrate at its resonant frequency. Coriolis meters are often used with liquids but can be used with natural gas as well. When the fluid within the displaced section is at rest, both the upstream and downstream elbows of the laterally displaced section will vibrate in phase with each other. The frequency of this vibration is determined by the overall density of the pipe (including its contents). This allows the meter to measure the flowing density of the gas in real time. Once the gas begins to flow, however, the
coriolis effectIn physics, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame.Newton's laws of motion govern the motion of an object in an inertial frame of reference. When transforming Newton's laws to a rotating frame of reference, the Coriolis...
comes into play. This effect implies a relationship between the phase difference in the vibration of the upstream and downstream pipe elbows and the mass flow rate of the fluid contained by the pipe.
Again, owing to the amount of inference, analog control and calculation intrinsic to a coriolis meter, the meter is not complete with just its physical components. There are actuation, sensing, electronic and computational elements that must be present for the meter to function.
Coriolis meters can handle a wide range of flow rates and have the unique ability to output mass flow. Since they measure flowing density, coriolis meters can also infer gas flow rate at flowing conditions.
AGA Report No. 11 provides guidelines for obtaining good results when measuring natural gas with a coriolis meter.
Heating value
The volume of gas flow provide by a gas meter is just that, a reading of volume. Gas volume does not take into account the quality of the gas, the amount of heat available when burned. Utility customers are billed according to the heat available in the gas. The quality of the gas is measured and adjust for in each billing cycle. This is known by several names as the calorific value, heating value, or
thermThe therm is a non-SI unit of heat energy equal to 100,000 British thermal units . It is approximately the energy equivalent of burning 100 cubic feet of natural gas....
value.
The calorific value of
natural gasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills...
can be obtained using a process gas chromatograph, which measures the amount of each constituent of the gas, namely:
- methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean...
- ethane
Ethane is a chemical compound with chemical formula C
2H
6. It is the only two-carbon alkane that is an aliphatic hydrocarbon. At standard temperature and pressure, ethane is a colorless, odorless gas....
- carbon dioxide
Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
- water
Water is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
Additionally, to convert from volume to thermal energy, the
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
and
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
of the gas must be taken into consideration. Pressure is generally not a problem; the meter is simply installed immediately downstream of a
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
regulatorA pressure regulator is a valve that automatically cuts off the flow of a liquid or gas at a certain pressure. Regulators are used to allow high-pressure fluid supply lines or tanks to be reduced to safe and/or usable pressures for various applications....
and is calibrated to read accurately at that pressure. Pressure compensation then occurs in the utility's billing system. Varying temperature cannot be handled as easily, but some meters are designed with built-in temperature compensation to keep them reasonably accurate over their designed temperature range. Others are corrected for temperature electronically.
Indicating devices
Any type of gas meter can be obtained with a wide variety of indicators. The most common are indicators that use multiple clock hands (pointer style) or digital readouts similar to an
odometerAn odometer indicates distance traveled by a car or other vehicle. The device may be electronic, mechanical, or a combination of the two. The word derives from the Greek words ""hodós", meaning "path" or "way", and "métron", "measure".-Description:In the early autos a top reading of 99,999 was...
, but remote readouts of various types are also becoming popular — see
automatic meter readingAutomatic meter reading, or AMR, is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices and transferring that data to a central database for billing, troubleshooting, and analyzing.This advance mainly saves utility...
and
smart meterA smart meter is an advanced meter that identifies consumption in more detail than a conventional meter; and optionally, but generally, communicates that information via some network back to the local utility for monitoring and billing purposes .-Overview:Smart meter often refers to an electrical...
.
Remote Readouts
Remote reading is becoming popular for gas meters. It is often done through an electronic pulse output mounted on the meter. There are different styles available but most common is a contact closure switch.
Flow measurement calculations
Turbine, rotary and diaphragm meters can be compensated using a calculation specified in AGA Report No. 7. This standardised calculation compensates the quantity of volume as measured to quantity of volume at a set of
base conditionsBase conditions consist of a specified absolute pressure and temperature. To ensure accuracy, it is important to refer to base conditions when measuring the volume of a sample of liquid or gas. This applies to both static measurement and flow measurement....
. The AGA 7 calculation itself is a simple ratio and is, in essence, a density correction approach to translating the volume or rate of gas at
flowing conditionsIn fluid measurement, the fluid's flow conditions refer to quantities like temperature and static pressure of the metered substance. The flowing conditions are required data in order to calculate the density of the fluid at flowing conditions...
to a volume or rate at
base conditionsBase conditions consist of a specified absolute pressure and temperature. To ensure accuracy, it is important to refer to base conditions when measuring the volume of a sample of liquid or gas. This applies to both static measurement and flow measurement....
.
Orifice meters are a very commonly used type of meter, and because of their widespread use, the characteristics of gas flow through an orifice meter have been closely studied. AGA Report No. 3 deals with a broad range of issues relating to orifice metering of natural gas, and it specifies an algorithm for calculating natural gas flow rates based on the differential pressure, static pressure and temperature of a gas with a known composition.
These calculations depend in part on the
ideal gas lawThe Ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behaviour of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...
and also require a gas compressibility calculation in order to account for the fact that real gases are not ideal. A very commonly used gas compressibility calculation is AGA Report No. 8, detail characterization.
See also
- Gas meter prover
A gas meter prover is a device which verifies the accuracy of a gas meter. Provers are typically used in gas meter repair facilities, municipal gas meter shops, and public works shops. Provers work by comparing a known volume of air across a meter with the gas meter's index or register. A series...
- Automatic Meter Reading
Automatic meter reading, or AMR, is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices and transferring that data to a central database for billing, troubleshooting, and analyzing.This advance mainly saves utility...
- Utility submeter
Utility Submetering is the implementation of a system that allows a landlord, property management firm, condominium association, homeowners association, or other multi-tenant property to bill tenants for individual measured utility usage...
- Water meter
A water meter is a device used to measure the volume of water usage. This article provides an overview of technical aspects of water meters. The worldwide prevalence of metering as well as its economic benefits and costs are covered in the separate article on water metering.In many developed...
- Heat meter
- Electricity meter
An electric meter or energy meter is a device that measures the amount of electrical energy supplied to or produced by a residence, business or machine....
- Flow measurement
Flow measurement is the quantification of bulk fluid movement. It can be measured in a variety of ways.- Units of measurement :Both gas and liquid flow can be measured in volumetric or mass flow rates, such as litres per second or kilograms per second. These measurements can be converted between...
- Meter-Bus
M-Bus is a European standard for the remote reading of gas or electricity meters. M-Bus is also usable for other types of consumption meters. The M-Bus interface is made for communication on two wire, making it very cost effective...
- Thermal mass flow meter
-Introduction:There are two types of thermal mass flow meters in industry. Industrial thermal mass flow meters, also known as thermal dispersion or immersible mass flow meters comprise a family of instruments for the measurement of the total mass flow rate of a fluid, primarily gases, flowing...