How do gas meters measure how much gas you use if gas can be compressed? (unlike water)


How do gas meters measure how much gas you use if gas can be compressed? (unlike water)

In: Engineering

Because the gas is supplied at a set pressure.

There’s a flow meter that reads the amount of gas that’s gone through it.

So given a set specific pressure and a reading of how much has gone through it’s very easy to know just how much gas has been used.

To measure compressed gas flow rate you need to know the velocity of the gas, the density at a reference temperature, current temperature and current pressure.

In a residential application; density, pressure, and temperature are fairly constant, so all you need is a way to measure velocity. This is the sensing element in a flow meter, usually either a spinning turbine or a positive displacement type.

There are other more complicated ways to design a flow meter that you can easily google but these are the basics.

Source: am an industrial instrumentation tech

From Wikipedia

“Diaphragm/bellows meters

A diaphragm type gas meter.

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 diaphragms. With the gas flow directed by internal valves, the chambers alternately fill and expel gas, producing a nearly 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 flow computer.
Diaphragm gas meters are positive displacement meters.”

The positive displacement chambers combined with knowing the pressure provides a reliable reading for the low flow rates for home gas meters.

1) Gas is supplied at a particular pressure, and how much the gas is compressed at that pressure is fairly easy to calculate. Thus, if you know exactly how much the gas is being compressed, you know how much gas is flowing.

2) Gas is actually easy to meter and control if you have a pressure change on either side of your meter; as the gas expands from one pressure to another (say, 500 psi to 50 psi), it’ll also have a temperature change. The precise amount of the temperature change corresponds *directly* to how much gas is actually flowing; all you need to know is what mixture of species are actually in the gas. Thus, if you know what the gas is made of, and you can measure the temperature and pressure of the gas on either side of a regulator, you know precisely how much gas is flowing.

The gas bills here show the “calorific value”, which changes through the year, due to expansion in summer and compression in winter.

The simplest systems measure the pressure drop across an orifice for which flow can be calculated for an assumed or measured temperature and composition.