Gas density meter and method

A method for determining a ratio ##EQU70## of a density .rho..sub.f of a pipeline gas in a pipeline at a flowing temperature and pressure compared to a density .rho..sub.b of the pipeline gas at a base temperature and pressure, the method comprising:

• flowing sample gas tapped from the pipeline to a first chamber of fixed volume, the sample gas being maintained at substantially the same temperature as the pipeline gas flowing temperature when contained in the first chamber;
• measuring the pressure of the sample gas in the first chamber;
• measuring the temperature of the sample gas in the first chamber which is substantially the same as the pipeline gas flowing temperature;
• stopping the flow of sample gas to the first chamber when the pressure in the first chamber reaches the pipeline gas flow pressure;
• flowing sample gas from the first chamber at a substantially constant mass flowrate;
• determining the time rate of change of the pressure in the first chamber;
• and
• deriving the ratio ##EQU71## from the time rate of change of pressure in the first chamber and the flowing temperature and pressure.

A method for determining a flowing condition density .rho..sub.f of a pipeline gas flowing through a pipeline at a flowing temperature and pressure, the method comprising:

• measuring a base condition density .rho..sub.b of the pipeline gas;
• flowing sample gas tapped from the pipeline to a first chamber of fixed volume until the pressure in the first chamber reaches the pipeline gas flowing pressure, the sample gas being maintained at substantially the same temperature as the pipeline gas flowing temperature when contained in the first chamber;
• measuring the pressure of the sample gas in the first chamber;
• measuring the temperature of the sample gas in the first chamber which is substantially the same as the pipeline gas flow temperature;
• stopping the flow of sample gas to the first chamber and flowing the sample gas from the first chamber at a substantially constant mass flowrate;
• measuring the time rate of change of the pressure in the first chamber,
• deriving the flowing condition density .rho..sub.f of the pipeline gas from the flowing temperature and pressure, the time rate of change of pressure in the first chamber, and the base condition density .rho..sub.b.

A flowmeter that determines a base condition volumetric flow rate Q.sub.b of a gas flowing through a pipeline which corresponds to a volumetric flow rate at a base temperature and pressure comprising:

• a volumetric flowmeter for measuring a flowing condition volumetric flow rate of the pipeline gas Q.sub.f flowing through the pipeline at a flowing temperature and pressure;
• means for tapping sample gas from the pipeline;
• a first chamber of fixed volume for receiving sample gas tapped from the pipeline, the sample gas being maintained at substantially the same temperature as the pipeline gas flowing temperature when contained in the first chamber;
• a first pressure sensor for measuring the pressure of the sample gas in the first chamber;
• a first temperature sensor for measuring the temperature of the sample gas in the first chamber;
• a first valve for controlling the flow of sample gas to the first chamber;
• a flow restrictor located downstream of the first chamber through which sample gas flowing from the first chamber flows;
• a pressure regulator located downstream of the first chamber and upstream of the flow restrictor for reducing the pressure of sample gas flowing from the first chamber before it flows to the flow restrictor so that flow from the first chamber through the flow restrictor is maintained at a substantially constant rate;
• and
• a controller for receiving signals from the first pressure sensor and the temperature sensor, for deriving a ratio ##EQU72## of a density .rho..sub.f of the pipeline gas at the flowing temperature and pressure compared to a density .rho..sub.b of the pipeline gas at the base temperature and pressure, and for deriving the base condition volumetric flow rate of the pipeline gas Q.sub.b by multiplying the flowing condition volumetric flow rate of the pipeline gas Q.sub.f by the ratio ##EQU73##