A gas meter with a simple structure for detecting a range from a minute flow rate, such as a gas leak, to the large flow rate of the normal state of use of the gas, while protecting the flow rate sensor from dust and without producing the problem of pressure loss. First, second, and third flow paths (2, 3, 4) for carrying partial flows of a gas to be measured, in accordance with the flow rate, are provided by partitioning, in parallel, the cross-sectional surface of a main flow path (1). A flow rate sensor (5) for flow rate measurement is provided in the first flow path (2) with a small flow path cross-sectional area, and a flow rate sensor (6) for detecting a gas leak is provided in the second flow path (3) with a small flow path cross-sectional area, where a flow baffling filter (15) is provided on one end side or both ends of the first and second flow paths (2, 3), and a contaminant (dust) removing filter (7) is provided on one end side or both ends of the first flow path (2).

A method of determining the volumetric flow rate of a fluid, which determines the volumetric flow rate of said fluid essentially independently of the properties of the fluid, comprises the following steps:

   guiding the volumetric fluid flow to be measured through an essentially linear flow resistor (110);

generating an alternating fluid flow and superimposing the same on the volumetric fluid flow to be measured;

detecting the pressure drop across the flow resistor (110);

determining the steady component and the alternating component of the pressure drop detected;

determining a quantity (FV) representative of a fluid property of the fluid on the basis of the alternating component which has been determined;

and

calculating the volumetric flow rate on the basis of the steady component which has been determined as well as on the basis of the quantity (FV) representative of the fluid property.

A fluid flow sensing apparatus for measuring very low fluid flows comprising a fluid mass flow sensor for measuring the mass flow rate of a fluid from a temperature differential between predefined points within the sensor; a fluid flow channeling element for accepting the fluid at an input temperature and pressure and directing the fluid across the sensor, and wherein the input temperature and pressure about the sensor is maintained; and a fluid flow dampening element for providing an average fluid flow to the sensor.

A fluid flow sensing apparatus for measuring very low fluid flows comprising a fluid mass flow sensor for measuring the mass flow rate of a fluid from a temperature differential between predefined points within the sensor; a fluid flow channeling element for accepting the fluid at an input temperature and pressure and directing the fluid across the sensor, and wherein the input temperature and pressure about the sensor is maintained; and a fluid flow dampening element for providing an average fluid flow to the sensor.