Gas Metering

Abstract

A gas meter comprises a conduit for passage of a gas flow and an ionizer to ionize the gas flow. A modulating electrode structure downstream of the ionizer modulates the ion distribution in the ionized gas flow. A first and a second electrode structure downstream of the modulating electrode structure detect the ion distribution in the ionized gas flow. The modulating electrode structure and the detecting electrode structure can generate an electrical field parallel to the direction of the gas flow. The modulating electrode structure and the detecting electrode structures can each have apertures defined therein for passage of the gas flow. The modulating electrode structure can capture ions of one polarity to generate an ionized gas flow comprising a majority of ions of the opposite polarity. Movement of the ionized gas flow generates a current indicative of the ion distribution between the electrode and the charge source.

1 - 28 . (canceled) 
     
     
         29 . A gas meter comprising:
 a conduit for passage of a gas flow, an ioniser arranged to ionise the gas flow in the conduit, a modulating electrode structure downstream of the ioniser arranged for modulating the ion distribution in the ionised gas flow, and   at least a first detecting electrode structure downstream of the modulating electrode structure arranged for detecting the modulated ion distribution in the ionised gas flow,   wherein the modulating electrode structure comprises an upstream electrode and a downstream electrode, and a respective modulating potential is applied to each electrode to modulate the ion distribution in the ionised gas flow,   wherein the modulating potential applied to the downstream electrode is of an opposite polarity to the modulating potential applied to the upstream electrode and of a magnitude selected such that, downstream of the modulating electrode structure, the electric field due to the upstream electrode is cancelled by the electric field due to the downstream electrode.   
     
     
         30 . A gas meter as claimed in  claim 29 , wherein the modulating electrode structure is arranged to capture ions of one polarity, whereby to generate an ionised gas flow comprising a majority of ions of the opposite polarity. 
     
     
         31 . A gas meter as claimed in  claim 30 , wherein at least the first detecting electrode structure comprises at least one electrode connected to a source of charge, whereby movement of the ionised gas flow having a majority of ions of one polarity relative to the at least one electrode causes a redistribution of charge in the at least one electrode, which generates a current indicative of the ion distribution between the at least one electrode and the charge source. 
     
     
         32 . A gas meter according to  claim 29 , wherein the modulating electrode structure is configured to generate an electrical field having at least a substantial component parallel to a direction of the gas flow. 
     
     
         33 . A gas meter according to  claim 29 , wherein at least the first detecting electrode structure is configured to generate an electrical field having at least a substantial component parallel to a direction of the gas flow. 
     
     
         34 . A gas meter according to  claim 29 , wherein the modulating electrode structure comprises a pair of opposed substantially planar electrodes arranged substantially perpendicularly to a direction of the gas flow. 
     
     
         35 . A gas meter according to  claim 29 , wherein at least the first detecting electrode structure comprises a pair of opposed substantially planar electrodes arranged substantially perpendicularly to a direction of the gas flow. 
     
     
         36 . A gas meter according to  claim 29 , wherein the electrodes are spaced in a direction of the gas flow. 
     
     
         37 . A gas meter according to  claim 29 , wherein the electrodes each have a plurality of apertures defined therein for passage of the gas flow through the plurality of apertures. 
     
     
         38 . A gas meter according to  claim 29 , wherein at least one of the modulating electrode structure and at least the first detecting electrode structure comprises a pair of electrodes arranged transversely to a direction of gas flow and having a plurality of apertures defined therein for passage of the gas flow through the plurality of apertures,
 wherein the apertures in one electrode of the pair are offset in a direction transverse to the direction of gas flow relative to the apertures in the other electrode of the pair.   
     
     
         39 . A gas meter according to  claim 38 , wherein the offset between the apertures of respective electrodes of the pair is substantially equal to half of a spacing between adjacent apertures of one of the electrodes. 
     
     
         40 . A gas meter as claimed in  claim 29 , wherein at least one of the electrodes is in the form of a mesh. 
     
     
         41 . A gas meter according to  claim 29 , further comprising a second detecting electrode structure downstream of the first detecting electrode structure, wherein each of the first and second detecting electrode structures are arranged for detecting the modulated ion distribution in the ionised gas flow. 
     
     
         42 . A gas meter as claimed in  claim 41 , wherein the second detecting electrode structure comprises a pair of spaced electrodes, and an electric field is applied between the electrodes to capture ions from the ionised gas flow and generate a current indicative of an ion distribution in the ionised gas flow. 
     
     
         43 . A gas meter according to  claim 29 , wherein a modulating voltage applied to the modulating electrode structure is at a frequency of less than 10 Hz. 
     
     
         44 . A gas meter according to  claim 29 , wherein a modulating voltage applied to the modulating electrode structure is less than 10 volts alternating current (AC). 
     
     
         45 . A gas meter according to  claim 29 , wherein the ioniser comprises a radioactive source. 
     
     
         46 . A gas meter according to  claim 29 , wherein the gas meter is battery powered.