This invention relates to a dry gas meter of the kind in which flexible diaphragms work back-and-forth in chambers to which the gas being metered is alternately admitted and exhausted. The movements of the diaphragms represent the volume of gas which is passing through the meter, and a mechanism is provided for counting these movements and deriving a measure of the gas volume from the count. Such meters will be termed hereinafter "meters of the kind described".

Commonly these counting mechanisms comprise a series of indicators, one for each decimal digit of a counted multi-digited number, and a mechanical geared drive system connecting the indicators so that they are driven at appropriate relative speeds over respective indices, each marked with digits 0 - 9 over which the indicators move. Problems arise in the reading of a digit when the indicator rests at a position intermediate the marked numbers, and this is particularly found when efforts are made to provide electrical signals relating to the counted number for remote reading of the meter, since the indicator can come to rest at an ambiguous position, trembling between one reading and the next.

The invention provides a dry gas meter of the kind in which flexible diaphragms work back-and-forth in chambers to which the gas being metered is alternately admitted and exhausted, and a counting mechanism is provided for counting these movements and deriving a measure of the gas volume, the counting mechanism comprising a series of indicators each providing one decimal digit of a multi-digited number representing the counted total volume and a mechanical geared drive system connecting the indicators so that they are driven over respective indices each marked with decimal digits 0 - 9, characterized by said . mechanical geared drive system being adapted to drive the indicators through successive steps across the indices, each step carrying the indicator from one digit to the next without an inter¬ mediate step.

Each indicator may comprise a pointer rotating in said steps over a circular dial providing digits 0 - 9 so that it points to each digit in turn.

The pointers may be secured to rotate with index wheels driven in steps through a Geneva mechanism, a known method of transmitting an intermittent drive in which a drive gear has an incomplete ring of teeth. Preferably the index wheels are discs located side-by-side on parallel but spaced apart axes.

According to another aspect, the mechanism for counting the diaphragm movements includes means for reading each digit of the counted number and sending a coded electrical signal representing said digit to a remote reading station.

A specific embodiment of the invention is shown in the accompanying drawings, in which:-

Figure 1 is an exploded perspective view of the main component of a gas meter, Figure 2 is an exploded perspective view of part of the meter of Figure 1,

Figure 3 is an exploded perspective view of the upper end of the gas meter of Figure 1, Figure 4 is an exploded perspective view of an index assembly of Figure 3, and Figure 5 is a section through the index assembly of

Figure 4.

The gas meter comprises two chambers (11) arranged side-by-side, each divided vertically by a flexible diaphragm (13) so that gas being measured may be alternately admitted and exhausted from either side of the diaphragm, causing it to oscillate back-and-forth. As is usual, the oscillations of the diaphragm are counted to provide a measure of the volume of gas which has passed through the meter.

As seen best in Figure 1, the meter body depends on a unitary core (15) which is an aluminium die casting providing structure for the meter casing, inner gas chamber, valve gear container, index housing and gasways, as described hereinafter in more detail. The core comprises a central vertical partition (16) comprising one side of each of the chambers (11), and two angled walls (17) either side of the partition, each forming one dished shape of a chamber. The upper end of the core forms a recess (19) opening to the side which is the

index housing, and an irregular housing (23) [Figure 3] opening to the top which houses valves, valve drive gear, and index drive means.

The two chambers are completed by cast aluminium outer pans (25,26) [Figure 1], each having a diaphragm (13), both secured to the core (15). Each diaphragm has a central disc (27) secured by a flag arm to a flag (28) extending into housing (23) to drive the valve drive gear and index drive means.

The lower end of the core forms a housing (20) which is closed by a cast aluminium lower cover (30) having a central bossed gas inlet (31) which coπmunicates with housing (20). The upper housing (23) is closed byacast aluminium upper cover (33) having a central bossed gas outlet (34\') which comπunicates with an exhaust tube (36) [Figure 3] in housing (23).

The index housing (19), as best seen in Figure 2, houses an index assembly (34) [seen in detail in Figure 4], and has a cover (35) having a viewing plate through which the meter reading can be read. A sealed bush bearing (37) in the rear wall of the housing allows a lay shaft (41) passage to drive an output gear (38) and through it change wheel (39) and index drive gear (40), which operates the index assembly (34) to count the oscillations of the diaphragm.

Adjacent each outer pan (25, 26), the core (15) has an angled face (43, 44) which mates with a similarly angled face (45, 46) on the corresponding outer pan. Gasways (47, 48) connect through openings (50) into the interior of the pans on the outer side of diaphragms (13). On the inner side of the diaphragms (13) the core provides gasways (51), also connected to the interior of the chambers (11).

Gasways (51, 48, 47) all extend up through the core and through a lower wall of the upper housing (23) ending in the same plane. Exhaust tube (36) [Figure 3] is forked to provide a pair of entrances (61) and the tube is mounted so that these lie in the same plane as the entries to gasways (51, 48, 47). A valve grating (60) for each chamber (11) covers the two gasways to either side of the diaphragm and one of the exhaust tube entrances (61). Gasways from housing (20) open into the upper housing (23) so that it is at all times filled with the gas being metered. An oscillating valve cover (62) for each valve grating alternately admits gas from housing. (23) to either side of the diaphragm

and exhausts it from the chambers into exhaust tube (36) and out of outle (34\' ) . Thus the flowing gas is forced to move the diaphragms back-and- forth which are secured to move flag rods (28) . Flag rods (28) drive oscillating top arms (64) which are connected to cranks (65) which rotate a gearbox (66) . Gear (67) driven by the gearbox output connects with output gear (68) which rotates layshaft (41) which in turn drives output gear (38) [Figure 2]. Change wheel (39) is selected to provide a gear ratio which effectively calibrates the individual meter.

Cover drive arms (69) are driven from gears (70) of the gearbox and connected to the valve covers (62) to oscillate them in timed relationship to the diaphragm movements as described above.

Change wheel (39) drives index drive gear (40) at the calibrated rate to rotate a first index wheel (71) in the index assembly (34) [Figure 4]. A counting series of four disc-shaped counting index wheels (72, 73, 74, 75) are mounted in the assembly wall (76) to rotate about parallel, spaced apart axes and interconnected byaseries of pinions (77) which are intermittently driven by the index wheels.

Each index wheel carries on one side a continuous gear (78) [Figure 5] and on the other side an isolated pair of teeth (79). Each pinion (77) carries on one side a drive gear (82) which continuously engages gear (78) of one index wheel and on the other side a transfer gear (83) which is intermittently engaged by teeth (79) of the previous index wheel. Thus each pinion is moved through a known arc once in each rotation of the previous index wheel and this arc is transferred to the succeeding index wheel. Thus each index wheel is driven in steps, not in a continuous movement. The gearing of the pinions and index wheel is selected so that each wheel steps in increments of 1/10 of a revolution. Each succeeding index wheel relates to a higher value digit of the total decimal counted number. Each index wheel (72, 73, 74, 75) is mounted on a shaft which passes through a front wall (80) of the index assembly to mount a pointer (81). Each pointer (81) co-operates with a dial over which it is driven to point to an appropriate decimal index number. As is clear from the above description, each pointer is stationary most of the time, stepping rapidly from one idex number to the next when the appropriate pinion (77) drives the respective index wheel. Thus no

intermediate position need be read, all the pointers pointing directly at an index number.

As best seen in Figures 2, 4 and 5, because the index wheels are discs located virtually side-by-side the whole index assembly is shallow and can be fitted into housing (19) with little or no protrusion from the overall surface of the meter, thus contributing to the small size and neatness of the meter.

According to another embodiment, an electronic reading device is associated with the pointers for transmitting electrical signals representing the reading to a remote station. Since the pointers point unaiπbiguously at a discrete number the means for reading them electrically is much simplified. For instance, discrete electrical contacts may be associated with each digit, with the pointer or index wheel carrying a sliding electrical contact which will unambiguously make contact as the pointer indicates a number.