Patent GB-1425182-A (GB)
Title: Automatic meter-reading system
IPC: G01D4/00
Filed: 1973-01-26
Abstract: 1425182 Selective signalling MITSUBISHI DENKI KK 26 Jan 1973 [11 July 1972 14 July 1972 (2) 29 July 1972 3 Aug 1972] 4183/73 Heading G4H [Also in Divisions H3 and H4]  In an automatic meter-reading system, measured information is encoded in terms of resistance values which are scanned by a scanner driven from a central station to communicate the values to the central station. A programmed central processor in the central station controls an automatic dialling unit to select a subscriber's line-pair in an automatic telephone switching system 6, Fig. 6. Resistances are measured by their effect on line current passing through a resistor 22 in the central station across which an A/D converter is connected, the A/D converter feeding the central processor for calculations of actual resistance values. Line and ground insulation resistances and contact failure of the telephone link are tested by applying various D.C. voltages to the line-pair and using the A/D converter. A D.C. voltage applied to the line-pair then turns on a thyristor 32 at the subscriber's location, a timer circuit 33, 36-40 connected to the thyristor preventing erroneous turn-on, e.g. during dialling. A relay K is then turned on at the subscriber's location to advance a stepping motor 42 controlling switches 43, and to insert a diode 31 into the line-pair to prevent ringing in the subscriber's telephone handset 41. The central station reverses the D.C. on the line-pair repeatedly to drive the stepping motor 42 which thus connects various resistors (not all shown) 48-50, 11&c. into the line-pair in turn. The resistors are: a standard resistance, a resistance corresponding to the subscriber's telephone number (for a check comparison of the central station), three resistances identifying electric power, gas and water meters respectively, each of the latter resistances being accompanied by four resistances variably set with the thousands, hundreds, tens and units digits of the meter reading respectively. The resistances may be scanned by the stepping motor a plurality of times, for checking purposes. The relay K also controls equipment 13, the state of which is signalled using another resistor. If the subscriber lifts his receiver, the relay K is shorted, and the subscriber's call takes precedence. In a twoparty line system, the two units 9 are crosscoupled to the line-pair and each has an extra relay to permit actuation of the respective thyristor, the polarity on the line pair selecting between the two subscribers: Two or more subscribers may be connected to the line-pair (without cross-coupling) the "extra relay " referred to being actuated via a filter by a respective frequency. An alternative modification of Fig. 6 has a plurality of units 9 connected in series in the same subscriber's linepair, each unit having a further relay so that the units 9 are enabled in turn (only the first unit 9 having the components 32-41). Fig. 11 shows the reading of telephone subscribers' meters at a central telephone exchange office, the figure showing the central processor 1, automatic dialling unit 2, telephone switching system 6, A/D converter 4, and a two-party line-pair L1, L2. There is a unit 17 for each subscriber with resistors 18 variably controlled by the meter reading and a resistor 59 corresponding to the subscriber's number (for checking purposes). A standard resistor 57 and a resistor 58 for subscribers' meter reading (the latter for checking purposes) are provided in common. One of the unit 17 is selected by the output of switching system 6, and a stepping motor 66 closes switches 67 in turn so that A/D converter 4 responds to the various resistance values in turn, the resistances being calculated at 1 in accordance with the A/D converter outputs.