Communications: electrical – Continuously variable indicating – With meter reading
Patent
1994-12-08
1997-01-14
Hofsass, Jeffery
Communications: electrical
Continuously variable indicating
With meter reading
34087018, 3408703, 34087031, G08C 2300
Patent
active
055944310
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the remote reading of meters and in an important example to the remote reading by public utilities of water or other meters.
There already exist systems for the remote reading of water meters. Typically, each water meter is provided with an encoder capable of deriving a digital encoding of the meter reading. In the case of a water meter having conventional number wheels, the encoder may operate to sense electrically the position of the number wheels. Since each water meter is read relatively infrequently, the encoder means is not normally powered but derives the power necessary for encoding from the remote reader. The encoder may be situated entirely at the meter site or may include an interface connected with the meter but positioned for more straightforward access.
In one known arrangement, the encoder interface and the portable reader are connected by a plug and socket arrangement. In this way it is a simple matter to establish the necessary connections for the supply to the encoder of power and the necessary clock signal, and for transmission of data from the encoder to the reader. Plug and socket connections are regarded as inconvenient, however, and alternative prior proposals operate through inductive coupling. Suitable arrangements of coils in the encoder interface and the portable reader allow for the supply of power and clock information to the encoder and the transmission from the encoder of data. One particular prior proposal (see for example EP 0 131 732) enables the use of a single pair of coils. This has the advantage of significantly reducing the component cost at the encoder interface. In this prior proposal, there is developed a combined power and clock signal which comprises a relatively high frequency periodic signal within a square wave envelope. Thus the power signal comprises a regular succession of high frequency bursts. The encoder is arranged through careful timing no transmit during the gaps between these high frequency bursts. In fact, the transmission from the encoder takes the form of a like-burst of high frequency signal with the presence of such a burst between adjacent bursts of the power signal representing a binary "0" and the absence "1".
An alternative arrangement, disclosed in EP 0 463 893, is intended to operate under both plug and socket and inductive couplings. In the inductive coupling, or so-called "two wire" mode, data is transmitted by varying the current drawn by the meter interface, in synchronism with the interrogating clock signal. Thus, a change in current level every 16 clock cycles is interpreted as a logical "1", and a change in current level every 8 clock cycles as a logical "0".
It is an object of this invention to provide a remote meter reading system which can be implemented with one inductive coupling or other single channel but which does not rely for transmission or detection upon synchronization with the power signal.
Accordingly, the present invention consists in one aspect in a remote meter reading system comprising an encoder for association with a meter and a portable reader, the encoder having power terminal means for connection with a source of electrical power in the reader and adapted when powered to derive a digital encoding of the meter reading for transmission to the reader, characterised in that the encoder comprises impedance switch means serving to vary the input impedance at the power terminal means in representation of the digital encoding to provide a voltage variation detectable at said power source.
Advantageously, the encoder comprises a frequency reference controlling the timing of the impedance switch means.
Preferably, the reader generates a periodic power signal which is inductively coupled with the power terminals of the encoder, the period of said inpedance switch means being longer than the period of the power signal.
Suitably, the switch means comprises a diode connected between the power terminal means and a data line, the diode being selectively reverse biassed in dependence upon the level o
REFERENCES:
patent: 5252967 (1993-10-01), Brennan et al.
Goseltine Robert
Sheppard Frank
ABB Kent PLC
Hill Andrew
Hofsass Jeffery
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