Mains signalling systems

Details Mains signalling systems Mains signalling systems

1996-05-30

1998-03-24

Hofsass, Jeffery

Communications: electrical

Continuously variable indicating

With meter reading

34087009, 340538, 34031006, G08C 1506

Patent

active

057317658

DESCRIPTION:

BRIEF SUMMARY
The present invention relates primarily to mains signalling systems, though it is also applicable to other systems having similar characteristics. (The term "mains" applies primarily to the final consumer voltage portions of an electricity supply network, though the signalling can also extend over the higher voltage distribution parts of the network.) Such signalling is termed mains, mainsborne, or power line carrier (PLC) signalling.


REMOTE METERING

A major application of mains signalling is remote meter reading, operated by electricity generating and distribution companies (electricity utilities). The term "remote meter reading" refers to what is normally the major function of such systems, but they may also be concerned more generally with load and system control. Also, while they will usually be concerned primarily with electricity meters, gas and other meters can in principle be coupled to the mains for this purpose (preferably through electricity meters).
A typical simple remote meter reading system will have a central station or local controller (which can conveniently be located at a distribution transformer) which communicates over the mains with the meters (meter stations) of the various premises (largely household or domestic and small commercial) on the mains.
Such systems normally use some form of frequency modulation (in the broad sense). There is in fact an international standard now for such signalling, using frequencies in the general region of 3-150 kHz. (The standard is CENELEC EN50065.1, which specifies that frequencies in the band 3-148.5 kHz are available for signalling on low voltage electrical installations. This bandwidth is divided into several smaller bands with various uses and permissions associated with them; for example, the 9-95 kHz band is reserved for electricity suppliers and their licencees.)
Any suitable form of signalling can be chosen within that standard. One convenient form is FSK (frequency shift keying), in which information is transmitted by switching between two predetermined frequencies. This requires suitable signal generators and detectors.
The meters will normally be microprocessor-based. With such a meter, a convenient technique for signal generation is to use a digital-to-analog converter which is driven by a sequence of values defining a sine wave, obtained e.g. by reading them from a memory at a suitable rate; the signal frequency can be controlled by varying the reading rate. Good control of the waveform can readily be achieved, using say 8-bit words, say 128 or 256 samples defining a quarter-wave, and division down from say a 10 MHz clock. Signal detection requires detection of the two signalling frequencies. This can be achieved by providing fixed tuned circuits; alternatively, integrated circuits are available which are designed for such frequency signal detection.
Mains signalling systems have two major problems: noise and attenuation.
Mains noise arises from loads being switched on and off and the inherent characteristics of certain types of loads. The noise problem can generally be overcome by a variety of known techniques, such as error detection and correction techniques, requiring acknowledgement of reception, and repetition of lost messages. (Some of these techniques also deal with problems of message collision.)
Dissipation or attenuation at the preferred signal frequencies is significant; it is dependent on the particular operating conditions of the mains network and varies according for example to the loading of the network. The attenuation will often be irregular; there may for example be "dead spots", due e.g. to signal reflections, close to the signal source while communication to more distant locations is still reasonably reliable.
A system which largely overcomes these problems has been proposed in our earlier patent application no. PCT/GB94/01391, WO 95/01030. In that system, which we will for convenience call the "standard system", substantially all meters have a repeater function. The present system is a broadly a development of

REFERENCES:
patent: 4337466 (1982-06-01), Spahn
patent: 4446458 (1984-05-01), Cook
patent: 4446462 (1984-05-01), Ouellette et al.
patent: 4804957 (1989-02-01), Selph et al.

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