| 摘要 |
<p>A remote electricity metering system is known in which a central station (LC) communicates with meters (U1-U13) over the mains (10-14), with messages to remote meters being relayed by intermediate meters and the route of a message being determined by the central station. The present system provides alarm signalling whereby the meters can communicate direct with the central station. Each meter can generate a respective combination of alarm frequencies, preferably sequentially and inside the frequency band used for normal messaging, and the local controller monitors the mains for those frequencies. An error detecting and/or correcting code can be used for the alarm frequency combinations. The central stationpolls the meter or meters sending the alarm. The meters are microprocessor-based, with the normal message signals and the alarm frequencies being synthesized from a sequence of digital values by a D/A converter.</p> |
