AMR MERCURY-PLC is designed for remote collection of power, water, gas and heat consumption data. The system can be used whenever there is a need for reliable remote reading of slowly-changing data. The system’s distinct feature is its low price and extremely high tolerance to the noise, signal attenuation and distortion which often take place in realworld AC distribution networks. The main field of application is in urban, high density, built-up areas for multistorey buildings.
The system consists of a number of meters with PLC modems (up to 3000 subscriber devices) and one concentrator, and provides reliable data collection at signal attenuation on the line of up to -60dB and signal/noise ratio up to -20dB (not simultaneously).
To transmit data to/from the devices, wide-band and noise-like signals are used in a frequency range from 20 to 95kHz (CENELEC-A) with amplitudes around 1.5V.
Unlike the majority of data collection systems designed as peer-to-peer networks of identical modems, the Mercury-PLC system represents an asymmetrical solution. The main function of the system’s central unit – the concentrator – is to manage subscriber modem time synchronisation, in order to ensure their signals diversify in time.
The technical solution is secured by two international patents.
LOW-COST PLC MODEM FOR DIGITAL E-METER
The main feature of the PLC modem used in the system is extremely low power consumption, as well as exceptional tolerance to noise and signal attenuation on the line. Device dimensions are 40x60x22mm (including its own power supply source).
The modem is built with an inexpensive micropower controller (MSP430F155) from Texas Instruments, and uses a wideband OFDM type of modulation for transmitting data to the concentrator. It is a complex modulation type, but the modem’s microcontroller simply ‘replays’ one of the two earlier recorded signal tables.
In receive mode the microcontroller implements a simple narrow-band digital PSK receiver algorithm with program switching of reception frequency.
PLC DATA CONCENTRATOR
The single phase PLC data concentrator is built with microcontroller-type DSP TMS320LF2407A, also from Texas Instruments, with 40 MHz core frequency. It performs the task of power line signal digitising and processing, and includes complex 256-radix FFT and OFDM spectrum restoration. If the power line noise is too high (making the immediate recovery of subscriber modem data signal impossible) the concentrator's DSP starts an original signal averaging procedure in order to improve the signal-to-noise ratio.
To simplify the bit synchronisation task, the zero crossing points of the mains voltage is used for system timing events.
Over the last year about 80 pilot projects have been installed in various regions of Russia and CIS countries, with a total of about 50,000 points being read using this system. These installations include locations with a variety of noise level and signal attenuation rates. The pilots have confirmed the technical viability of using the system described above.
High reliability data transmission in conditions of high noise level (data transmission was sometimes carried out over distances up to 2000 metres without signal retransmission) have been conclusively confirmed. The Mercury-PLC AMR system fundamentally changes the approach of controlling the relationship between utility and customer, and allows the move from traditional manual, non flexible, bureaucratic control to flexible, simple and – in the long term – individually tailored services for each customer.