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| Automatic
Meter Reading (AMR) System |
| Archnet Automatic Meter
Reading (AMR) System Overview: |
The remote Automatic Meter
Reading (AMR) System is a host driven, multi-level network system
consisting of a Host Central Station (HCS), Data Concentrator Units
(DCU) and Meter Interfacing Units (MIU), with built-in flexibility
and expandability. Each HCS, while working independently, can also
be integrated with an existing corporate information management
system through software interface. With additional hardware and
software support, the HCS can function as a workstation in an
existing Local Area Network (LAN) and becomes a member of the entire
system, or several HCS can be connected together to form a network
of their own.
Archnet Automatic Meter Reading (AMR) system can be connected
to any Electricity, Gas, Water and flow Meters with pulse output for
Meter Readings. |
| Automatic Meter
Reading (AMR) System Block Diagram: |
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The
DCU and all the MIUs and meters connected to it can be considered as
a sub-system of the HCS. The sub-system is set up with a DCU
monitoring the low voltage power zone downstream of a Distribution
Transformer. The DCU can be viewed as the front end of the
sub-system, collecting meter readings from all the MIUs connected to
it through the low voltage power line carrier (PLC) and
communicating with the HCS through the communication channel. There
are two types of MIUs, a single-channel type connected to a single
meter only, and a multi-channel type, which can be connected up to
16 meters. In projects where meters are scattered around in an open
area, single-channel MIUs are usually used for individual meters.
But for projects where meters are grouped together in a meter room
or cabinet, Multi-channel Meter Interface Units (MMIU) are more cost
effective.
There
are basically two stages of communication in the system, namely,
that between the MIUs and the DCU, and that between the DCUs and the
HCS. The communication channel or medium used between MIU and DCU is
the Power Line; and the channel used between DCU and HCS can be the
Public Switched Telephone Network (PSTN), GSM network, radio
network, or directly with handheld terminals and notebook computers
with a standard RS-232 interface or through a modem. |
| Operating Principle: |
The
communication device for the PLC communication system is a built-in
Power Line Modem (PLM), which transmits and receives data over the
power line. Both the MIU and the DCU contain the PLM device. The
binary data stream is keyed onto a carrier signal by means of the
Frequency Shift Keying (FSK) technique. The central frequency is
shifted +0.3KHz to represent 1 or 0 of the binary data stream. This
signal is then coupled onto the power line by the PLM. At the
receiving end, an identical PLM will detect the signal and convert
it back to a binary data stream. The PLMs operate in a Half Duplex,
two-way, Time Division Multiplex communication mode. Two-way
communication between DCU and MIU is essential in establishing a
proper communication channel, for system synchronization and status
reporting.
In
AMRS, transmission speed is not a great concern but reliability is
important. The data rate of the PLC channel is set at 600 bps, to
ensure communication over a longer distance and reduced transmission
error. Every MIU is also equipped with repeater function. If
required, the DCU can designate any MIU in the sub-system as a
repeater to enhance communication with a particular MIU. With the
sensitive signal detection and sophisticated digital filtering
technique, this PLC communication is highly immune to electrical
noise and interference. |
| PLC Schematics: |
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| Signal, Data and
Information Flow: |
The
MIU is an intelligent device, which can collect, process, and record
power consumption data from the electric meter. It picks up the
pulse output of the meter and converts the measurement of the meter
into a digital format suitable for data processing. Thus it is
possible to monitor the electrical load in real time. The MIU saves
the data collected in non-volatile memory, and all data and settings
are protected against power failure. It will automatically resume
normal operation when power returns after a power failure. After
receiving a Multi-rate Tariff command and loading the time-of-use
table from the DCU, the MIU will process energy consumption data
according to pre-set time intervals. It will update the peak values
and their time of occurrence at each tariff rate providing real time
information of electrical consumption for the information management
system.
Data stored in the MIU are
transmitted to the DCU via the power line through the built-in Power
Line Modems (PLM). Communication is initiated by the DCU, which
polls the MIU by calling its address. Data received from different
MIUs are stored in the corresponding Load Data Records in the Flash
memory of the DCU. The DCU supports communication with any upward
equipment in conformity with RS-232 standard, e.g. a handheld
computer. In most cases, the DCU communicates with the remote Host
Central Station through standard modem via the existing telephone
line or the GSM network.
The Host Central Station (HCS)
is the control center of the system, where all the functions of the
system are controlled and monitored. The HCS passes instructions and
information requests onto the Data Concentrator Units (DCU) by
calling their addresses (or the telephone numbers in case of a
public switched network), and the DCU will respond accordingly. The
address codes (telephone number) of the DCUs are stored in the HCS.
With sufficient mass storage, theoretically all DCUs can be covered
by the HCS, in actual fact the maximum number of DCUs can be
connected to a HCS is about 1000 as it will be limited by the
required response time and efficiency of data management. In case of
failures in self-diagnostics or any abnormal behavior of the MIUs,
the DCU can also make requests to report by dialing to the HCS. The
HCS will convert the data received into a text file compatible with
the corporation's existing Meter Reading Management System, and
store it in the Hard Disk Drive. File transfer between the HCS and
the Corporation's MIS system can be done through standard
input/output ports, such as RS-232. |
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