Tele-metering systems

Definition

Telecommunication channels transmit to the central point a process in which measurements are periodically made from remote locations.

In the case of home appliance field, tele-metering systems are strongly connected to the accounting systems implemented for the majority of the utilities existing in house.

The measurement can be realized using the network interfaces existing on the metering instruments, such as: energy counters, water and gas counters or other counters like the heating counters.

Animation 1 The System Block Diagram of automatic meter reading (AMR)

The automatic meter reading (AMR) can be realized in two different ways:

• Using an existing network such as: PSTN network, GSM/GPRS network, or PLC (power line carrier) system. In this case, the central system will address to each instrument that would reply the metered values after the updating of measured data.

Animation 12 The traditional Tele-metering System

Animation 2 GSM/GPRS Tele-metering System

• Usage of mobile data concentrators, like Personal Digital Assistant (PDA) permit (wireless link) to temporally connect to the instruments, to ask about the last measured values and, in the end, to receive the results. 

System functions and effects:

• A periodically reading of measured values from the metering instruments. An easier hourly, daily, monthly data reading. On the other way, the AMR system can verify the upper and the lower data limits, the statistical measured values (average, standard deviation, variance, load curve) from the previous month, previous year, and check the plausibility of measured data.
• An automatic billing, for energy and utilities consummated by each consumer (bill calculation, detailed bill checking billing, tax calculation).
• On-line monitoring of consumptions in house could be another function of system.

We can see some features and advantages of system, such as:

• Presents a user-friendly operating environment.
• Includes a LCD display that is used by the costumer to the local control of the consumptions.
• The maximum sampling rate of AMR, that means an interrogation through the network of 2000 devices per minute.
• A “single case” solution, which combines the tele-metering system with the household electricity distribution system, realizing a compact solution for the majority of houses.
• Frequently, the tele-metering systems will use existing telecommunication systems such as: telephone line modem, wireless telephone modem, RF communications existing in the house, in order to transmit measured values to the central station.

Advantages:

The de-regulation of the electricity market has been carried out with a view to modulating the best possible contracting (demand) of power generation and consumption. For this reason, the power on this market is settled up using an hourly price. For large consumers, it is mandatory to install remote metering equipment with each 15 minutes recording facilities.

So that the retailer can quickly adjust and balance its demand at the pool to the real demand of its consumers, thus avoiding the extra costs of consumer deviations and more efficiency running of distribution energy system (DMS).

More than that, in the new vision of distributed energy management systems (DEMS), some of these actors on the energy market can provide services for the DMS such as the ancillary services, which improve the balance of whole system with minimal prices.
The installation of tele-metering equipment brings with it considerable advantages:

• Contracting of any billing mode, even the most complex.
• Digital display of power ratings and energy. Therefore, the metering is more accurate.
• Storage in memory of billing information from previous periods.
• Instantaneous on line access to billing information. It allows remote reading of consumption data for each consumer, using the dial-up system or other remote connection.
• Recording of power cuts, with indication of the blackout’s  time and of the moment when power is restored.
• Through the installation of a specific programme, it is possible to perform billing simulations, so as to be able to anticipate the amount of the bill.
• In UK, the company provider for electricity has introduced a special kind of billing system using pre-paid system, which allows consuming up to the limit of pre-paid money, paying a special fee upwards.
• It allows the management of the consumption status and invoicing from multiple sites to be monitored from a central location.
• Graphic displays can be obtained to show the quarter-hourly load and power ratings for the optimal renewal of contracts.

Description of the system:

The implementation of AMR system includes field elements such as: counters, RTU (Remote Terminal Unit) or other sensing elements with digital interfaces, like: RS485, RS232, IR interface, Ethernet interface, or RF/Bluetooth interfaces.

The commands and the reading values are transmitted using specific communication protocols, such as: IEC60870-5-102, IEC61850, IEC60870-5-101, IEC62056 and so on. These allow not only to communicate but are able to include verification of transmitted data, validation of requests from the central station and other services like dispositions to the end user to change the profile of consumption.

The field elements could be linked to the central station directly through the network, or they could be connected by intermediate elements, such as: data concentrators, communication modems, radio modems and so on.

At the central station level, the corresponding modems or interfaces are present and assure the conversion of data in a digital format. The central station can adopt two kinds of methods in order to access the field measuring points (RTU/counters):

• Pooling each of RTU, by addressing and after reading the data, at self initiative;
• Accepting interrupts that are generated by each of RTU, which realize periodically the measurements.

 So, after each measurement session the RTU will generate a request message for using the common bus. At to this message the central station will react by accepting (acknowledge) after arbitration of request. A transfer session will begin and the RTU will transfer the data acquired. Generally, messages are coded in order to assure the reliability of data and to prevent some possible insertion of hackers at the level of transmission channel.

How can we integrate the local metering elements in a complex billing system ?

The remote Automatic Meter Reading (AMR) System is a host driven, multi-level network system consisting of:

• Central Station (CS),
• Data Concentrator Units (DCU) and
• Meter Interfacing Units (MIU), with built-in flexibility and expandability.

An usual Automatic Meter Reading (AMR) system block diagram includes: Central station (CS), Public Switched Telephone Network (PSTN), GSM/GPRS network, Data Concentrator Unit, Meter Interface Unit, Multi- Functional Energy Meter, Pulse Meter, Mono Phase Electronic/ Mechanical Electric Meter and Three Phase Electric Pulse Meter, Gas Meter, Water Meter.

Central station (CS)

With additional hardware and software support, either the CS can function as a workstation in an existing Local Area Network (LAN) and becomes a member of the entire system, or several CS can be connected together to form a network of their own.
Automatic Meter Reading (AMR) system can be connected to any Electricity, Gas, Water and flow Meters with pulse output for Meter Readings.

The Central Station is the control centre of the system, where all the functions of the system are controlled and monitored. The CS passes instructions and information requests onto 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 numbers) of the Dues are stored in the CS.
Other functionalities of the host central station are:

• Centralized management and remote setting by DCU.
• Automatic classification and storage of data, providing data interface for user.
• Generation and printing of various reports.
• Prompt online help to make easier to operate the system.

Public Switched Telephone Network (PSTN), GSM/GPRS network

PSTN refers to the international telephone system based on copper wires carrying analogue voice data. This is in contrast to latter-day telephone networks, based on digital technologies, such as ISDN (Integrated Services Digital Network) and FDDI (Fibber Distributed Data Interface).

The public switched telephone network (PSTN) is the concatenation of the world's public circuit-switched telephone networks, in much the same way that Internet is the concatenation of the world's public IP-based packet-switched networks. Originally a network of fixed-line analogue telephone systems, the PSTN is now almost entirely digital, and including mobile as well as fixed telephony

. The most basic tele-service supported by GSM (Global System for Mobile Communications) is telephony. As with all other communications, speech is digitally encoded and transmitted through the GSM network as a digital stream.

GSM users can send and receive data, at rates up to 9600 bps, to users on POTS (Plain Old Telephone Service), ISDN, Packet Switched Public Data Networks, and Circuit Switched Public Data Networks using a variety of access methods and protocols, such as X.25 or X.32. Since GSM is a digital network, a modem is not required between the user and GSM network, although an audio modem is required inside the GSM network to inter-work with POTS. Switching Centre (MSC), performs the switching of calls between the mobile user and between mobile and fixed network users.

GPRS (General Packet Radio Service) System is a new no voice value added service that allows information to be sent and received across a mobile telephone network. GPRS can be much faster than other traffic on GSM but the exact speed a single user sees will be directly related to the total number of users in a cell.

However most GPRS transactions will be short hence reducing any delays. GPRS is designed for the Internet hence Internet services such as File Transfer Protocol (FTP), Web browsing. Because it uses the same protocols, the GPRS network can be viewed as a sub-network of the Internet with GPRS mobile phones being viewed as mobile hosts. This means that each GPRS terminal can potentially have its own IP address and will be addressable as such.

Data Concentrator Unit

Data Concentrator Unit has the following characteristics:

• Usage of Ethernet LAN/ Internet for Remote Meter Reading and Data Management.
• Support all functions (data reading, time-triggered operation and management) of the AMR system.
• Able to transmit data to higher level hosts station through PTSN and GSM network (or any other RS-232 standard communication facilities and channels).
• Standard RS-232 interface, which facilitates site debugging and data checking.
• Communicates with lower level Meter Interface Unit (MIU) and Multi-channel Meter Interface Unit (MMIU) using power line.
• Able to issue broadcast commands simultaneously through all 3 phases of R, S and T.
• Large capacity solid-state disk to store all types of data.
• This will help to reduce the frequency of connections to host station and increase the efficiency of each connection.
• Automatic check at the voltage levels of 3 phases. The time and duration of all blackouts and disruptions of any phases is logged. It is able to perform self-diagnosis and monitor the working conditions of MIU and MMIU. It is able to record and report any abnormalities to the higher-level host station.

Meter Interface Unit (MIU)

MIUs and meters connected to it can be considered as sub-systems of the CS. 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 CS 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.

Both the MIU and the DCU contain the PLM (Power Line Modem) device. The binary data stream is keyed onto a carrier signal by means of the Frequency Shift Keying (FSK) technique. 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.

Multi- Functional Energy Meter

Functions:

• 1-4 fee rates,
• 1-10 time periods per day, 1-10 time zones per year, 1-2 holidays per week, public holiday schedules for 10 years.
• Measuring the active and reactive total and each electrical energy rate, the maxim demand and the occurred time, total and each rate energy of 1-4 quadrants
• Recording the cumulative time, times of each broken phase, the active and reactive cumulative energy in broken phase period, the starting and ending time of the latest, broken and the latest 64 times of power-off.
•  The interval can be settled and it records the load curve in load representative day mode and load curve record mode.
• Programming and reading the meter by PR 300 infrared meter-reading unit and handhold unit, and RS-485 port to remote meter reading and programming, support the electrical energy broadcast frozen instructions by RS-485 field bus.
• Recording the reset times, time and cumulative programming times, the latest programming time and unit code of programming.
•  Pulse output is 3 or 4 optical coupling and each can be set to output individually different contents.

Multi- Channel Meter Interface Unit

Support all functions (data reading, time-triggered operation and management) of the AMR system.

• Compatible with Meter Interface Unit (MIU), it is a combination of Meter Interface Unit (MIU) and Multi-channel Meter Interface Unit (MMIU) that can be installed at the same time in a local area. This is a significantly practical approach. Some meters are inevitably dispersed in a local area. For instance, in a 3-phase metering system there are some meters located remotely apart.
• Each MMIU can manage up to 16 electric meters requiring a dedicated line to the MMIU and having a shared earth connection.
• Supporting the use of infrared transmission for initialization and data reading. Alternative of 3-phase and single-phase power supplies versions.
• Pulse signal is isolated by photo electricity to ensure reliable operations.
• Storage of data into RAM, which does not need power supply to maintain memory.
• Low power consumption of below 0.1W on the average.
• Lead fused connection to be metered.

Pulse Meter

 Single-phase meter series were designed for long-life use. They have the feature for wide-load, a high overload tolerance, long-life and exceptional measurement stability and reliable performance.

Mono Phase Electronic/ Mechanical Electric Meter and Three Phase Electric Pulse Meter

Support all functions (data reading, time-triggered operation and management) of the AMR system.

Characteristics:

• Fit for different models and makes of electronic and mechanical electric meters
•  Especially suitable for the situations where meters are installed dispersedly
• Compatible with MMI
•  Power line carrier communication
•  Provide special indication (e.g. average indication)
•  Every Meter Interface Unit (MIU) has the relay capability
•  Metering initialization contents: meter constant, window value and MIU address (8 decimal digits)
•  High quality AC/DC scheme with high resistance to disturbances
•  Storage of data into RAM, which does not need power supply to maintain memory

Gas Meter

1. Two-way Data Communication by Power Line Carrier
2.  Compatible with Electricity Meters and all MIUs can be used in the same Data Concentrator Unit (DCU)

Gas flow meters are used for measuring the flow or quantity of a moving gas. With most liquid flow measurement instruments, the flow rate is determined inferentially by measuring the liquid's velocity or the change in kinetic energy. Velocity depends on the pressure differential that is forcing the liquid through a pipe or conduit.

The basic relationship for determining the liquid's flow rate in such cases is:

                                                      (1)) 

Where:
Q = liquid flow through the pipe
V = average velocity of the flow
A =cross-sectional area of the pipe.

Water Meter

Water Meter is a meter for measuring the quantity of water passing through a particular outlet. The meters take the potential generated by the electrode and convert it into units of concentration.

Installing a meter can reduce water usage and could save money. Paying for what you use also means that less water is wasted which helps conserve valuable water resources. Characteristics are the same with those of gas meter.

Automatic meter reading system (AMR)

The trends of AMR system is to integrate in a unique form all the utilities existing in house. In the same time a wide form of communication channels coexists in most of implementations. This is the result of a historical evolution. That means that traditional communication and wireless systems are included in the same functional network that implements the communication part of an AMR. Also different type of software such as:

• IP solutions – GPSR, Ethernet -, that include a dialog like client-server solution
• Classical dial-up sessions based on call and corresponding response, specific for PSTN, GSM- leads the message transmitted through the network.

In our example (see animation 14), the central station includes Ethernet connection and also wireless connection.

Animation 3 Structure of a complete AMR system

All the measured values are stored at the level of the central station, in correlation with the time (time stamp), the registered users, the corresponding tariffs and the bills for each of them. An SQL server manages this database.

The data will be accessible by the utility company and also by each user for own interest data. A WEB server connected at the database assures the data visibility for the users, and the access is realized through the Internet connection (client-server model), with authentication.

The acquisition system (AMR) uses the concentrator of the data and RTU in order to collect the information. A reliable and secure protocol is implemented in order to avoid possible insertion of hackers in system. Periodically data are acquired.

The new solution (DEMS –Distributed Energy Management System) will provide some new functions such as: volt-var regulation at the level of users that are micro-generators, demand side functionality, and/or ancillary services that implement different form of balancing of power network, and so on.

Details concerning traditional outbound and gsm sms inbound commercial & industrial electric meter reading system

Traditional outbound Commercial & Industrial electric meter remote reading system

Network codes had to be introduced to govern the interaction between suppliers, transporters and electricity vendors, and the demand from the main commercial and industrial (C&I) customers had to be monitored daily.

Traditional AMR systems which use short range RF transmission to a local data concentrator could not be used economically, because C&I meters do not have the density of residential meters.

Most utilities opted for a telephone-based outbound system, where a telephone modem is connected to the serial port of each C&I meter and the meter is called daily by the data collection computer, although other forms of public network such as wireless, X25 have also been used. Remote metering of C&I meters is comprised of a smart (interval) meter with serial communication and often IEC 62056-21 protocol, plus PSTN/X25 modem and outbound polling server.

The Public Switched Telephone Network provides switching and signalling for local, long distance and international voice and low speed data calls. A modem links into the PSTN and can be used for a permanent connection.

Most phone lines were designed to transmit analogue information - voices, while the computers and their devices work in digital form - pulses. So, in order to use an analogue medium, a converter between the two systems is needed.

This converter is the MODEM, which performs MODulation and DEModulation of transmitted data. It accepts serial binary pulses from a device, modulates some property (amplitude, frequency, or phase) of an analogue signal in order to send the signal in an analogue medium, and performs the opposite process, enabling the analogue information to arrive as digital pulses at the computer or device on the other side of connection.

The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Primarily used to communicate via telephone lines, modems can be used over any means of transmitting analogue signals, from driven diodes to radio. Dial-up modems can establish point-to-point connections on the PSTN by any combination of manual or automatic dialling or answering.

GSM SMS inbound Commercial & Industrial electric meter reading system
Today GSM is truly a global form of wireless communication. GSM had the merit of not needing a phone line.

The primary aim of the GSM networks originally was to service voice calls. Operators and hardware developers have therefore turned to new GSM network services, including machine-to-machine communications (M2M), text messaging (SMS) and GPRS. M2M services today represent a major opportunity for growth for the GSM business world and GSM has become a viable and competitive form of data communication.

This system is inbound, and the GSM/SMS device can be switched off during periods of inactivity, which greatly reduces its power consumption. The SMS method of data communication is well suited to interval and other commercial meter reading, as the small amount of data is contained in one text message.

The reading is sent to the GSM network, an acknowledgment from the network is received, and the device can be switched off until the next day. The SMS is securely held in the SMSC of the operator and is recovered by the data collection computer, provided it is linked in a suitable way to the SMSC through a high speed permanent connection.

Table Comparison of communication technologies (Source: Metering International 3 / 2004)

		GSM			PSTN
		SMS	Data Call	GPRS
COST	Connection	Excellent	Excellent	Excellent	Poor
	Modem	Good	Good	Good	Excellent
	Operation	Excellent	Good	Good	Fair
TEHNICAL	Easy of Installation	Excellent	Excellent	Excellent	Fair
	Low Power Operation	Excellent	Good	Poor	Excellent
	Scalability	Excellent	Fair	Excellent	Fair
	Compatibility with existing data collection	Fair	Excellent	Good	Excellent