This article provides an overview of the relative technical merits and costs of different forms of telephone network connection of meters, with the emphasis on metering of the smaller C&I consumer.
Telephony in RMR offers readily available communications without the cost of infrastructure. Telephone penetrates virtually all C&I premises worldwide, and is well established as a channel for collecting meter data from larger industrial consumers. Except in C&I parks, which may be more suitable for RMR using local wireless or PLC (powerline communications) to local concentrators, C&I meters are typically widely dispersed and telephone is the obvious network to which to connect.
There are broadly three types of telephone network that are publicly accessible and do not require proprietary communications equipment. These are:
• The analogue landline network (PSTN) which is the oldest and most wide spread and provides generally reliable communi cations throughout the world.
• Cellular networks of various standards, of which GSM is the most widespread with over 750 million personal mobile phones connected in over 180 countries.
• ISDN, the digital network connection standard.
ISDN has limited penetration, even in North America and Europe, and that mainly into larger enterprises. Its growth may be affected by the arrival of broadband, which has much higher data transfer rates. There also appears to be a dearth of suitable low cost ISDN interfaces engineered for easy connection to C&I meters. These factors imply that analogue landline or cellular connections offer wider, easier and cheaper solutions than ISDN.
Connecting a meter to a cellular network is generally a quick process, without line installation costs. Cellular telephone networks are used in RMR applications in many countries. While cellular modems have fallen in cost over recent years, they are still more expensive than basic landline modems. Meter operators typically pay around US$/€150 to US$/€375, depending on model and quantity. Connection and subscription costs in many countries have also come down and in most cases are lower than dedicated landlines. Special tariffs are available from cellular network operators in many countries, and in some circumstances are cheaper than landline.
To a large extent call costs depend on what a meter operator can negotiate with a carrier, cellular or landline. Most calls to meters can be made at night, particularly with automated collection systems, offering the potential for negotiating very cheap calls indeed. Cellular call costs seem likely to continue to decline as cellular network operators compete for share of data connections as mobile voice connections reach market saturation level.
Not all meter sites are suitable for cellular telephone connection. Some users have experienced extended call times and dropped calls, with occasional network congestion in local areas. Some GSM modems operate at not less than 9,600bps (bits per second) while the maximum transfer speed from a meter might be only 2,400bps, or the collection computer might be fixed at 1,200bps.
There are currently few cellular modems engineered to fit utility meters, especially older meter designs, so that many meter operators have had to fall back on more generic ‘terminal' type cellular modems which might be unsuitable. For example, it is a good idea to check if the product under consideration can hold its settings in memory if power from the host meter is lost. Cellular modems are particularly power hungry in relation to the DC supplies available from communications ports of many electricity meters, so they require access to an AC supply and provision of a transformer. However, a GSM modem engineered specifically to work with a meter that overcomes such problems has, for example, been produced for use with the PRI Premier meter.
In general, analogue landline telephone is reliable, with good quality data and with few interruptions in communications. It is usually a simple procedure to connect modems to landlines. A dedicated telephone line to a meter will incur periodic subscription charges and possibly charges for new installations that can be costly if the meter is in a difficult location. There can be delays in getting a line installed. A solution to these problems can be special modems which, when fitted to meters, eliminate separate meter line rental and installation costs by sharing an existing telephone line.
For line sharing in smaller C&I premises it is desirable to use equipment to eliminate telephone bell ringing on a data call. Line sharing by modems can be achieved in a number of ways. The two more common methods are by using Calling Line Identity (CLI) decoding on dial-outbound systems (data collection computer calls meter) or by dial-inbound operation (meter calls computer).
There are potential problems with CLI operation. In some countries the telephone company charges to provide the CLI signal on incoming calls; no-ring calling is only achievable in some countries; and the CLI signal cannot pass through PBXs to internal extension lines. In calculating installation costs, however, it should be noted that even with line-sharing landline modems there is the cost of running telephone cable from the meter/modem to a telephone line junction box or extension socket.
There are many suppliers of industrial quality analogue landline modems with varying degrees of technical suitability for C&I metering. Costs range from around US$/€25 to US$/€500 depending on operating specification, environmental tolerance and general quality. They provide line transmission speeds varying between 300bps and 28,800bps.
For C&I interval meters the amount of data to be transferred is small, and a low cost 1,200 (V22) or 2,400bps (V22 bis) modem is perfectly adequate. Connect time is faster with these less complex modems so that call time can be shorter than for ‘fast' modems if data volumes are small. Modems of higher standards than V22bis are often too large to fit inside a meter, which can present a security problem, and many meters do not provide sufficient power for modems operating at more than 2,400bps. Some meters do not support more than 1,200bps/baud across the meter/modem interface, so a ‘faster' modem may be useless in any event.
Dial-inbound is a better line sharing method, as it can be applied almost universally and provides a complete ‘no-ring call' solution. Howard Stark, MD of Stark Energy Information Systems, believes that dial-inbound operation using analogue landline modems makes a significant contribution to reducing communications costs. His company is planning further development of its software to handle large scale dial-inbound meter networks. By such means he expects fast growth of interval metering in electricity supply for smaller C&I consumers, not for settlement purposes but solely for energy management. Coherent Technologies holds the same opinion and has developed an ‘intelligent' low cost modem capable of autonomously generating telephone calls to the collection computer, so that it can be fitted to ‘dumb' meters and existing meters that cannot be upgraded to generate calls themselves.
The use of the Internet in small C&I metering needs some comment. The basic technology to turn meters into simple Internet servers is already available, from companies such as Connect One Semiconductors Inc. Web-enabling of meters may come from meter manufacturers, although a more flexible approach might be to build the functionality into the modem. There are generic modems of this type already available, although seemingly none yet engineered for use in meters. However, at present the idea of using Internet server modems increases the cost of communications on a meter. Further, a telephone line to a remote meter, with its expense, is still required if the meter network is dial-outbound.
A key issue in creating viable RMR for smaller C&I consumers is cost reduction. Web-enabling of meters in a wide area network does not seem to be a move in that direction. An interesting combination of techniques is used in the utility metering data loggers of UK company Technolog Limited to minimise costs and take advantage of the Internet. Their Cello battery-powered logger uses the GSM network to send data periodically to a PC. The SMS (Short Messaging Service) is used to transfer the data. The metered information of many data loggers can then be made available on a secure website. Although it uses a GSM modem, this solution provides a good combination of low cost installation and very low cost GSM SMS tariffs, plus access to management information via low cost connection to a website. Technolog also produces systems that use the landline network.
There are surprisingly few modems for any telephone network that are specifically designed to fit meters and that work well in a metering environment, although the number of specialist RMR modem suppliers is increasing. There is no one perfect telephone solution for all RMR networks. What is used will depend on individual business, local and technical issues. Dial-inbound meters/modems sharing standard telephone lines are likely to be used more frequently, as they offer a low overall cost combined with installation requiring minimal technical skill and reliability of communication.