Using modems in remote meter reading
Modems are electronic devices that enable exchange of data over a telephone network between two computers where each is fitted with a compatible modem. In the same way communication can take place between a computer and an electronic meter. Telephone based meter reading is particularly suitable for difficult to read meters and where regular metering is necessary. The use of modems in remote meter reading is growing rapidly in certain countries – in Europe notably in Scandinavia and the UK.
While similar in principle to the modems found, for example, in personal computers, the operational and commercial demands of a meter modem are different. They need to be small, suitably packaged, low cost and dependable.
Modems can provide a means of reading many meters economically and with no infrastructure costs. The telephone network provides an instantly accessible common link to scattered sites and, given a suitable meter, the only equipment required is a modem.
In some cases a dedicated telephone line to the modem will be required. However, an important innovation comes in the form of line sharing modems. These act as intelligent ‘ extensions ’ on a telephone and are able to identify the origin of incoming calls using CLI (caller line identification) a service provided on modern telephone networks.
The modem decodes the origin of an incoming call from signals passed over the network. When the subscriber number of the data collection computer is identified, the modem answers the call before the parallel telephone rings , thus providing ‘no ring’ calling. It also prevents unauthorised remote access to the meter.
A meter modem must be reliable, with a life of 10 to 20 years, and be able to tolerate extreme temperatures. An ideal modem for remote meter reading should incorporate a ‘watchdog’mechanism that resets the modem in the case of a brown-out failure to facilitate permanent unattended operation . Ability to withstand lightning strikes on the telephone line is also advantageous.
Usually the amount of data to be collected from a meter is small. A modem operating at 1200 or 2400 bits per second is usually the most suitable, having a quicker call set-up time than ‘faster’ modems. This means that the overall time of the data collection call is shorter and the communication quality better where local line quality may be poor. Such ‘slow ’ modems are also lower in cost.
Interfacing and DC power provision to the modem must be checked against a meter for compatibility. Modifications to standard modems may be needed, or adaptations fitted on the meter. The operation of the modem may also depend on the method of operation of the data collection computer. Modems must also comply with local safety standards and be approved for connection to the telephone network. Buying a meter complete with a modem is a way of obtaining some confidence in these matters .
Most modern meters have provision for connecting a modem directly, particularly in the case of electricity meters which are produced with a communications
port. Water, gas and heat meters often provide only a simple form of electronic interface, typically in the form of a pulsed output, meaning that there is no power for the modem.
Data storage for such meters requires an electronic data logger, which needs to be integrated with a modem to achieve remote reading. Such a combination of equipment can be difficult to cost justify. There is minimal data to be logged in many water and gas metering applications, and a solution that combines both functions in one package will provide a much lower cost. To this end Coherent is developing an ‘intelligent modem’ that links to the meter pulse output, logs and stores data and is powered by battery.
Reliable modems already provide economically viable meter reading by telephone in many countries. Line sharing and intelligent functionality in a modem open the way to economic reading of many more meters, not only in industry but also in some domestic sites.