DATA COMMUNICATION

 

 

 

 

FUNCTION

 

A Telemetry System refers to the subset of a SCADA system that

relies on long distance communications to remote sites. For example,

a major water treatment plant may have a SCADA system in place

for onsite controls with a telemetry system connection that collects

data from the distribution system (e.g. storage tank levels). Collecting

data from these remote sites can be very challenging, especially in

rural or mountainous areas with limited existing communications infrastructure.

 

There are two broad classifications for communications architectures: cabled and wireless.

 

 

Cabled

 

Historically, the easiest way to establish a communications link to a device in the distribution system was to run a cable to it. Since almost all assets used by utilities are on a pipeline, it makes sense to run a communication cable at the same time as laying the pipe.

 

Cables can be owned by the utility and include copper and fibre-optic cables. There are significant distance limitations with copper cables: sending direct analog or voltage/ current signals over a multi-core copper cable is only practical over a few kilometres. Typically, a modem is used instead, converting electrical inputs at the site to digital data and creating an analog audio link to a modem that is located in the control room of the utilities’ operations centre. The modem technology is identical to consumer modems, and therefore the local telecom company telephone lines can be used instead of the utility laying its own cable. In fact, the vast majority of water utilities still use dial-up analog modems, even though they have long been superseded by digital ADSL devices in the consumer space.

 

 

Cabled solutions:

 

  • Standard dial-up: Typically a utility either uses standard dial-up telephone technology to poll the analog modem at regularly periods to gather data and send commands. 300 baud or 1200 baud modems make this slow and restrict data. It can also be expensive when each call carries a fixed minimum “call” charge – low bandwidth, high latency

 

  • Leased Direct Circuit (LDC): LDC is an option where the utility rents a telephone line to the site that is always connected, avoiding the need to dial up the modem.

 

  • ADSL and similar solutions: These solutions useful when much fast data rates and bandwidth required and low latency is required.

    • Security risks as data is effectively sent over the Internet

    • Expensive as each site needs a monthly Internet account

 

  • Fibre-optic cables - tend to be utility owned.

    • Extremely fast, high bandwidth and low latency

    • Fragile, easily damaged and require specialist knowledge

    • Need repeaters ever 20 miles so not suitable for very long distances

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Wireless

 

Analog and digital radio systems are the preferred communications architecture for many water utilities. These systems are owned and maintained by the utility and as such are seen as more robust and secure than third-party solutions, especially at times of natural disasters such as storms and earthquakes when telephone systems may crash.

 

 

Wireless Pros:

 

  • Easy to add to new sites, even temporary sites as long as a mobile signal is available

  • Secure, as data is sent directly without use of the Internet

  • Support encryption

  • Provide data paths over long distances, but usually require line of sight;

  • Support slow data rates of 300 up to about 48,000 baud (2 million times slower than Ethernet)

  • High latency, can be a real issue with mission critical alarms

  • Can be easily installed anywhere in line of sight of a repeater station

  • Do not require the local telephone company, so can be installed in rural locations

  • Can scale up, so may use only the equivalent of an SMS message for regular data updates and switch to a GPRS link when larger amounts of high- speed data access is required (e.g when interrogating an RTU after an alarm is raised)

 

Wireless Cons:

 

  • Data transmission is not guaranteed, utility is dependent on the mobile provider, which can be a significant issue if the mobile network is congested

  • Can be very expensive, as mobile phone providers have not focused on the needs of the utility market, where very small data amounts are required regularly

  • Require permits and licensing for each path and channel, can be costly

  • Using multiple radios on the same channel can be an issue with polling required to communicate to only one at a time, and collision avoidance is required if radios can broadcast at any time

 

While radio systems are still popular other wireless options are now available, where third parties, mainly telecos, provide the infrastructure. Using mobile phone technology (i.e. GPRS and 4G) over GSM networks allows any remote site within range of a teleco’s cell tower to be connected easily to a water utility telemetry system.

 

New technologies for utilities are being brought to the market rapidly, mainly as a result of the explosion in smart metering projects. City wide wireless systems using low powered devices where the utility pays a rental for the architecture are now available and suit telemetry where typically only small amounts of data are collected from each site and polling is many minutes apart. The Internet of Things concept is also making significant advances where devices communicate over a wide range of wireless medium including low power Bluetooth, Zigbee or Whtespace and where low power consumption makes battery powered solution feasible for utilities at sites where mains power is not available.

 

BENEFITS

 

Data communications provides the backbone of any well designed instrumentation and telemetry system. Having access to data that is accurate, timely, and accessible is important to all smart water applications.

 

SYSTEM REQUIREMENTS

 

Each water utility has their own preferred infrastructure, which can include a complex mix of wired and wireless solutions. The key system requirements are that any architecture used is supported and maintained and that it employs standards that allow easy access to the data transmitted over the communications channels.

 

Using currently available third-party solutions like mobile phone technology, ADSL Internet, and modern wireless solutions allows the utility to benefit from their rapid development while simultaneously enjoying the much lower costs associated with mass-produced solutions. Older generation technologies, such analog radio and dial-up modems, may face issues outside of the utilities’ control. For example, telephone companies are pushing to abandon analog modems on their networks as these are not well-suited to their modern digital networks.