New Device ‘Bridges’ Communications Problems

The water & wastewater industry faces many data communications problems because of the variety of different devices used and the need to obtain information from remote sites. Perhaps the greatest challenge is to link older, possibly obsolete devices to a central control system.

Jul 1st, 1998

The water & wastewater industry faces many data communications problems because of the variety of different devices used and the need to obtain information from remote sites. Perhaps the greatest challenge is to link older, possibly obsolete devices to a central control system.

The Sierra Monitor Communications Bridge is designed to solve all of these problems. The Model 8000 Communications Bridge provides a one-device solution that integrates incompatible PLC, DCS, RTU and SCADA systems. It is designed to meet a variety of communication needs and can increase system performance, improve response time or connect different types of equipment together into a communications system.

In water/wastewater applications the Communications Bridge has been used as a wide-area communications controller to bring together leased lines, dial-out modems, radios and fiber optic lines to a central distributed control system. The system enables the user to be connected to remote well sites, internal and external stations, and the central control room.

As a protocol translator the Model 8000 bridges high-speed, networking applications over RS232, RS422, RS485 or Ethernet communications links. The Bridge can link devices over the Ethernet or link a range of devices using MODBUS, MODBUS+ and Allen Bradley Data Highway together to communicate to a DCS system. The user can connect multiple types of PLCs or RTUs, even obsolete or orphan products.

As a port expander the Bridge allows multiple master devices to access multiple slave devices simultaneously. Multi-protocol support or port sharing allows a single serial port to communicate with many different types of RTUs. Throughput on the system is increased through the use of a proprietary poll-block caching. Caching allows the Model 8000 to accept input from devices at a variety of baud-rates and retains the information until the master device requires the data.

The Bridge can be used to collect data from hundreds of devices, via multiple serial ports. Using a modem, it can be used as a communications front-end to dial many remote sites, connecting a SCADA system to the remote RTUs transparently. Data is buffered internally which reduces the number of polls to slaves, improving overall response. Dual redundancy is offered as an option for mission critical applications.

As a wide-area communications controller, the Bridge connects diverse types of equipment to PLCs or RTUs over dial-up phone lines, leased lines, or radio networks. Systems are easier to debug because it provides complete control over all parameters critical to wide area communications channels, modem dialing and answering commands. Detailed diagnostic displays and statistical reports provide immediate indications of exactly where the problems are arising, down to channel and device level, and also indicate what condition is causing unreliable communications.

The Model 8000 as a wide area communications controller provides:

  • transparent modem control and polling for many different types of RTUs
  • statistical trend and exception communications reports
  • the ability to predial remote sites preparing connection for any protocol
  • configuration options for radio and modem communications including squelch suppression, push-to-talk timers with millisecond resolution and duty cycles

The Bridge’s Hot Standby feature can be used to provide the necessary redundancy on networks. With the hot standby option, if one unit fails the other will automatically take over communication functions.

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