- Sensors and related devices, such as pressure transducers, magnetic pickup sensors, digital encoders, temperature sensors, nuclear densitometers, magnetic flowmeters and Coriolis flowmeters.
- Software, such as coiled-tubing fatigue and well bore simulation programs.
- Operating systems, such as Windows XP Embedded, Windows CE and Linux.
- Industry-specific protocols, such as SAE J1939, J1587, J1708; Modbus; Ethernet, 802.11; and Profibus.
"We also like that we can develop software in LabView faster than with most other programming environments," adds Stewart. "It makes the software development side much quicker than our past experiences in C-based programming. What most C programmers take two years to do, we can accomplish in two months."
Foster Flexibility, Secure Scalability
Besides improving programming and enabling control functions, the shift to PC-based control and more capable software also allows more flexibility in designing and configuring many applications. For example, Constance Water Works in Constance, Germany, recently worked with Cegelec Deutschland to replace its obsolete, 20-year-old controls with a PC-based system to maintain secure delivery of 50,000 cubic meters of micro-filtered and ozonated drinking water per day to its 87,000 customers. The new controls consist of two industrial PCs from Beckhoff Automation, which operate as a master and a cold standby, and are linked in parallel with Constance's existing water treatment process, which has three distinct supply channels that were converted in succession to prevent any service interruptions.
"We wanted to use an open-system architecture with modular bus terminals because it was the most economical solution," says Wolfgang Treib, Constance's technology team leader. "The cost of an I/O card 20 years ago buys us several IPCs, including bus terminals today."
Constance's business unit manager Wolfgang Fettke, adds that, "The primary goal for the type and structure of the new control system was to improve plant availability. The decision to use IPCs gave us more freedom in designing the applications, and the current structure also made interfacing to subsystems simpler. The decision to use Beckhoff's system led to significant benefits because sensitive, demand-based control comes with detailed information from many points in the plant. These data are provided by a wide range of sensors. In addition, measuring systems that provide an IP-capable protocol, such as Modbus TCP, can be integrated easily."
Besides the IPCs, Constance also installed six touchscreen, panel PCs for local control of the water. Signal communication with the master control system takes place via the IEC 60870-5-104 telecontrol protocol, and information from about 1,600 data points is transmitted.
Treib adds that Constance's PC-based controls mean on-call staff no longer have to be on-site, especially during weekends, but can conveniently log into the control system via a PC and check plant status. "If a micro-filter fails, the system issues a signal, and the duty officer can check remotely whether one of the two other micro-filters has taken over," explains Treib. "If this is the case, attendance at the water works is not required. We didn't plan for it, but our new control has reduced our on-call deployments, too."
Ironically, once PCs are implemented in some process control applications, they can even look inward to simplify their own operations.
For instance, South Africa-based Richards Bay Coal Terminal (RBCT) loads more than 700 ships per year with coal, using 10 stacker-reclaimers, five tipplers and four ship-loaders, which employ SCADA/HMI systems that used to run on 58 stand-alone PCs. However, these machines are all in constant motion, vibrating and beset by coal dust, which impacted the reliability of the PCs and their servers (Figure 3).
"Reliability problems with standard PCs, as well as the difficulties presented by backups and upgrades, prompted us to look for a more centralized solution based on thin-client technology," says Eric Gumede, RBCT's control systems specialist. Because they're low-cost computing devices that work in an application server environment, thin clients don't require powerful processors and large amounts of RAM or ROM.
The plant was already using Wonderware InTouch software from Invensys Operations Management for its SCADA/HMI systems, so it and system integrator Quad Automation replaced the PCs with InTouch View terminal client servers. They're supported by Microsoft Terminal Services, which is a component in Microsoft Windows that allows users to access applications and data on a remote computer over a network. It also lets administrators install, configure, manage and maintain applications centrally on a few servers.
All application logic runs on the server, while the processing and storage requirements for client machines are minimal. RBCT also adopted Wonderware InTouch HMI, Historian, Historian Clients and Information Server software.
Gumede reports the RBCT's thin-client system reduced engineering costs to its PC budget; improved software integrity; cut power consumption; lessened the risk of theft; reduced downtime on its SCADA systems; increase end-user productivity; and enabled redundancy by making multiple connections possible to different servers.
"Because of the impact non-performance could have on an operation of this magnitude, it was important that both the old and new systems run in parallel before the old system could be removed," adds Gumede. "In my view, the most compelling aspect of this new thin-client system is its scalability and versatility. It's vital for the system to be able to grow to meet business needs and to easily integrate with other systems."