THE last ten years has seen a dramatic change not only in radio technology but how it is used by instrument and control engineers.
The business case behind deploying wireless instrumenta tion is a compelling one. By elim inating cabling and trenching, users can dramatically reduce the cost of deployment by as much as 70%. Since wireless instrumentation is battery-pow ered, they are much easier to deploy in the field relative to their conventional counterparts.
Wired systems can take days or weeks to be properly installed, whereas wireless instruments require only the sensor to be installed in the process.
So if the business case is that strong and the ROI is solid, why are some still reluctant to deploy wireless instrumentation in their facilities? There are three main reasons:
Reliability:radio signals are subject to reflection as a result of structures, trees, water bodies and buildings.
However, RF design is getting better in addressing many of these issues and by designing highly sensitive radio receivers, and using the transmit power more efficiently with high gain antennas, engineers can estab lish highly reliable RF point-to- multipoint links.
Adaptability: Wireless instru mentation networks are required to adapt to the existing environ ment. It is not practical to move a compressor or a separator just to create a reliable wireless link.
It is sometimes difficult to find a location for an access point or base radio that provides reliable communication with the wireless instruments. Relocating the access point or base radio to improve the RF link with one sensor could result in degrading the links with other sensors in the same network.
Adaptability can be addressed by using lower frequency bands, such as the license-free 900MHz, which tends to provide better coverage, longer range and bet ter propagation, allowing the sig nal to penetrate obstacles. Also, high gain external antennas that can be mounted as high as possi ble on a structure allow access to hard-to-reach sensors which could be located at the bottom of a tank. Improved receive sensi tivity of radio modules also plays a crucial role in ensuring net work adaptability to various industrial environments.
Integration:Managing and debugging dispersed wireless networks presents a new level of complexity to field operators that could deter them from adopting wireless instrumenta tion despite the exceptional sav ings. The wireless network inte gration dilemma is more appar ent in SCADA systems. Since wireless instrumentation net works are supposed to tie into the same SCADA infrastructure available at site to relay valuable operating data to the SCADA host, having the ability to man age the complete infrastructure as one network becomes essen tial. Despite the abundance of tools to capture, process and ana lyze data in the process control market, ensuring data integra tion is still a major problem. Standardising SCADA and wire less hardware from a single ven dor makes it simple to connect remote sites to a central SCADA systems.
Addressing the challenges
A new breed of advanced wire less instrumentation base station radios or gateways is now emerg ing in the marketplace.
This new generation of gate ways integrates both a wireless instrumentation base radio and a long range industrial radio in the same device.
The integrated long range remote radio is configured as a remote device relaying informa tion to a master radio at the main SCADA centre.
The available two serial ports on the radio are configured to tunnel Modbus polling and diag nostic data simultaneously to the wireless instrumentation base radio. This allows operators to manage and diagnose the wire less instrumentation network through the existing long range SCADA infrastructure. Live data and status information for all field units are displayed in a sep arate view or integrated in the SCADA host. On the data inte gration front, modern SCADA host software offers a fully inte grated environment that includes an integrated and scala ble historian to handle more additional data without going through expensive and some times lengthy upgrades.
As the adoption of wireless instrumentation networks increase, users will be faced with a number of challenges to ensure the reliability, adaptability and tight integration with their exist ing infrastructure.
New RF and antenna designs help to address reliability and adaptability challenges.
Hybrid gateways, where sensor network base radio and long range radio are integrated, allow users to view, manage and diag nose their dispersed wireless sys tems from a single point.
Similarly, advanced SCADA host software, with an integrated historian and rapid development environment using templates, can facilitate the integration of new data points generated by a growing network of wireless sensors.
Hany Fouda is VP of Marketing at Control Microsystems, www.controlmicrosystems.com