Australia’s extensive mining operations, water projects, water and waste water treatment plants and pipelines all lend themselves to using wireless to connect remote monitoring systems with centralised SCADA systems and control rooms. But not everyone is convinced.
The last ten years have seen a dramatic change not only in the radio technology but more importantly in how we use it as instrument and control engineers. As more consumers line up to acquire the latest Smart Phones with embedded Wi-Fi, Bluetooth and broad band capabilities, the price of radio modules have plummeted. This has made it easy on industrial vendors to integrate radio modules into a long list of devices and sensors.
The business case behind deploying wireless instrumentation is compelling. By eliminating cabling and trenching, you can reduce the cost of deployment by as much as 70 per cent. Since wireless instrumentation is battery powered, they are much easier to deploy in the field. Wired systems can take days or weeks to be properly installed, whereas wireless instruments require only the sensor to be installed in the process, saving hours or days and valuable resources. Other instruments can be added as needed. If the business case is strong and the return on investment is solid, why are some still reluctant to deploy wireless instrumenta tion in their facilities?
There are three main reasons: Reliability, Adaptability, Integration.
Reliability: In industrial applications, reliability is a major concern. Wireless instrumentation must be as reliable as conventional wired units. Even in simple applications like remote monitoring, users come to expect a certain level of reliability and network availability.
For example, the controls and communications for a wastewater pump station, often located far from the central control room, have to be reliable. If something goes wrong, maintenance people have to be dispatched immedi ately. South East Water Company in Melbourne had that problem. Their dual submersible pump control (Figure 1) required the local controller to cycle between two pumps, ensuring that both pumps were used approximately equally.
The local controller also had to report critical system data, such as flow totals and pump running times to the central SCADA system. Grundy’s Electrics, a systems integrator in Melbourne, installed Control Microsystems SCADAPack controllers, local display panels, and DNP3 opti mised radios at each pump station.
Radio signals are subject to reflection as a result of structure, trees, water bodies and buildings. Furthermore, interference from near-by wireless systems such as cell towers adds more challenges. RF design is getting better in addressing many of these issues. By designing highly sensitive radio receivers, and using the transmit power more effi ciently with high gain antennas, engi neers can establish highly reliable RF point-to-multipoint links.
Adaptability: Wireless instrumentation networks are required to adapt to the existing environment. It is not practical to move a well head, a compressor, tank 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 commu nication with the wireless instru ments. 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 900 MHz, which tend to provide better coverage, longer range and better propagation characteristics allowing the signal to penetrate obsta cles. Also, high gain external antennas that can be mounted as high as possible on a structure allow access to hard-to- reach sensors which could be located at the bottom of a tank. Improved receive sensitivity of radio modules also plays a crucial role in ensuring network adapt ability to various industrial environ ments. For example, the Beypazari water system in Turkey is spread out over 700 sq km of mountainous terrain. They had problems with the distant locations of their alarm systems, so maintenance staff had to visit each pumping station three times a day to check on system opera tion. Because of the high cliffs, a wireless system appeared to be impractical.
Beypazari installed Control Microsystems SCADAPack controllers at each of the nine remote sites. Wireless radios at each site and two wireless data concentrators — one on a hill over looking the town — transmit critical data to the central SCADA/HIM system. The communication network is a mixture of 2.4 GHz radio modems and conventional UHF radio and line modems that are ideally suited to the mountainous locale in which they operate. Also, GSM (a digital mobile telephone standard) was implemented at the central location to provide Short Message Service (SMS) that sends alarms to operator cell phones.
Integration: Managing and debugging dispersed wireless networks presents a new level of complexity to field opera tors that could deter them from adopting wireless instrumentation despite the exceptional savings. The wireless network integration dilemma is more apparent in SCADA systems. Since wireless instrumentation networks 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 manage the complete infrastructure as one network becomes essential.
Ensuring data integration is still a major problem. Some SCADA systems even have a separate historian module that must be purchased as an add-on to handle the flood of data as a result of adding wireless instrumentation networks. A coal seam gas (CSG) opera tion in Queensland had that problem. CSG, abundant in Queensland, is the same as natural gas and is collected from more than 700 well sites scattered across the state. Parasyn Controls, based in Tingalpa, Queensland, is installing Control Microsystems’ SCADAPack controllers at each site (Figure 2) to collect data, provide local and remote control, report events, and communicate with central SCADA systems via radio links. Standardising SCADA and wire less hardware from a single vendor made it simple to connect the remote sites to the central SCADA systems.
A new breed of advanced wireless instrumentation base station radios or gateways is now emerging in the market place. This new generation of gateways integrates both a wireless instrumenta tion base radio and a long range indus trial radio in the same device.
The integrated long range remote radio is configured as a remote device relaying information to a Master radio at the main SCADA centre. The available two serial ports on the radio are config ured to tunnel Modbus polling and diagnostic data simultaneously to the wireless instrumentation base radio. This allows operators to manage and diagnose the wireless instrumentation network through the existing long range SCADA infrastructure. Live data and status infor mation for all field units are displayed in a separate view or integrated in the SCADA host.
On the data integration front, modern SCADA host software offers a fully integrated environment that includes an integrated and scalable histo rian to handle more additional data without going through expensive and sometimes lengthy upgrades. Developing the SCADA screens based on templates allow engineers to add data points easily and rapidly in their systems.
[Hany Fouda is the VP of Marketing at Control Microsystems.]