Many reasons for wireless conversion reluctance are resolved with new technology.
During the last 10 years, dramatic change has occurred in radio technology and, more important, in how control engineers use it. As more consumers line up to acquire the latest smart phones with embedded Wi-Fi, Bluetooth and broadband capabilities, the price of radio modules have plummeted. This has made integrating radio modules into pumps for monitoring, diagnostics, data acquisition and even control easier for industrial vendors.
Pumps are an ideal device for wireless connections. They are often located in remote pumping stations or installed in areas of the plant that are difficult to access by maintenance personnel (Figure 1). But many plants remain reluctant to install wireless control because of perceived problems with reliability and connection to the SCADA system. Modern wireless devices solve these problems.
Figure 1. Bridgeport, Calif., replaced phone lines with a 900 MHz wireless system, reducing the need for operators to visit remote pump sites.
Why Wireless?
The business case behind deploying wireless pumps is a compelling one. By eliminating cabling and trenching, the cost of deployment can be dramatically reduced—sometimes by as much as 70 percent. Since wireless instrumentation is battery powered, it is much easier to deploy in the field relative to its conventional counterparts. Wired systems can take days or weeks to be properly installed. Wireless instruments require only the installation of the sensor in the process, saving hours or days and valuable resources. Other instruments can be added as needed.
If the business case is that strong and the return on investment is solid, why are some still reluctant to deploy wireless pumps in their facilities? There are three main reasons.
Reliability
In industrial applications, reliability is a major concern. Wireless pumps must be as reliable as conventional, wired units. Even in simple applications, such as remote monitoring, users come to expect a certain level of reliability and network availability. Radio signals are subject to reflection as a result of structure, trees, bodies of water and buildings. Furthermore, interference from near-by wireless systems such as cell towers adds more challenges. Radio frequency (RF) design is becoming more effective in addressing many of these issues. By designing highly sensitive radio receivers, using the transmit power more efficiently and high gain antennas, engineers 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, compressor, tank or separator just to create a reliable wireless link to a pump. Finding a location for an access point or base radio that provides reliable communication with the wireless instruments can be difficult. 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.
Integration
Managing and debugging dispersed wireless networks presents a new level of complexity to field operators 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 designed 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.
Despite the abundance of tools that are available to capture, process and analyze data in the process control market, 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 that results from adding wireless instrumentation networks.
Addressing Wireless Challenges
A new breed of advanced wireless instrumentation base station radios or gateways is now emerging in the marketplace. This new generation of gateways integrates both a wireless instrumentation base radio and a long range industrial radio in the same device.
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 obstacles.
The City of Bridgeport, Calif., was using dedicated telephone lines to connect its well pump stations to the central control system, but the system was unreliable. It failed periodically without warning, resulting in inconsistent pump control. Other problems included inaccurate tank-level readings and nonexistent system alarms, which required frequent operator visits.
Bridgeport installed 900 MHz spread-spectrum radios (Figure 2) and SCADAPak controllers at each well and tank site. Pump control is now handled at each site, and the SCADAPak controllers send level, flow and other data to the main control room via wireless.
A similar situation existed at a wastewater treatment plant in Ottawa, Ontario, Canada. The City of Ottawa serves a huge area of 2,758 km2, and the pump sites communicated mostly via dial-up phone lines. The system was not only unreliable, it was expensive.
Ottawa installed 900MHz wireless modems at each pump station and local SCADAPak controllers, which communicate to the main control system via a wireless LAN (WLAN). The WLAN allows operators and staff to access any pump site over a wireless connection from portable laptops. The city plans to install these wireless systems at 100 pump stations, and the cost will be offset by eliminating expensive phone line charges.
Some older wireless installations have not worked out well, but can be updated easily. In 2000, a GPRS cellular system was installed in Sofia, Bulgaria, to help control its water and wastewater system. Unfortunately, the unintelligent GPRS modems were difficult to use and consumed high rates of electrical power at solar-powered remote pump locations. The solution was simple. Modern SCADAPak controller installations at each site solved the communications problem. The SCADAPak manages the reporting of events to the SCADA system, saving bandwidth and reducing network traffic. The SCADAPak saves power with its “sleep mode” and reduced power mode capabilities.
Modern Solutions
Other solutions to wireless problems include high-gain, external antennas that can be mounted as high as possible on a structure, which increases coverage. Improved receive sensitivity of radio modules also plays a crucial role in ensuring network adaptability in industrial environments.
A typical, modern, long-range remote radio is configured as a remote device for relaying information to a master radio at the main SCADA center. The serial ports on the radio are configured 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 information 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 historian to handle 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 to their systems.
Conclusion
As the adoption of wireless instrumentation networks increases, users will be faced with a number of challenges to ensure the reliability, adaptability and tight integration within their existing infrastructure. New RF and antenna designs help address reliability and adaptability challenges. This leaves wireless and data integration with the existing SCADA infrastructure as one of the critical challenges to be resolved. Luckily, hybrid gateways, where sensor-network-base radio and long-range radio are integrated, allow users to view, manage and diagnose their dispersed wireless systems 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.
Pumnps & Systems, October 2010