Electronic Design

PACs Address Increasing Green Monitoring Requirements

With the world’s escalating focus on climate change, ever-evolving environmental regulations, and the birth of new markets such as carbon trading, there has been a significant and rapid increase in the demands for environmental monitoring tools and the applications for which they are used. Programmable automation controllers (PACs) can solve these unique challenges.

To comply with federal clean-air regulations, mercury emissions from coal-fired power plants must be continuously monitored. System integrator Data Science Automation (DSA) and its customer, Clean Air Engineering, faced a difficult challenge when recently implementing a mercury emissions monitoring system for a coal-fired power plant.

When evaluating their different options, DSA engineers found distributed control systems (DCSs) to be too expensive and not rugged enough. They also found programmable logic controller (PLC) systems too limited in their Ethernet communication and data handling capabilities.

One of DSA’s main challenges was the remote location of the monitoring system, which would not allow for a local operator terminal. All control and programming had to be performed wirelessly through a PDA. DSA decided to use a PAC because it had native Ethernet capabilities. It also could perform embedded measurements, analysis, and control. And, its software could be used to program the PAC and the PDA.

“To my knowledge, you cannot program a PDA with ladder logic, structured text, or any other IEC 61131 language. We chose LabVIEW graphical programming language to program the PAC and the PDA,” says Richard Brueggman, DSA’s CEO and president. The PAC, which is mounted at the stack, is connected to an Ethernet switch, which allows network communication with the PDA through a wireless access point and wired communication with the plant TCP network.

Another challenge with monitoring mercury emissions is that sampling rates have to be continually adjusted to keep in proportion with the stack flow. DSA performed a variety of tasks with the PAC that addressed this challenge, including implementing control loops that run simultaneously with the data collection, communications, and analysis.

To maintain the sampling flow at a constant ratio to changing stack flow rates, each flow path is controlled by its own proportional-integral-derivative (PID) controller. Each of these loops references user-defined set points in conjunction with measured values to maintain flow and temperature at required values.

With challenging requirements for mixed-signal measurements and complex control, the engineers at DSA noted that the project’s success was due to the processing and automation power of the PAC and the ease-of-use derived from integrating the PDA control system.

Tom Harmon, an environmental engineer and professor of engineering at the University of California, Merced, recently completed an environmental monitoring application in which he documented the microbial biodiversity on a uniquely variable chain of five inland lakes in rural Argentina.

He and his team used a PAC as the basis of their monitoring system, allowing them to address one of the most significant challenges they faced—the large amount of configuration and sensor expertise required to set up a monitoring system.

Traditional data loggers collect data from environmental sensors, but can’t be programmed for any kind of real-time analysis. Typically, the data is collected and then analyzed back at the lab. Some sensors, such as the ones that measure water turbidity, though, are difficult to set up and must be perfectly configured to collect accurate samples.

PACs, however, are completely customizable and can be easily programmed to perform any type of analysis, data logging, and added functionality. In this case, Harmon and his team used NI LabVIEW to create a customized program that runs on the PAC, performing analysis on the data as it is collected and providing real-time feedback on whether or not the sensors are configured correctly.

The added intelligence permits the use of the measurement system without experienced specialists traveling with it. This breakthrough in embedded intelligence will allow the water quality measurement systems to be sent all over the world.

Users also will be able to configure these systems by following simple instructions. The monitoring system then will be able to be used in situations where it’s important to quickly monitor and model water quality, such as when tsunamis, hurricanes, or other natural disasters occur.

Today’s applications involve much more complex tasks than simply monitoring and logging data from sensors. Therefore, they require more sophisticated tools. PACs, which combine the reliability and ruggedness of PLCs with the processing power and capabilities of PCs, offer an ideal platform that addresses these needs.

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