Sensors Working Overtime
By Timm West
The familiar pressures on manufacturers of faster time to market, minimizing costs, and doing more with less apply equally well to engineers dealing with control issues. Technology trends continue to make an engineers’ job easier. But at the same time, changes in technology can also pose challenges of how best to integrate new technologies into existing processes.
Understanding what the trends are and how they impact existing processes as well as how they might help in future projects is crucial to success. Specifically, there are several key trends impacting the design, operation, and implementation of flow control components in wider control systems. Even though some of these trends are not entirely new, it’s still important to keep them in mind and be aware of their impact. Here’s a look at some of those trends and what they mean for design engineers, plant engineers, and engineering managers.
An ongoing trend in the flow control as well as the broader control industry is toward increasing miniaturization. Global competition is forcing plants to shrink costs by building smaller facilities. As a result, plant equipment needs to have a smaller footprint. Power and communications products have steadily gotten smaller and more compact. Consequently, control components are following a similar path to miniaturization.
Flow control components have been able to shrink in size thanks in large part to advances in silicon technology. Specifically, the physical size of electronic components and processors has enabled control component manufacturers to not only shrink package size but combine functions that formerly were spread out among several separate devices into one package. This reduces component count and saves space.
Reducing size has other benefits, such as components being able to fit into applications where they couldn’t before due to size restrictions. One example of this is a flow switch used aboard an aircraft carrier to sense jet fuel flow. This particular system uses laser contaminant sensors to analyze the purity of the jet fuel aboard an aircraft carrier. A laser sends out a beam that passes through the fuel. The reflections of this beam are then analyzed to determine the amount of contamination in the fuel and thus assess fuel purity. The problem was that the lasers were staying on all the time and would burn out, making for a costly repair. Since the laser sensors could only analyze jet-fuel contamination levels with the fuel flowing, inserting a flow sensor in the pipeline sensed when fuel wasn’t flowing and turned the lasers off, thus prolonging the life of the lasers.
Intelligence at device level
The continual scaling of silicon has meant ever-shrinking and more powerful electronic circuits. Smaller electronic processors are increasingly more powerful and can fit in places where they couldn’t before, such as inside of flow control components. This increase in intelligence at the device level is becoming more and more common. In closed-loop control systems, the demand is for decision making to take place at the point of application, not at a distant PC or PLC. So components are being asked to not just sense conditions but control them as well.
Some flow control monitors now come with added intelligence to control the processes they’re monitoring. For instance, a flow monitor in a pneumatic system can detect leaks in the system and shut off pumps when they aren’t needed. Since electricity rates are based on peak usage, such an intelligent monitor can save energy costs. Such flow-control monitors can also be programmed to have compressors share loads and rotate demand, which also can cut energy costs. These intelligent devices can also store data such as peak usage, current, and time. This data can then be used at a later time to generate reports for analysis.
In a process gas-flow monitoring application, a flow-control device inserted into a pipe can provide an analog signal proportional to mass flow rate. Such devices are programmable and can also store high and low flow rates and temperatures which can be recalled later for further analysis.
The need for speed
Doing things faster generally results in being more productive. Increasing production means having machines that run faster and more efficient. But faster machines also require more responsive controls. Improvements in response times of even a few milliseconds can dramatically increase throughput.
At the component level, this translates into increasing the control component response time. One way to do this is to take advantage of the continuing advances in silicon technology, in the form of faster microprocessor chips. Doing so means that control components can respond to events quicker. Also, many microprocessors now have signal processing capabilities which adds intelligence at the component level and lets control components make decisions that were once solely the function of PLCs and PCs.
As recently as a decade ago, plant workers with clipboards could still collect data by walking up to a meter, reading a value, and recording it on a sheet of paper. Not any more. Distributed control systems have changed all of that. And with processing plants spread out around the globe from the Arctic Circle to Iraq, some of which have no on-site personnel, the need to remotely monitor and control events and processes in these plants is crucial.
No longer is it adequate to just sense conditions and sound an alarm. Nor is it enough to do a manual reset. Systems now require the capability to be remotely resettable or turned on or off. And increasingly, networks of wireless sensors and controllers are in place to do the job.
The increased demand for remote control and monitoring requires reliable communication networks. Flow-control components need to communicate with other control or monitoring systems to indicate and report on status and to take control actions when necessary. This communication can take place over any number of different networks such as Foundation Fieldbus, Ethernet, Profibus, or a number of others including an ever-increasing array of wireless networks.
Communications are essential especially for plants located in remote sites such as refineries and pump stations. Such facilities usually have no personnel on site. In this case, a remote operator can communicate via an Internet connection to turn pumps or valves on and off or to check the status of plant operations.
Another key trend is the increasing use of sensors throughout processing plants. This lets plant operators know more and more about the processes they’re running and controlling. Plus, more data from sensors allows for tighter control over batch quality. It also leads to more efficient use of raw materials and energy, which ultimately increases production speed and JIT maintenance.
However, the ability to compile, analyze, and respond to the data received from this myriad of sensors can be quite a challenge. For increasingly intelligent flow-control components, this means having the ability to do several things such as store data, communicate effectively and reliably with interconnected control systems, and take control actions when necessary.
Taken together, these trends are influencing how flow comp
onents are being designed and implemented in control systems across a broad range of industries. Even though these trends may not be entirely new, being aware of them makes companies more responsive to customer needs as these trends continue to impact the way plants and manufacturers do business.
Timm West is an applications engineer with E-T-A Circuit Breakers.