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“Interest in the basic fundamentals of sensors has decreased in the last 30 years as people have retired,” says Johnson. “This is why some users ask us for transmitters with 0.10% accuracy, and then they go buy a sensor that can be off up to 10 °F at different temperature levels. People know about transmitters, but they don’t know about sensors. In fact, the president of JMS Southeast recently met with the head of the instrumentation department at a university in Charlotte about RTDs at 0 °C, and it was the first time they’d heard of sensors.
“For example, I recently built a cedar house, but unfortunately I used galvanized nails that chipped and bled. I remembered too late that I should have used aluminum or stainless-steel nails. The same rules apply to industrial process control. You can’t forget the fundamental things that are naturally part of process control. However, we’re not teaching enough about commodity technologies and how to apply them correctly, and so price pressure wins because users think the components are all the same. If a thermocouple costs $100 and the rest of the system control panel costs $10,000, then people think why should they care a about the lower cost item? They don’t realize how the thermocouple may affect their whole system. Sometimes you just have to pay attention to the basics, but we often see them being overlooked.”
To help users learn about thermocouple and RTD basics, JMS produced and offers a 3-hour DVD of its training course. Johnson also recommends Industrial Temperature Measurement by Tom Kerlin and Bob Shepard, published by ISA. He also suggests that user consult the appendices to ASTMs standards for thermocouples, RTDs and testing devices.
Though temperature measurement devices remain essentially unchanged in their basic operations, the data processing, emerging software and intelligence around and above them continue to evolve rapidly. For example, all of Meadwest Vaco’s devices usually shoot their signals and loop data back to its DCS, but it and other DCSs also are evolving. In fact, the company recently replaced its DOS-based DCS from Yokogawa Corp. of America with Yokogawa’s CS 300 Microsoft Windows-based DCS.
“It’s all point-and-click, so it’s much easier to program and maintain,” says Brackenridge. “Our networking is still all point-to-point 4-20 mA, but I don’t know if we might try a fieldbus in the future.”
Despite this ease of use, Brackenridge adds there was some initial resistance to Meadwest’s updating its DCS from some of its mostly older operators. So, not only should less-experienced engineers learn from the veterans, but those older engineers also could stand to learn a few new tricks too. “We did a lot of talking, coaxing and training about the new DCS, but sometimes we also had to say that the new way is just the way it is,” says Brackenridge. “We even set up a simulated process, so our operators could see how the application would react when they used the new DCS to manipulate valves in manual and automatic.”
Whether wired or increasingly wireless, the sheer number of temperature and pressure points and other variables being measured are all but certain to increase in the future.
“The role of pressure transmitters is changing to include even more process diagnostics and advanced process control, which we call statistical process monitoring. Basically, pressure transmitters can now do stuff that control room couldn’t do in the past,” explains Nelson. “And having transmitters all over a plant gives users a more physical connection to their processes, as well as very fast processing and update rates. This means users can employ pressure transmitters to help see if a distillation column is flooding, or if an application’s fluid composition has changed due to entrapped air or another kind of instability. For example, fluid catalytic crackers (FCCs) need constant flow-rate data, and new pressure transmitters can more closely monitor the overall health of these processes by monitoring for statistical variations.”
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