Have you seen the TV commercial for an insurance company, where a woman says to a friend, “Well, did you know, that when a tree falls in a forest and no one is around, it does make a sound?” Cut to a personification of a tree then actually falling, complete with a terrified shout as it is uprooted. I have to admit, I laugh every time.
Of course, when a tree falls in a forest, it does make a sound, though I doubt it actually says, “A little help here?” to the surrounding trees. Noticed or not, conditions change within the forest, and these ongoing changes affect surrounding trees, water and sunlight distribution, and even the amount of material available to burn should a lightning strike or other cause spark a forest fire.
Similarly, whether measured, monitored or controlled — or not — temperature drives conditions in processing applications. Applying the proper amount of heat for the proper amount of time is critical for effecting the material changes sought at the root of many thermal processing applications. Of course, if you don’t want to be the one heard making a terrified shout, it is best to measure, monitor and control process temperature. In this issue of Process Heating, we have several articles that can help you do that.
In “Understanding Temperature Controller Technology,” Clayton Wilson, control instruments manager at Yokogawa Corporation of America, Newnan, Ga., explains temperature controllers, from simple to advanced, and shows how controllers act whenever the process variable deviates from the setpoint. As Wilson notes, each application should be examined in detail to determine which is the right controller to deploy for the process requirements.
One alternative to a stand-alone temperature controller is a PLC programmed to handle temperature monitoring and management duties. In “Use a PLC or Stand-Alone Temperature Control?” Jim Schroeder Sr., president of Seagate Control Systems Inc. in Toledo offers reasons for and against using a PLC for temperature control in your process. While Schroeder prefers one approach over the other (though you’ll have to read the article to find out which), he outlines the advantages and disadvantages of both approaches.
Temperature sensors are an essential part of an effective temperature control package. A failed temperature sensor can derail even the most sophisticated control system by reporting out false data. The controller responds to this false data by driving more (or less) heat into the process than is actually needed, and scrap product or worse is the result. “How to Reduce Warranty Costs Attributed to Temperature Sensors,” Brandon Coleman of Quality Thermistor Inc., Boise, Idaho, looks at sensor solutions on the market aimed specifically at challenging, high-cost-of-failure applications.