A great source for fundamentals in process automation is the International Society of Automation (ISA)‘s InTech Focus electronic periodical. This series of electronic magazines:
…focuses on the fundamentals of essential automation components, such as instrumentation, final control elements, networks, drives, and more. Readers will learn how to choose them, apply them, calibrate them, and optimize their contribution to efficient operations.
The March 2019 edition focused on Flow & Level measurement and the May 2019 edition on Temperature & Pressure measurement. Authors from many of the automation suppliers contributed to each of these editions. In the Temperature & Pressure edition, Emerson’s Greg McMillan and Mark Menezes each contributed an article.
Greg McMillan
Temperature measurement and control is a critical condition for a wide variety of industrial processes, from combustion or calcination in the process industries to chilled water or cooling tower applications for environmental control, and many more. Learn how different types of temperature sensors operate, how errors can be eliminated, and how plant performance can be improved.
Mark Menezes
Field devices, especially pressure measurement installations, can experience maintenance problems and erratic performance in cold weather. Effective product design, installation and maintenance procedures can minimize these issues.
Greg opened highlighting the importance of controlled temperatures in many types of applications. It:
…is a critical condition for reaction, fermentation, combustion, drying, calcination, crystallization, extrusion, or degradation rate and is an inference of a column tray concentration in the process industries.
Unlike faster response times with other measurements such as pressure, level and flow:
…the slowness of the response of the temperature process is the biggest source of problems and opportunities for tight temperature control. The slowness makes it difficult to tune the controller because the persistence and patience required to obtain a good open- or closed-loop test exceeds the capability of most humans.
Greg highlights the various temperature measurement technologies and ways to install to get more accurate, reliable and long-lasting measurements. I barely scratched the surface so make sure to read Greg’s article.
In Mark’s article, he opens describing how many in cold climates know how cars can be difficult to start and operate in cold conditions. Electronics in measurement devices can operate differently at different temperature ranges. Given these differences:
…most sensor technologies require some degree of thermal compensation in all circumstances.
For pressure measurement devices, impulse lines, “…those small tubes (capillaries) leading from the process penetration point to a pressure instrument carrying either the process liquid or some other filler material to transmit pressure to the sensor…”, can freeze.
They:
…have to be filled with something, either gas or liquid, and are described as dry legs or wet legs, respectively. If the instrument is on a steam line, the fluid is probably condensate.
For some plants:
…where temperatures can swing from -40 to 38 ºC (-40 to 100 ºF) over the span of a year, the heat dissipation characteristics of impulse lines change drastically with temperature.
Read the article for solutions for both extreme cold and heat conditions to still be able to provide accurate and reliable measurements.
Visit the Temperature Measurement and Pressure Measurement sections on Emerson.com for more educational information on selecting, installing and operating these critical measurements for optimal performance. You can also connect and interact with other temperature and pressure measurement experts in the Measurement Instrumentation group in the Emerson Exchange 365 community and/or at the September 23-27 Emerson Exchange conference in Nashville.
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