A recent discussion at control.com, an online community for automation professionals, was started by an instrument engineer who asked for advice on choosing between software-based level transmitters or mechanically triggered level switches.
The engineer, a Mr. Hasseli, wanted to determine the best solution for producing a reliable level signal. At first, discussion seemed split; one poster favored transmitters as they are becoming increasingly affordable and typically offer more detailed information about the state of contained fluids, while another championed switches as being easier to maintain and calibrate.
Then forum moderator and International Society of Automation Life Fellow Walt Boyes weighed in, saying “For every instance of an LS working better than an LT, I can give you the opposite.” Other experienced posters agreed, advocating a unified approach to sensing to ensure safety.
“Having both instruments mounted on the vessel offers increased LOPA should functionality fail on one of instruments,” said one commenter.
“Using a level transmitter provides you with more information on the tank contents and more flexibility with your control… [but] I prefer to have a level switch installed as a secondary backup to prevent overfills,” seconded the vice president of a control systems implementation company.
We’re inclined to agree. Safety should always be the first concern, and diversifying sensing instrumentation greatly reduces the potential for catastrophic equipment failure.