Posts Tagged One Series
The following is an excerpt from “Digital switches with self-diagnostics can improve results and ease the implementation of safety systems” by Rick Frauton of United Electric, originally published in the September 2011 issue Pumps & Systems magazine. Rick is the product manager for UE’s One Series line of electronic pressure and temperature switches, and has been working with customers to identify applications where these switches can improve application and plant safety. Thanks, Rick, for being our guest blogger this week.
Years ago, most switches were blind mechanical devices actuated electromechanically or by pneumatics. They offered no indication of reliability, such as success or failure in response to a command. This lack of feedback was particularly worrisome in safety applications. The result could be catastrophic, should a malfunction occur in place of the proper response to a tripped pressure or temperature alarm.
Pressure switch deadband isn’t an unknown, but neither is it a known value when you take a new switch out of its shipping box.
Experienced users will tell you that three identical units of the same pressure switch can have three different deadbands. All three switches will trip at the same pressure setpoint, but reset at different points. To complicate matters, the deadband reset point changes with the pressure setpoint. And, they’ll also say, there’s no way to know, out of the box, what the deadband is without applying pressure and checking.
Who cares about deadband? Not everyone. The exact deadband reset point is critical in some applications, and inconsequential in others.
Why is getting a known, repeatable deadband such a challenge with conventional electromechanical pressure switches, and is there anything to be done about it?