Posts Tagged pressure switches
Chemical seals and fills are often necessary to protect your process instrumentation from harm. But the wait for a custom gauge-and-seal, switch-and-seal, or transmitter-and-seal combination could be an issue, keeping your process offline for longer than necessary, or costing a premium for quick delivery.
We’ve removed the potential for downtime and rush charges with our WIKA-certified assembly station, and improved stock of most popular transmitters, switches, gauges, diaphragm seals, and fill fluids. Lesman customers can experience next-day delivery on custom assemblies from in-stock instrumentation.
Eight problems with outdated, electromechanical switches and eight solutions that will come with a digital upgrade to your plant.
The Problem: Unless tested on a regular basis, there is no way to determine when a problem exists. With mechanical switches, the only way to diagnose a problem is to remove the switch, leaving the control or safety function
Solution: Newer digital switches have an LCD screen that shows local process variable measurements and integrated internal diagnostics directly on the screen. You can easily monitor the health of the device at a glance, without having to remove the switch from operation.
The Problem: Mechanical switches require careful adjustments for reaching desired setpoints. Additionally, once these adjustments are made, settings
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?