When considering upgrading the electro-mechanical switches that have been in service for many years, the task can seem daunting. These 2-wire alarm and shutdown devices have served the plant well for many years. Many of the switches have been in service for more than 15 years without failure. But these switches are blind (lack self diagnostics) and are difficult to calibrate.
Process transmitters seem like the obvious choice to replace these switches. Transmitters include diagnostics and don’t require calibration inspections as often as their mechanical brethren. But replacing a mechanical switch with a transmitter is overkill. The unit cost of a mechanical switch versus a process transmitter has a differential of 1.5 – 2 times the original cost of the switch. On top of that, there is wiring, analog inputs and control schemes to consider. And because the plant was built in the 1970s, there are switches everywhere!
Is there an alternative? One that provides easy adjustability, self diagnostics and can operate using the existing plant wiring and control scheme? Yes! Consider replacing your electro-mechanical switches with a new breed of switch – the One Series 2-Wire electronic switch. The One Series provides IAWTM self diagnostics, configurable set point and deadband, digital process display and operates on the same 2 wires and control scheme as the old mechanical switch being replaced.
By Rick Frauton ,Senior Product Marketing Manager at United Electric Controls