The Case for Electronic Switches in a Digitized Plant
Electro-mechanical switches were once ubiquitous in industrial plants. With the advancement of instrumentation technology, the apparent limitations of these switches has become more obvious over time.
For example, plant operators demanded greater accuracy and repeat ability from process monitoring/control instrumentation, something which could not be fulfilled by mechanically-operated switches. The same end users also gravitated towards instrumentation that could provide a level of self-diagnostics that could self-validate device health beyond simple on-off switch control. As the industrial world adopted a more data-driven approach to their operations and maintenance, switches were gradually replaced with transmitter technology in many industrial plants across the world. From a plant operator’s perspective, switches are currently deemed as antiquated technology, with no clear present-day relevance and advantages.
But is that really true?
In the critical domain of safety, alarm and emergency shutdown, switch technology continues to provide an extremely reliable, cost-effective, simple and fast-acting control of process equipment. For instance, when connected directly to the final control element, switches can effect an emergency shutdown within a response time as little as 5 milliseconds. A transmitter would take 20 times longer (i.e at least 100 milliseconds). Moreover, where there is an unexpected disruption of power in a segment of the plant, switches can continue to perform its function of emergency shutdown uninterrupted, as they do not require power to operate, unlike the loop-powered transmitters. In such a scenario, switches often become the last layer of instrumentation defense until power is restored in the facility.
Switches have their advantages, as do transmitters. From a user standpoint, the key is to deploy a diversification of technologies to avoid common modes of failure. When used in combination (e.g. in a redundant 1:1 arrangement), the timeless benefits of switch technology AND the cutting-edge advantages of transmitters can certainly help improve the overall safety level of the plant, but this comes at costly expense. Installing expensive transmitters mean higher capital expenditures, and this has left plant managers desiring for a more economical but equally effective alternative.
This void in the market resulted in the development of smart electronic switches.
Over the years, smart electronic switches have carved out a niche for themselves by integrating the simplicity of a snap-acting switch with the diagnostic capabilities of transmitter technology, all in one device. While these devices do not possess the high accuracy of a transmitter (e.g. 0.05%), they are designed to provide both an analog output and switching capability, all at an accuracy of 0.1%. Some of these electronic switches also come integrated with a digital display, just like a gauge. Electronic switches are gradually emerging as ideal mechanical switch upgrade alternatives to costly transmitters that can sometimes be a technology overkill for a simple application that would not require a high process monitoring accuracy.
As aging plants across the world upgrade and digitize their technology, these electronic switches with its intelligent diagnostics can help plants enhance their process data capture and reporting, all at third to half the cost of a transmitter.
From an operator’s standpoint, there are many customer benefits that such a smart electronic switch can bring (e.g. drop-in-replacement, on-board diagnostics, vibration-resistant solid state relay).
About the Author: Julian Yeo,Strategic Marketing Manager.
Julian Yeo is a Strategic Marketing Manager for United Electric Controls and is responsible for international marketing and business development. Prior to this, he was product manager for UE’s gas detection and electromechanical switch product lines. Julian has been with UE for 7 years.