Emerson has introduced the Fisher FIELDVUE 4400 position transmitter for use in critical isolation valve applications, including chemical reactor feed shutdown, pressure swing absorption, mineral pressure oxidation isolation, steam generator shutdown, and others.
Isolation valves are typically outfitted with open and closed limit switches that provide valve position feedback. Unfortunately, the on/off nature of the switches severely limits the ability to diagnose valve performance, so a degrading valve will go unnoticed until it fails outright. Such a failure can have serious process implications, and it can pose safety risks as well.
HART-enabled FIELDVUE 4400 valve position transmitters offer a cost-effective solution to address this and other issues. The transmitter is very easy to calibrate, and it incorporates a proven, linkage-less design. As compared to limit switches, it provides much higher reliability, along with valve diagnostics and Safety Integrity Level (SIL) 2 capabilities—the latter often required in critical isolation valve applications. The position transmitter also includes limit switch outputs, so it can be retrofitted into an existing on/off switch circuit, while also taking advantage of the valve position information.
The position transmitter offers an inherent advantage over limit switches since it provides a continuous position indication throughout the valve stroke to a host, such as a distributed control or an asset management system, via HART. If a valve is failing to reach end-of-stroke or hanging/sticking during transition, this is immediately apparent from the position signal. Also, a failure of the transmitter itself is instantly detected as the continuous signal is lost, so it can be flagged for repair.