Two posts, Valve Travel Control-Pressure Fallback and More on Digital Valve Controller Travel to Pressure Fallback Mode proved to be very popular with the readers of this blog. These posts, featuring Emerson’s Riyaz Ali shared how the Fisher DVC6200 digital valve controller can detect position feedback problems and automatically revert to current-to-pressure (I/P) transducer mode to keep the valve fully operational.
The information contained in these posts have been formalized into an instruction manual supplement for the DVC6200 HW2 digital valve controller. The supplement, Travel Control/Pressure Fallback Fisher FIELDVUE DVC6200 HW2 Digital Valve Controller opens:
Valve position feedback is very important to control valve performance. The DVC6200 HW2 digital valve controller provides a unique feature to detect position feedback issues and automatically revert from travel control to pressure control (I/P transducer mode) to keep the valve operational. This can help avoid costly unplanned spurious trips that can affect plant operation.
A caveat for the instrument level AD, PD, or ODV is that it:
…can fallback into pressure control mode only if the unit is direct- or reverse-acting single output. The pressure fallback feature will not work on dual outputs that are required for double-acting piston actuators.
This fallback from travel control to pressure control is based on these parameter settings:
- Fallback on Sensor Failure—When the instrument detects a travel sensor failure it will fall back into pressure control mode. The instrument will disregard the travel feedback and control based on output pressure.
- Fallback on Sensor Failure or Deviation—Pressure fallback will occur when the instrument detects a travel sensor failure or if the configured deviation between travel target and actual travel have exceeded the travel deviation time.
- Fallback Recovery—If the instrument has fallen into pressure control and the feedback problem is resolved, recovery to travel control can occur automatically or with manual intervention. To return to travel control when Manual Recovery is selected, change the Fallback Recovery to Auto Recovery, and then back to Manual Recovery.
Read the instruction manual supplement for the DVC6200 digital valve controller for more on choosing control modes, advantages of travel control/pressure feedback, and other information to improve the performance of your control valves. Visit the Digital Valve Controllers section on Emerson.com for more on how these controllers help you optimize control for more efficient and reliable operations.
You can also connect and interact with other control valve experts in the Valves, Actuators & Regulators group in the Emerson Exchange 365 community.