DVC6000~6200 Instrtn Manual Supplement Lock-In-Last-Strategy Feb 2011

Instruction Manual Supplement

DVC6000/DVC6200 Digital Valve Controllers

D103261X012

February 2011

Supplement to Fisherr FIELDVUEt DVC6000 or DVC6200 Digital Valve Controller Instruction Manuals Implementation of Lock‐in‐Last Strategy Many applications require a valve assembly to remain in the position it was prior to a specific control system failure (lock‐in‐last position). Functionality and safety can be designed into valve assemblies with FIELDVUE digital valve controllers by utilizing an array of accessories. The following paragraphs describe standard solutions for a number of generic lock‐in‐last applications with DVC6000 or DVC6200 digital valve controllers.

Note This instruction manual supplement is for use with HARTr communicating FIELDVUE DVC6000 or DVC6200 digital valve controllers only.

Lock‐in‐Last on Loss of Supply Pressure Once the supply pressure falls below a minimum value, the digital valve controller can no longer position a valve assembly; the valve will start to go to the actuator “at rest” position. The locking device senses this change and activates, preventing the remaining air from venting. The valve is “locked‐in” this new position.

Note The locked‐in valve position depends on the exhausting speed of the actuator.

Assemblies with Single‐Acting Actuators A Fisher 164A three‐way switching valve should be used for locking a single‐acting actuator in place on loss of supply pressure. Figure 1 is a schematic representing proper assembly layout. In normal operation, the digital valve controller output passes through the switching valve from port A to port B and on to the actuator.

www.Fisher.com