Fisher IM Supplement: FIELDVUE DVC6200 - Implementation of Lock-in-Last Strategy Manuals & Guides

Instruction Manual Supplement

D103261X012

DVC6200 Digital Valve Controllers

February 2020

Implementation of Lock‐in‐Last Strategy

Supplement to Fisher™ FIELDVUE™ DVC6200 Digital Valve
Controller Instruction Manuals

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 HART

Note

This instruction manual supplement also pertains to FELDVUE DVC6000 digital valve controllers; refer to the appropriate DVC6200
or DVC6000 document below, available from your Emerson sales office or at Fisher.com.

 DVC6200 Series Digital Valve Controller Quick Start Guide (D103556X012)

D
D DVC6200 HW2 Digital Valve Controller Instruction Manual (D103605X012)

D

 DVC6200 HW1 Digital Valve Controller Instruction Manual (D103409X012)

D DVC6000 Digital Valve Controllers Instruction Manual (D102794X012)

Other related documents include:

D

 Fisher 377 Trip Valve Instruction Manaul (D200319X012)

D 167D, 167DA, 167DS and 167DAS Switching Valves Installation Guide (D103234X014)
D 167D, 167DA, 167DS and 167DAS Switching Valves Instruction Manual (D103234X012)

®

Communicating DVC6200 digital valve controllers.

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 167DA 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.

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DVC6200 Digital Valve Controllers

Instruction Manual Supplement

February 2020

Figure 1. Lock‐in‐Last on Loss of Supply Pressure for an Assembly with a Single‐Acting Actuator

FISHER 167DA THREE‐WAY
SWITCHING VALVE

D

D103261X012

DIGITAL

VALVE

CONTROLLER

B

OUTPUT
SUPPLY

A

C

AIR
SUPPLY

FISHER 67CFR
FILTER/REGULATOR

In a fail condition, the pressure at port D is below the switching valve's set point, causing the switching valve to trip.
This closes port B, which locks the pressure in the actuator. Port C is plugged so the digital valve controller output will
not exhaust to the atmosphere.

Assemblies with Double‐Acting Actuators

Similar to the locking strategy used with single‐acting actuators, the locking strategy with double‐acting actuators
also uses a valve for locking supply pressure in the actuator. For assemblies with double‐acting actuators, a Fisher 377L
trip valve is used as the locking device. The 377L trip valve has two output ports for locking pressure on both sides of a
double‐acting actuator. Figure 2 is a schematic representing proper assembly layout.

Figure 2. Lock‐in‐Last on Loss of Supply Pressure for an Assembly with a Double‐Acting Actuator

FISHER 377L TRIP VALVE

INPUT

D

A

E

B

F

C

FISHER 67D
REGULATOR

DIGITAL

VALVE

CONTROLLER

2

OUTPUT
SUPPLY
OUTPUT

AIR
SUPPLY

Instruction Manual Supplement

D103261X012

DVC6200 Digital Valve Controllers

February 2020

Connection of the digital valve controller output to a double‐acting actuator determines the action of the actuator.
Figure 2 shows the digital valve controller providing lower cylinder pressure through ports D and E, and upper cylinder
pressure through ports A and B. When the supply pressure falls below the set point of the trip valve, the trip valve
closes ports D and A and connects port B to C and port E to F. Because C and F are plugged, the control valve is locked
in place by locking pressure on both sides of the actuator piston. The assembly returns to normal operation once
supply pressure is restored at the trip valve INPUT port.

Note

Double‐acting actuators with a 377L trip valve require a Fisher 67D or MR95H regulator. Regulators with smaller flow capacities
may cause the trip valve to cycle (lock and unlock repeatedly) due to air flow demand as the assembly attempts to reset. Use a
Fisher 252 or 262C pilot filter to filter supply air.

Both the 167DA switching valve and the 377L trip valve have a deadband that must be overcome. The switching valve must be
calibrated to reset upon restoration of adequate supply pressure to the regulator. The 377L trip valve has only one spring
selection. However, for minimal deadband, the lightest appropriate spring should be selected for the 167DA switching valve.

Lock‐in‐Last Using Solenoid Valves

Solenoid valves are used with valve assemblies in many ways. Their electrical control can be utilized in combination
with switches and controller logic to perform a number of functions.

Note

Solenoid valves placed between the output of a DVC6200 digital valve controller and the input to an actuator require a minimum
C

of 0.49. Greater restrictions can affect the response of the assembly. An example of an appropriate three‐way solenoid valve for

v

use with the digital valve controller is the ASCO

Assemblies with Single‐Acting Actuators

A three‐way universal solenoid valve can be placed between the digital valve controller output and the actuator input.
Switching the valve assembly from an unlocked state to a locked state is controlled by switching power on and off to
the solenoid valve. Figure 3 depicts proper assembly layout.

Under normal operating conditions the solenoid is energized and supply air flows from the digital valve controller
output to the actuator input. In the fail state, power is removed from the solenoid causing the solenoid valve to close,
locking air pressure in the actuator. Port 1 of the solenoid valve is plugged, preventing actuator air pressure from
exhausting to the atmosphere.

™ 8327 Series solenoid valve from ASCO Valve, Inc.

3