Flowserve 3400IQ Digital Positioner - Manual (Page 13)

13
Logix 3400IQ Digital Positioner FCD LGENIM3401-00 – 06/06
flowserve.com
the stem moves, the Deviation begins to decrease. The control algorithm begins to reduce the spool
opening. This process continues until the Deviation goes to zero. At this point, the spool will be
back in its null or balanced position. Stem movement will stop and the desired stem position is now
achieved.
One important parameter has not been discussed to this point: Inner loop offset. Referring to Figure
2, a number called Inner loop offset is added to the output of the control algorithm. In order for the
spool to remain in its null or balanced position, the control algorithm must output a non-zero spool
command. This is the purpose of the Inner loop offset. The value of this number is equivalent to the
signal that must be sent to the spool position control to bring it to a null position with zero deviation.
This parameter is important for proper control and is optimized and set automatically during stroke
calibration.
Figure 3: Linear Mark One Control Valve Mounting
Logix 3400IQ
Positioner
Positioner
Bolts
Nut
Lock Washer
Nut
Follower Pin
Take-off Arm
Bolts
Stem Clamp
Bracket
Bolts
Bracket
Locknut
Washer
Follower
Arm
Nut
Metal Washers