Logix 3400MD Digital Positioner FCD LGENIM3404-00 – 9/09
10
the top of the actuator. This new pressure differential causes the stem
to start moving towards the desired position of 75 percent. As 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.
5
Mounting and Installation
5.1 Mounting to Valtek Linear
Mark One Valves
To mount a Logix 3400MD
positioner to a Valtek linear Mark One valve,
refer to Figure 3 and proceed as outlined below. The following tools are
required:
•
9
⁄
16
" open-end wrench (or 1/2" for spud sizes 2.88 and smaller)
•
7
⁄
16
" box wrench
•
3
⁄
8
" open-end wrench
1. Remove washer and nut from follower pin assembly. Insert pin into
the appropriate hole in follower arm, based on stroke length. The
stroke lengths are stamped next to their corresponding holes in the
follower arms. Make sure the unthreaded end of the pin is on the
stamped side of the arm. Reinstall lock washer and tighten nut to
complete follower arm assembly.
2. Slide the double-D slot in the follower arm assembly over the flats
on the position feedback shaft in the back of the positioner. Make
sure the arm is pointing toward the customer interface side of the
positioner. Slide lock washer over the threads on the shaft and
tighten down the nut.
3. Align the bracket with the three outer mounting holes on the
positioner. Fasten with 1/4" bolts.
4. Screw one mounting bolt into the hole on the yoke mounting pad
nearest the cylinder. Stop when the bolt is approximately
3
⁄
16
" from
being flush with mounting pad.
5. Slip the large end of the teardrop shaped mounting hole in the back
of the positioner/bracket assembly over the mounting bolt. Slide
the small end of the teardrop under the mounting bolt and align the
lower mounting hole.
6. Insert the lower mounting bolt and tighten the bolting.
7. Position the take-off arm mounting slot against the stem clamp
mounting pad. Apply Loctite 222 to the take-off arm bolting and
insert through washers into stem clamp. Leave bolts loose.
8. Slide the appropriate pin slot of the take-off arm, based on stroke
length, over the follower arm pin. The appropriate stroke lengths
are stamped by each pin slot.
9. Center the take-off arm on the rolling sleeve of the follower pin.
10. Align the take-off arm with the top plane of the stem clamp and
tighten bolting. Torque to 120 in-lb.
NOTE:
If mounted properly, the follower arm should be horizontal
when the valve is at 50% stroke and should move approximately
±30° from horizontal over the full stroke of the valve. If mounted
incorrectly, a stroke calibration error will occur and the indicator
lights will blink a YRYR or YRRY code indicating the position
sensor has gone out of range on one end of travel. Reposition the
feedback linkage or rotate the position sensor to correct the error.
5.2 Mounting to Standard Valtek
Rotary Valves
(See Figure 4)
The standard rotary mounting applies to Valtek valve/actuator assem-
blies that do not have mounted volume tanks or handwheels. The
standard mounting uses a linkage directly coupled to the valve shaft.
This linkage has been designed to allow for minimal misalignment
between the positioner and the actuator. The tools required for the
following procedure are:
•
5
⁄
32
" Allen wrench
• 1/2" open-end wrench
•
7
⁄
16
" open-end wrench
•
3
⁄
8
" socket with extension
•
3
⁄
16
" nutdriver
1. Fasten the spline lever adapter to the splined lever using two 6 x 1/2"
self-tapping screws.
2. Slide the take-off arm assembly onto the spline lever adapter shaft.
Insert the screw with star washer through the take-off arm and
add the second star washer and nut. Tighten nut with socket so
arm is lightly snug on the shaft but still able to rotate. This will be
tightened after linkage is correctly oriented.
