Replacing The Process Tubing; Capsular Element Maintenance Calibration; Precalibration Procedures; Aligning The Drive Bracket Assembly - Fisher 4194B Series Instruction Manual

4194A, B, and C Series
See figure 5-18. The adjustment arm of
the long pivot clevis assembly is con-
nected to a shaft that turns on bushings
at each end of the shaft. In the next
step, position the shaft so that both
bushings ''float'' inside the bearings
and do not rest against the end of either
bearing.
5. Before tightening the drive flexure cap screws (key
12), hold the pivot shaft in the middle of the bushing
end play. Be sure neither bushing is resting against
the inside end of either bearing. Tighten the drive flex-
ure cap screws to hold the pivot shaft in position. Take
care not to kink or twist the flexure when tightening the
screws.
6. Perform the capsular element maintenance calibra-
tion procedures in this section. Perform the controller
calibration procedures and, if necessary, the appropri-
ate remote set point calibration procedures in section
3 or 4.

Replacing the Process Tubing

1. Remove process pressure from the controller.
2. Using two open-end 5/16-inch wrenches, discon-
nect the process tubing (keys 91 or 92) at the pedestal
assembly (key 81) and at the bottom of the controller
case. Remove the tubing.
3. Install the replacement tubing, and tighten all con-
nections. Check for leaks.
4. Perform the controller calibration procedures and, if
necessary, the appropriate remote set point calibration
procedure in section 3 or 4.
Capsular Element Maintenance
Calibration

Precalibration Procedures

1. Remove the two machine screws (key 6) and lift off
the proportional band cover (key 36).
2. Set the proportional band between DIRECT and
REVERSE.
3. Remove the two screws (key 103) and remove the
tie bar (key 97) from the capsular element assembly.

Aligning the Drive Bracket Assembly

Refer to figures 5-17 and 5-23.
1. With an Allen wrench, loosen the set screw in the
hex nut (key 86) of the drive bracket assembly (key
84).
5–22
Note 2. Loosen the screw (key 98) that holds the guide
flexure to the tab on the mounting plate (key 77). The
guide flexure location is shown in figure 5-17.
3. Apply process differential pressure equal to 75 per-
cent of the capsular element range.
4. Slide the drive bracket assembly (key 84) along the
diaphragm capsule extension (key 82) until the guide
flexure is aligned with the center of the long pivot cle-
vis assembly (key 78).
5. Tighten the machine screw (key 98) and the set
screw in the hex nut to fasten the drive bracket as-
sembly in that position.

Setting the Travel Stops

1. Loosen the set screw in the travel stop nut (key
86).
Make sure the loose travel stop nut does
not bind on the diaphragm capsule ex-
tension when pressurizing the capsules.
Damage to the capsules may result.
2. For Full span stop—Apply process differential
pressure equal to 5 percent greater than the capsular
element range.
Loosen the screws (key 139) that secure the travel
stop (key 83) to the mounting plate (key 77). Slide the
travel stop until it is just touching the end of the cap-
sule stack. Tighten the travel stop mounting screws to
lock it into position. Decrease the input pressure to
100 percent of the capsular element range and make
sure the capsule stack is not contacting the travel stop
(key 83).
3. Zero stop—Adjust process differential pressure
input to 0 percent of the capsular element range.
Slide the travel stop nut (key 86), along the diaphragm
capsule extension (key 82) until it is approximately
1/64-inch (0.4 mm) away from the travel stop. Tighten
the set screw to lock the travel stop nut in position.

Aligning the Linkage

Refer to figure 5-17 and 5-23.
1. Adjust the process differential pressure input to 75
percent of the capsular element range. The drive flex-
ure (key 79) should be straight and horizontal. If it is
not, proceed as follows:
a. Loosen the screw on the pivot adjustment arm
on the long pivot clevis assembly (key 78) and the
two screws mounting the drive flexure.
b. Adjust the length of the pivot adjustment arm so
that the drive flexure is parallel to the centerline of
Note