Replacing The Links; Replacing Link 1; Replacing Link 2 - Fisher 4194B Series Instruction Manual

LINK 5 LINK 1
LINK 2
LINEARITY
ADJUSTMENT
LINK 2 ADJUSTMENT
SCREW
W4769 / IL
Figure 5-13. Link Locations

Replacing the Links

This section describes the separate replacement of
five links in the controller. Figure 5-13 shows the loca-
tion of each link. To clarify the location of each link, the
links are numbered as follows:
Link 1 connects the short pivot clevis assembly
and the process pointer
Link 2 connects the process pointer and the flap-
per assembly (key 11)
Link 3 connects the set point indicator and the
set point beam assembly (key 23)
Link 4 (key 65) connects the flapper assembly
and the bellows bracket (key 31)
Link 5 (key 88 in figure 5-23) connects the short
pivot clevis assembly (key 89) and the long pivot clevis
assembly (key 78).

Replacing Link 1

1. Remove the two screws (key 6), and lift off the pro-
portional band indicator cover (key 36).
2. Note the hole position of link 1 and disconnect the
link from the short pivot clevis assembly and from the
process pointer. Remove the link.
3. Attach the replacement link in the same holes
noted in step 2 to the process pointer and the short
pivot clevis assembly. If you do not know in which hole
in the process pointer the link was connected, place it
in the middle hole. If during the process pointer zero
and span calibration, the pointer will not travel the full
scale, even after full span adjustment, move the link to
the bottom hole (the hole nearest the pointer pivot). If
the process pointer has too much travel, move the link
LINK 4 LINK 4 ADJUSTMENT
LINK 3
LINK 3 ADJUSTMENT
4194A, B, and C Series
to the top hole (the hole furthest from the pointer piv-
ot).
4. Move the set point indicator, manually or with re-
mote set point pressure, to the mid-scale mark on the
process scale and set the proportional band between
DIRECT and REVERSE.
5. The process pointer should be aligned with the
pointer subassembly as shown in figure 5-14. If not,
loosen the zero adjustment locking screw and adjust
the process pointer zero adjustment to align the pro-
cess pointer and pointer subassembly. Tighten the
zero adjustment locking screw.
6. Apply process differential pressure equal to the
mid-scale value of the process scale span. The pro-
cess pointer should indicate mid-scale 3 percent of
the process scale span. If not, loosen the screw in link
1 or link 5, and move the pointer to the mid-scale mark
on the process scale. Tighten the screw.
7. Perform the controller calibration procedures and, if
necessary, the appropriate remote set point calibration
procedure in section 3 or 4.

Replacing Link 2

1. Remove the two screws (key 6), and lift off the pro-
portional band indicator cover (key 36).
2. Disconnect link 2 from the process pointer and
from the flapper assembly (key 11). Remove the link.
3. Install the replacement link with the screw head
nearest the process pointer as shown in figure 5-13.
Connect the link to the process pointer only.
4. The process pointer should be aligned with the
pointer subassembly as shown in figure 5-14. If not,
loosen the zero adjustment locking screw and adjust
the process pointer zero adjustment to align the point-
er with the process pointer subassembly. Tighten the
zero adjustment locking screw.
5. Move the set point indicator, manually or with re-
mote set point pressure, to the process scale lower
limit and set the proportional band to 5 percent RE-
VERSE. The nozzle should not be touching the flap-
per. If it is, adjust flapper leveling screw 1 (the screw
nearest the nozzle) until clearance is obtained.
6. Note the hole position and disconnect link 1 from
the short pivot clevis assembly. Manually position the
process pointer to the process scale upper limit and
tape the process pointer in this position.
7. Adjust the length of link 2 (by turning the adjusting
screw clockwise to increase the length or counter-
clockwise to decrease the length) so that the pin on
the end of the link is approximately one-half of its di-
ameter short of aligning with the hole in the flapper
assembly as shown in figure 5-11. This adjustment
provides the proper tension on the link to eliminate lost
motion.
5–17