Bourdon Tube Controller Calibration: Zero And Span Adjustment - Fisher 4195 KB Series Instruction Manual

Bourdon Tube Controller Calibration:
Zero and Span Adjustment
For routine zero and span calibration,
refer to the appropriate procedures in
section 3 or 4. Use the following mainte-
nance zero and span adjustment proce-
dure only if difficulty is encountered
with the routine procedure or if nonlin-
earity occurs.
Refer to figure 5–19 for location of adjustments and
figure 5–24 for key number locations.
Provide a means of applying process pressure to the
Bourdon tube and a regulated supply pressure ad-
justed to the normal operating pressure (see table
1–6). For a 4195KA Series controller, connect the con-
troller output to an accurate gauge. For 4195KB and
KC Series controllers, a gauge is not necessary and
the controller output connection may be plugged.
Any adjustment of the process pointer
span adjustment screw requires read-
justment of the process pointer zero ad-
justment screw. When checking the zero
and span adjustments, ensure that the
Bourdon tube does not contact the op-
tional travel stops if used (key 73 and
74).
1. Remove the two screws (key 6), and lift off the pro-
portional band indicator cover (key 36).
2. Set the proportional band adjustment between DI-
RECT and REVERSE.
3. Set the reset valve (4195KB and KC Series only) to
0.01 minutes per repeat.
4. Set the rate (4195KC Series only) to OFF.
5. For a controller with manual set point, move the set
point indicator to the mid-scale mark on the process
scale. For a controller with remote set point, adjust the
remote set point pressure until the set point indicator
is at the mid-scale mark on the process scale.
6. Apply process pressure equal to the mid-scale val-
ue of the process scale span.
7. The process pointer should be aligned with the
pointer subassembly as shown in figure 5–15. If not,
loosen the zero adjustment locking screw and adjust
the zero adjustment screw to align the process pointer
with the pointer subassembly. Tighten the zero adjust-
ment locking screw.
Note
Note
4195KA, KB, and KC Series
8. The process pointer should indicate mid-scale 3
percent of the process scale span. If not, loosen the
screws in link 1 and adjust the length so that the pro-
cess pointer points to the mid-scale mark on the pro-
cess scale. Tighten the screws.
9. Apply process pressure equal to the process scale
lower limit.
10. The process pointer should indicate the process
scale lower limit. If not, loosen the zero adjustment
locking screw and adjust the zero adjustment screw
until the process pointer indicates the lower limit.
Tighten the zero adjustment locking screw.
11. Apply process pressure equal to the process
scale upper limit.
12. The pointer should indicate the process scale up-
per limit. If not, proceed as follows:
a. If the pointer indicates less than the process
scale upper limit, rotate the pointer span adjust-
ment clockwise to increase the span. Adjust the
span adjustment screw to correct for half of the
error.
b. If the pointer indicates greater than the process
scale upper limit, rotate the pointer span adjust-
ment counterclockwise to decrease the span. Ad-
just the span adjustment screw to correct for half of
the error.
13. Repeat steps 9 through 12 until the zero and span
indications are within 1 percent of the scale limits
with no further adjustment. If proper span is achieved,
proceed to step 15. If the span adjustment screw is
adjusted to its limit and the span is still too short or too
long, proceed with step 14.
14. Within the process pointer subassembly, there are
three holes for the connection of link 1. Use procedure
(a.) or (b.) below to make the coarse span adjustment
with link 1.
a. If the span is short (process pointer indication is
less than the process scale upper limit), disconnect
link 1 from the process pointer subassembly and
move the link to the lowest hole (the hole nearest
the pointer pivot). Return to step 9.
b. If the span is long, (process pointer indication is
greater than the process scale upper limit), discon-
nect link 1 from the process pointer subassembly
and move the link to the highest hole (hole further-
most from the pointer pivot), and return to step 9.
15. Apply process pressure equal to the mid-scale
value of the process scale span. The process pointer
should indicate mid-scale 2 percent of the process
scale span. If the process pointer error is 2 percent
or less, proceed to step 17. If the process pointer error
is greater than 2 percent, loosen the two Bourdon
5–21