Principle Of Operation For 4195Ka Series Controllers; Overall Operation; Flapper Alignment - Fisher 4195 KB Series Instruction Manual

4195KA, KB, and KC Series

Flapper Alignment

Perform the process indicator zero and
span calibration procedure and, for con-
trollers with remote set point (suffix let-
ter M), the remote set point zero and
span calibration procedure before the
flapper alignment.
Flapper leveling screw numbers and adjustments are
shown in figure 3–3. Key number locations are shown
in figure 5–24.
Provide a means of measuring the controller output
pressure by connecting the controller output to a pres-
sure gauge (open-loop conditions must exist). Provide
a regulated supply pressure to the controller. Do not
exceed the normal operating pressure in table 1–6.
After performing the flapper alignment procedure, go
to the startup procedure.
1. 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 (suffix let-
ter M), adjust the remote set point pressure until the
set point indicator is at the mid-scale mark on the pro-
cess scale.
2. Apply process pressure equal to the mid-scale val-
ue of the process scale span. If pressure is not avail-
able to pressure the input element to the mid-scale
value, an alternate method is to disconnect link num-
ber 1 at the input element and tape the process point-
er at the mid-scale mark on the process scale. If the
controller has a capsular input element, note the hole
from which link number 1 was removed for proper re-
placement. This method should only be used if pres-
sure is not available to pressure the input element to
the mid-scale value.
3. Remove the two machine screws (key 6) and lift off
the proportional band indicator cover (key 36).
4. Adjust the proportional band between DIRECT and
REVERSE.
5. The controller output should be 9 0.10 psig (0.62
0.007 bar) for a 3 to 15 psig (0.2 to 1.0 bar) output or
18 0.2 psig (1.2 0.01 bar) for a 6 to 30 psig (0.4 to
2.0 bar) output. If not, adjust flapper leveling screw 2
(the screw nearest the nozzle) until the output is within
tolerance.
6. Set the proportional band to 30 percent DIRECT.
7. The controller output should be 9 0.25 psig (0.62
0.02 bar) or 18 0.5 psig (1.2 0.04 bar). If not, ad-
just flapper leveling screw 3 (the screw nearest the
nozzle).
3–6
Note
8. Set the proportional band to 30 percent REVERSE.
9. The controller output should be 9 0.25 psig (0.62
0.02 bar) or 18 0.5 psig (1.2 0.04 bar). If not, ad-
just flapper leveling screw 1 (the screw nearest the
nozzle).
10. Repeat steps 4 through 9 until the controller out-
put remains in tolerance without further leveling screw
adjustments.
11. If link 1 was disconnected, remove the tape and
reconnect link 1 to the input element.
12. Set the proportional band to 400 percent in the
desired controller action and replace the proportional
band indicator cover.
Principle of Operation for 4195KA Series
Controllers

Overall Operation

Refer to the schematic diagram in figure 3–4.
The input element is connected to the process pointer
and to the flapper by connecting links. As the process
pressure increases (in a direct-acting controller), the
flapper moves toward the nozzle, restricting flow
through the nozzle and increasing nozzle pressure.
When this occurs, relay action increases the output
pressure (delivery) of the controller. Output pressure is
fed back to the proportional bellows. The action of the
proportional bellows counteracts the flapper move-
ment that resulted from the process pressure change
and backs the flapper away from the nozzle until equi-
librium is reached.
Moving the set point indicator changes the distance
between the nozzle and flapper as does a change in
process pressure, except that when the set point is
changed, the nozzle moves with respect to the flapper.
The proportional band adjustment positions the nozzle
on the flapper. Increasing (widening) the proportional
band moves the nozzle to a position on the flapper
where less input and more feedback motion occurs,
which decreases the gain of the controller. Decreasing
(narrowing) the proportional band moves the nozzle
toward a position where more input and less feedback
motion occurs, which increases the gain. The control-
ler action is changed from direct to reverse by turning
the proportional band adjustment to position the
nozzle on the flapper quadrant to a point where the
direction of the flapper motion versus input motion is
reversed as shown in the flapper detail of figure 3–4.
With the controller in the reverse-acting mode, an in-
crease in process pressure causes a decrease in out-
put pressure.