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4194A, B, and C Series
12. If necessary, perform the process indicator zero
and span calibration procedure in this section. Other-
wise, perform the flapper alignment procedure in this
section.
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 5-21.
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 1-4.
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 on the process
scale.
2. Apply process differential pressure equal to the
mid-scale value of the process scale span. If pressure
is not available to pressure the input element to the
mid-scale value, an alternate method is to disconnect
link number 1 at the input element and tape the pro-
cess pointer at the mid-scale mark of the process
scale. Note the hole from which link number 1 was
removed for proper replacement. This method should
only be used if pressure 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. Set 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-
3–6
Note
just flapper leveling screw 3 (the screw nearest the
nozzle).
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
adjustment.
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 4194A 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
differential pressure increases (in a direct-acting con-
troller), the flapper moves toward the nozzle, restrict-
ing 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 flap-
per movement that resulted from the process differen-
tial pressure change and backs the flapper away from
the nozzle until equilibrium 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 differential pressure causes a de-
crease in output pressure.
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