External Feedback Operation - Fisher 4195 KB Series Instruction Manual

4195KA, KB, and KC Series
RESET
VALVE
RESET PROPORTIONAL
BELLOWS BELLOWS
19A5000–A
A3237-2 / IL
Figure 4–7. Reset-Rate Schematic
Remote Set Point (suffix letter M)
Operation
The capability to adjust the controller set point from a
remote location is available with all 4195KB and KC
Series controllers. This option is designated by the
letter M in the type number.
A control pressure is applied to the capsular element
within the remote set point assembly. The expansion
and contraction of the capsule moves the set point
indicator via connecting linkage. Increasing the control
pressure to the capsule increases the set point setting
and decreasing the control pressure reduces the set
point setting.
4–12
RELAY OUTPUT
PRESSURE
RATE
VALVE
GAIN
LIMITER
Auto/Manual Station (suffix letter E)
Operation
A controller with the auto/manual station (designated
by the suffix letter E in the type number) has piping on
the output side of the relay as shown in figure 4–8.
Supply pressure to the relay is also applied to the
manual loader. The manual loader, functioning as a
regulator, applies pressure to one side of the plastic
tube and to the auto/manual switch. Output pressure
from the relay registers on the other side of the plastic
tube as well as in the auto/manual switch.
When the auto/manual switch is in the MANUAL posi-
tion, the manual loader output is channeled through
the auto/manual switch and becomes the controller
output. When the auto/manual switch is in the AUTO
position, the relay output is channeled through the
switch to become the controller output.
Before the auto/manual switch is operated, the relay
output must equal the manual loader output to avoid
bumping the process. Adjusting the set point varies
the pressure on the left-hand side of the plastic tube.
Adjusting the manual loader knob varies the pressure
on the right-hand side. When the pressures are equal,
the metal ball is centered in the tube and it is held in
place by a small magnet. A pressure imbalance forces
the ball to one end of the tube where it forms a seal,
blocking air flow through the tube.

External Feedback Operation

External feedback is available for all 4195KB Series
controllers. Controllers with this option have an exter-
nal connection on the bottom of the controller case as
shown in figure 2–5. This connection breaks the posi-
tive feedback (reset) loop inside the controller and
brings it outside as shown in figure 4–9. The connec-
tion allows the positive feedback loops of two control-
lers (primary and secondary) to be tied together when
the controllers are used in an override application.
When connected, the secondary controller tracks the
primary controller, minimizing reset windup.