Instruction Manual
D200156X012
4194HA, HB, HC Controllers
July 2018
35
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 position, the output of the manual loader is channeled through the
auto/manual switch and becomes the output of the controller. When the auto/manual switch is in the AUTO position,
the output of the relay is channeled through the switch to become the output of the controller.
Figure 4‐5. Schematic of Auto/Manual Option
AUTOMATIC
POSITION
OUTPUT PRESSURE
TO FINAL CONTROL
ELEMENT
SUPPLY PRESSURE
RELAY
AUTO/MANUAL
SWITCH
MANUAL LOADER
MANUAL
LOADER
KNOB
MANUAL
POSITION
AUTO/MANUAL
SWITCH
OUTPUT PRESSURE
TO FINAL CONTROL
ELEMENT
PLASTIC TUBE
METAL BALL
RELAY OUTPUT PRESSURE
SUPPLY PRESSURE
MANUAL LOADER OUTPUT PRESSURE
48A5230‐A
A2999‐1
Before the auto/manual switch is operated, the output of the relay must equal the output of the manual loader 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 of the plastic tube. When the pressures
are equal, the metal ball is centered in the tube and it is held in place by a small magnet. Pressure imbalance forces the
ball to one end of the tube where it forms a seal, blocking air flow through the tube.
External Feedback Option
External feedback is available for all 4194HB controllers. Controllers with this option have an external connection on
the bottom of the controller case (figure 2‐2). This connection breaks the positive feedback (reset) loop inside the
controller and brings it outside (figure 4‐6).
The connection allows the positive feedback loops of two controllers (primary and secondary) to be tied together
when the controllers are used in an override application. When connected, the secondary controller reset pressure
tracks the primary controller output pressure, minimizing reset windup in the secondary controller.