Fisher 4194B Series Instruction Manual page 30

4194A, B, and C Series
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
4–12
RESET
VALVE
RESET PROPORTIONAL
BELLOWS BELLOWS
19A5000–A
A3237–2 / IL
Figure 4-7. Reset-Rate Schematic
RELAY OUTPUT
PRESSURE
RATE
VALVE
GAIN
LIMITER
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 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.