Ametek PMT 40, Manual

Page: 9 / 49

User Manual
4
PROPOR RESET CONTROLLER
(Fig. 10)
The function of the reset action is to eliminate
the proportional offset between the measuring
process and the setpoint and to accomplish this
in the shortest possible time without creating
instability in the proportional control action. The
reset feedback is similar in appearance to the rate
feedback except that the output pressure is also
applied to the inside of the capsule. When the
reset valve is shut, the reset action is eliminated
and the controller operates as a proportional
instrument. When the reset valve is set to the
proper restriction the reset restriction and reset
chamber form a resistance-capacity network
which at first delays the balance across the
capsule but in a definite time period produces
equilibrium and restores the process to the set
point.
In Fig. 10, with the nozzle and proportional dial in
the positions shown, the proportional and reset
controller will be reverse acting.
PROCESS CONNECTION PROCESS POINTER (BLACK)
PROCESS BOURDON
SET POINT KNOB
INNER MOVEMENT
OUTER MOVEMENT
FLAPPER
NOZZLE
RESTRICTOR
OVERTRAVEL
SPRING
INLET PORT
ZONE “A”
EXHAUST PORT
OUTPUT
ZONE “B”
PROPORTIONAL BAND
PROPORTIONAL
FEEDBACK CAPSULE
OUTPUT
OUTPUT
GAUGE
NOZZLE
DIAPHRAGM
SUPPLY
AIR
SET POINTER
(RED)
A
G
F
H
B
C
E
D
P
K
C
P
S
M
N
L
M
RESET CHAMBER
PROPORTIONAL
+ RESET
RESET VALVE
RESET CHAMBER
PROPORTIONAL
+ RATE
RATE VALVE
RESET CHAMBER
PROPORTIONAL
+ RESET + RATE
RESET VALVE
RATE VALVE
RATE
RESET
RESET RATE
RESET CHAMBER
PROPORTIONAL
+ RESET
RESET VALVE
RESET CHAMBER
PROPORTIONAL
+ RATE
RATE VALVE
RESET CHAMBER
PROPORTIONAL
+ RESET + RATE
RESET VALVE
RATE VALVE
RATE
RESET
RESET RATE
Figure 10
Controller Diagram