Samson Series 420, Руководство пользователя

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18 EB 7500 EN
Design and principle of operation
5.6 Type 3423 Controller
Modules
See
u
T 7521. The controller modules are
plug-in units which are inserted onto the self-
seal push-on fittings of a manual control sta-
tion, manual control unit, or control room or
field housing. The controller modules are
held in place by a screw.
The controller modules consist of a compara-
tor fitted with four metal bellows arranged in
a square and a base plate with self-seal
push-on fittings.
The base plate accommodates the compo-
nents required for the chosen function, such
as relays and restrictors. The components
can be exchanged or upgraded, allowing
the function to be changed at a later point in
time (see section 9.1).
Type 3423-2 PI Controller (Fig. 10, top)
The controlled variable x and the reference
variable w (set point) are transferred as
pneumatic signals between 0.2 and 1 bar
via turnboard
A to the metal bellows w and
x. When x is greater than w, the controlled
variable bellows tilts the pivoted swashplate
toward the set point bellows, causing the
pressure downstream of the nozzle connect-
ed to the swashplate over a pin to rise. As a
result, the output pressure yA of the booster
increases. The pressure yA is fed back imme-
diately via turnboard
B to the bellows R2 on-
to the swashplate.
The position of the swashplate and the out-
put pressure yA keep changing until the dis-
tance between nozzle and flapper is the
same as initially and the output pressure yA
assumes a value corresponding to the con-
trolled variable x and the adjusted propor-
tional-action coefficient Kp adjustable over a
screw.
Outside of the controller module, the
yA is
connected to R , allowing the pressure yA to
be fed back to bellows R1 also over the port
R and the adjustable Tn restrictor. As a re-
sult, the effects of the pressures in bellows R1
and R2 balance themselves out and the error
deviation is eliminated.
A switchover to manual mode at the control-
ler station causes a switching pressure to be
applied to port
S . The Tn start-up relay is ac-
tivated and bypasses the Tn restrictor.
The
turnboard A determines the direction of
action of the controller. The direction of ac-
tion can be changed by turning the turn-
board (see section 3.1.1).
The
turnboard B determines the air delivery
to the feedback bellows.
In the delivered state, the turnboard B is set
to yA, i.e. the output pressure yA is directly
fed back to bellows R2. Whereas, it is fed
via connection
R to bellows R1. With this cir-
cuit arrangement, the controller provides
normal air delivery and output pressure
damping.
In the switching position to
R , the output
pressure yA is fed back via port R to the bel-
lows R1 and R2. As a result, the controller
has a higher air delivery. Practical applica-
tion for long distances to the control valve,
large connecting volumes and for fast con-
trolled systems.
See section 3.1.2 on how to set or change
the air delivery by turning the turnboard
B .