Design and principle of operation
6
EB 7065 EN
3
Design and principle of op-
eration
The controller mainly consists of the controller
housing containing a nozzle and flapper sys
-
tem, pressure gauges for supply air and out-
put pressure as well as the temperature sensor
with an outer tube (11) and Invar rod (12).
The different expansion properties of the In-
var rod and tube materials produce a de-
flection each time the temperature at the sen
-
sor changes. This deflection causes the differ
-
ential plate (3) mounted on the plate spring
(9) to tilt on the ball (5), and causes the dis-
tance between the nozzle (2) and flapper (4)
to change. The supply air p
Z
(1.4 ± 0.1 bar)
flows through the restriction (1) to the nozzle
(2). These two components act as a pressure
divider controlled by the flapper. As a result,
the output pressure p
A
(controlled variable 0.2
to 1 bar) is regulated proportional to the sys
-
tem deviation and in relation to the fixed op
-
erating point of 0.6 bar.
The set point is adjusted at the screw (8) con-
nected to the set point pointer (7). The pro-
portional band is adjusted at the adjustment
screw (6). The position of the red dot on the
screw (6) indicates the operating direction ad-
justed.
Position in scale range
^^
: The output pres-
sure p
A
increases as the controlled variable
increases.
Position in scale range
^
^
: The output pres-
sure p
A
decreases as the controlled variable
increases.
Fig. 1:
Functional diagram of Type 3301
1 Restriction
2 Nozzle
3 Differential plate
4 Flapper
5 Ball
6 Adjustment screw for Xp
(proportional band)
7 Set point pointer
8 Screw for set point adjustment
9 Plate spring
10 Base plate
11 Outer tube
12 Invar rod
p
Z
Supply air (1.4 ± 0.1 bar
)
p
A
Output pressure (0.2 to 1 bar)
p
Z
p
A