Samson 3730 Series, Mounting And Operating Instructions

Page: 34 / 72

5.1.1 Signal pressure gauges
To monitor the supply air (Supply) and sig-
nal pressure (Output), we recommend that
pressure gauges be attached (see accesso-
ries in Tables 1 to 5).
5.1.2 Supply pressure
The required supply air pressure depends on
the bench range and the actuator's operat-
ing direction (fail-safe action). The bench
range is registered on the nameplate either
as spring range or signal pressure range.
The direction of action is marked
FA
or
FE
,
or by a symbol.
Actuator stem extends FA
(Air to open
ATO)
Fail-safe position "Valve Closed"
(for globe and angle valves):
Required supply pressure = Upper bench
range value + 0.2 bar, minimum 1.4 bar.
Actuator stem retracts FE (Air to close ATC)
Fail-safe position "Valve Open"
(for globe and angle valves):
For tight-closing valves, the maximum signal
pressure pst
max
is roughly estimated as fol-
lows:
pst
max
= F +
d p
A
2
4
⋅ ⋅
⋅
π ∆
[bar]
d = Seat diameter [cm]
∆
p = Differential pressure across the valve
[bar]
A = Actuator diaphragm area [cm²]
F = Upper bench range of the actuator
[bar]
If there are no specifications, calculate as
follows:
Required supply pressure =
Upper bench range value + 1 bar
Note: The signal pressure at the output (Out-
put 38) of the positioner can be limited to
approx. 2.4 bar by setting the parameter
P9
= ON .
34
EB 8384-1 EN
Connections