Example: Pto Direction Of Action - Samson 3738-20 Mounting And Operating Instructions

9.2.3 Example: PTO direction
of action
The valve is normally open (operating posi-
tion = 100 %). In the event of emergency, the
valve is to close (fail-safe position = 0 %).
The actuator's direction of action is therefore
PTO (power to open), configured in the P5
parameter.
The upper end position (P8) is set at 98 %.
This value is the same as the default setting.
Contact B is activated when the valve moves
beyond this value.
To prevent the valve seizing in the open posi-
tion, a partial stroke test is to be performed
on a weekly basis. During the partial stroke
test, the valve is moved from the operating
position towards the fail-safe position to a
step end of 90 % by briefly de-energizing
the solenoid valve. During the test, the valve
must not move beyond a position of 85 %
and a status message is activated for moni-
toring purposes if the PST target range is not
reached or exceeded.
The following settings are made to the initial-
ized electronic limit switch in the example
while taking the process conditions into con-
sideration:
1. Select configuration mode SET (P2)
The parameters required to configure the
partial stroke test can only be set in the
SET configuration mode (P2 = SET).
EB 8390 EN
2. Define PST target range (P14, P15)
The PST target range is made up of the
'PST step end' (P14) and the 'PST toler-
ance band' (P15). The test has been suc-
cessfully completed when the valve
reached the position of the step end ±
half the step tolerance band, but not
moved beyond it.
P14 ('PST step end')
P15 ('PST tolerance band') = 10 %
g PST target range = 90 % ± 5 %
3. Activate the monitoring of the PST tar-
get range (P12)
The monitoring of the target range as
well as the status readout F6 'Min. value
for PST not reached' and F7 'Max. value
for PST exceeded' are activated by the
P12 parameter = YES.
When the status message F6 or F7 is
generated, check the attachment, supply
air lines and the valve. The setting for the
target range might need to be adapted
in the P14 and P15 parameters. See
"Define PST target range (P14, P15)" in
point 2.
4. Start automatic PST (P16)
P16 = 7 days
The test starts automatically once a week
after switching to RUN operating mode.
The valve leaves the operating position
(100 %) without a switching demand.
Operation
= 90 %
= 85 to 95 %
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