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MT Series SSC Electronic Valve Actuator, 24 Vac/dc Proportional Control
Operation
Siemens Industry, Inc.
The stroke of the actuator shaft is proportional to the control signal on terminal Y.
A 0 Vdc control signal retracts the shaft. In the event of a power failure with no control
voltage, the SSC61U fails-in-place and holds its last position.
In the event of a power failure, the SSC61.5U returns to the stem up position. The
SSC61.5U includes an electronic return mechanism that functions as follows (Figure 1):
·
At power-up (t0), a capacitor
must charge to its maximum
capacity (Max, tc). This will take
a maximum of 180 seconds,
during which time no actuator
movement occurs.
·
Once the capacitor is fully
charged (tc), normal actuator
operation occurs.
·
If a subsequent power failure
occurs (tn) longer than 5
seconds, the capacitor
discharges (td) and the actuator
returns to its normal spring
return position.
Document Number 155-313P25
Figure 1. SSC61.5U Electronic Spring Return
Mechanism.
CAUTION:
Before applying power, make certain a valve
is connected to the actuator.
If applying power to the actuator when a
valve is not connected, the actuator will
respond to a control signal and the shaft will
extend until it reaches its maximum end stop.
Thereafter, it will not respond to any signal.
If this occurs:
1. Disconnect power.
2. Turn the manual position indicator (see
Figure 5 and Figure 6) on the top of the
actuator to the 0 position and verify that
the actuator shaft retracts completely.
3. Connect a valve to the actuator, and
reapply power. The actuator will return to
normal operation.
Technical Instructions
January 12, 2018
Page 3
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