Masoneilan SVI3 Installation and Maintenance Manual
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© 2021 Baker Hughes Company. All rights reserved.
3.7 Power Up
3.7.1 Air to Open and Air to Close Actuators
3.7.1.1 ATO / ATC
The positioner must be configured as Air-to
-
Open
,
ATO, or as Air-to-Close, ATC. This
parameter is toggled by the * button.
To determine if an actuator is considered ATO or ATC, perform the following test:
1. Apply the actuators rated pressure to the positioner supply.
2. Disconnect the electrical (4 to 20 mA) input signal from the positioner or set it to less
than 3
.
6 mA.
3. Observe the position of the control valve. If it is:
• Closed the actuator is ATO.
• Open it is ATC.
3.7.1.2 Actuator Action
It is important to correctly assign the sign + or - of each control variable throughout a
control system. Even the control valve subsystem can be complex. Figure 27 and
Figure 28 show the action of air to open, ATO, and air to close, ATC, valves when used
with SVI3. The figures show a direct acting positioner with linear and percentage
characteristics. Some hysteresis is shown for the actuator pressure signal that is caused
by friction in typical actuators. The scales are chosen to emphasize the relationships
between input current and actuator pressure, so that the failsafe valve position is shown
at the lower left of each graph. Note that for an ATC valve, 4 mA represents 100% valve
travel not the expected 0%. The controller and other human machine interfaces must
correctly show that the valve is open 100% at 4 mA and closed 0% at 20 mA. The graph
shows the valve movement and actuator pressure when the Tight Shut-off, T.S., option is
set at about 5%, in this example. The valve movement and actuator pressure are also
shown at the low current lift-off point at about 3.6 mA, below which the positioner is
initializing its settings until power is stabilized.
NOTE : Before powering ON, Please ensure that all the safety requirements described
by ES-817 Product safety Manual is followed. Additionally follow the Section
CAUTION
Do not exceed actuator pressure rating on the control valve
specification sheet. Damage to the valve stem, shaft, or trim can
occur
.
