After the valve positioner loses 4-20mA power and then the 4-20mA supply is restored, can the valve immediately return to its original opening degree?
Thread Content
For the Memosyn dual-action valve positioner, after the 4-20mA signal is interrupted and then restored, can the valve return to its original opening position immediately?
Most AO devices have only an output function; it is this type that allows for the immediate restoration of the valve opening degree corresponding to the value output by the DCS/PLC before the connection was interrupted
Sure, as long as the output remains unchanged.
As shown in the figure； Can the actuator still function after the locator signal interruption is resolved?
It should be like this, unless the output signal changes
In this scenario shown in the diagram, there is no solenoid valve; only the air supply is cut off while the power remains connected. If enough time passes, the valve will eventually end up in the fully open position； Only if there is a power loss but no loss of air supply, and enough time is available, then based on the principle of the positioner, the final position could be either fully open or fully closed
After a power outage, as long as the DCS output remains unchanged, the valve opening will stay at its original level.
Power supply? 4~20mA is the signal source
As long as the input signal to the positioner remains unchanged, it can be ensured that the opening degree stays constant; this requires the system to return to its state before the power loss when power is restored.
Generally, it works like this: you set a value, and when the connection is interrupted, it returns to its original opening degree