Salam dear
Partial stroke foe ESDV's should not... never...be done via DCS
There are multiple methods to acheive via ESD
1) OLD school - USE an extra limit switch , make a logic in SIS so that once the command is issued for PST fail close signal will be"pulsed" till it reaches the x% where the limit switch is set.
2) USE smart PST modules , like drallium or made by valve manufacturers, it can be issued via digital output dedicated for PST"not for ESDV open/close"
2) HART compatible PST modules - made by valve manufacturers - to be operated via asset management systems not by SIS directly,