How do you implement online control valve diagnostics for performance monitoring?

Online valve diagnostics identify problems before failure using data from smart positioners and control signals. Diagnostic parameters: friction/stiction (hysteresis, dead band from valve signature), response time (step response test), seat leakage (minimum controllable flow), actuator performance (travel time, air consumption), and positioner tracking. Implementation: configure HART/Fieldbus polling for diagnostic data, establish baseline signatures during commissioning, trend key parameters, set alarm thresholds for degradation. Integrate with asset management software for predictive maintenance scheduling. Combined with control loop analysis identifies whether loop issues are valve-related.