Closed Loop Valve Control
A control structure in which the actual position of the valve spool or actuator is measured and continuously compared against the command. Because drive current is corrected until the error goes to zero, hysteresis, temperature drift, and load variation are largely suppressed; the system looks at the result, not the command.
The loop repeats hundreds of times per second: measure, compare, correct. What this structure delivers is concrete:
- When the solenoid heats up and its resistance rises, current is automatically increased and flow rate stays constant.
- When the load gets heavier, the spool opens somewhat further and speed is maintained.
- Even as the valve wears over time, the target position continues to be met.
The cost is sensor expense, wiring, and tuning effort. If gain is set too high, the system oscillates around the target; if set too low, it becomes slow and delayed. Also, since a sensor fault can now by itself lead to a dangerous condition, the feedback line must be monitored for breaks.
AXI's HCT400 and HCT402 kits apply this logic to the lever rather than the valve: the servo motor holds the lever on target with typically ±1° accuracy by feeding back its position. Even if the vehicle's own valve is open loop, the lever side runs closed loop.
Where this term is used: The Importance of Hydraulic Control: Why Should It Be Commanded by an Electronic Signal?