Current Control
A closed loop drive method that forces the target current onto the coil instead of a fixed voltage. Because the drive continuously measures the actual current and corrects the PWM duty cycle, the same command produces the same flow rate even when the coil heats up and its resistance increases; it largely eliminates temperature induced drift.
The resistance of a coil increases with copper temperature; a winding going from 20 °C to 100 °C typically rises in resistance by about one third. If the voltage is held constant the current drops by the same ratio, the spool opens less and the operator feels a slower motion at the same lever angle. In current controlled drive the loop works like this:
- The command is converted to a target current value (for example 700 mA).
- A sense resistor or current sensor reads the actual current.
- The PWM duty cycle is automatically increased or decreased until the difference is zero.
The result is a flow characteristic that does not change whether the supply voltage drops to 11 V or rises to 15 V. The same logic applies in AXI's servo based retrofit kits: because lever position is supervised by feedback, when the battery weakens the target position is maintained, only the speed of reaching it drops somewhat.
Where this term is used: What Is a Hydraulic Lever Retrofit Kit? Definition, Components, Operating Principle