Proportional Amplifier
An electronic card that converts the low-power voltage signal from a joystick or controller into the regulated current that drives a proportional valve solenoid. It typically carries minimum/maximum current, ramp, and dither settings; its input is 0–10 V or 4–20 mA and its output is solenoid current up to amperes.
The amplifier does two jobs: power amplification and characteristic shaping. On the power side a PWM output stage drives the solenoid and reads the actual current back across a sense resistor to compare it with the command. On the shaping side the raw joystick signal does not go directly to the valve; it first passes through deadband compensation, gain limiting, and time ramps.
- The Imin / Imax settings write the currents at which the valve starts delivering flow and reaches full opening into the card's memory.
- The ramp setting spreads command changes over time, reducing jolt and load swing.
- The dither setting superimposes a small oscillation on the current to prevent the spool from sticking.
The card can be analog (potentiometer-adjusted) or digital (configured by computer). On digital cards, having the settings stored lets you bring a second unit of the same machine to identical behavior within minutes. When working with electronic retrofit kits, knowing whether this card is present and how it is set explains why the vehicle sometimes responds harshly and sometimes softly.
Where this term is used: The Importance of Hydraulic Control: Why Should It Be Commanded by an Electronic Signal?