Proportional spools slide in cast body – No sleeve, in main stage (unlike a servo valve) – Robust construction similar to on/off directional valves –…

LVDT position feedback improves performance – Increased flow capacity – Higher Power Limit – Better Response Sensitivity – Better Hysteresis < 0.3%  

Adding LVDT position feedback greatly improves resolution 0.2% Hysteresis  

Improve accuracy and performance with position feedback on solenoid LVDT – Linear Variable Displacement Transformer Position transducer – short stroke High resolution Non-contacting Robust

Solenoid force vs. spring force positions spool Select one solenoid to control direction and flow 40% input Sol-a => 15% flow P-to-B 80% input Sol-b…

Solenoid force opposed by spring force = rate x displacement Spool position is constant, when forces are balanced Input (coil current) is directly proportional to…

Solenoid force opposed by pressure P x A (area seat 3) Input to amplifier changes solenoid current (output Force) 20% input => 20% pressure 80%…

Solenoid current is proportional to armature force, unlike on/off solenoid This proportional force is linear within a working stroke (approx 1.5 mm) Given a constant…