Electronic control amplifier for proportional valves; often installed on a European circuit board. A specific electronic amplifier card is allocated to a specific type of proportional device:
- valves without a closed loop position control system (force-controlled proportional solenoid),
- valves with a closed loop position control system (stroke-controlled proportional solenoid).
The main functions are power gain (amplification) (voltage/current transformer) between the control signals and the current in the proportional solenoids, compensation for overlap/underlap via a step function generator, generation of ramp functions and setpoint specifications (Figure P 31). Position-controlled valves generally feature the feedback controller and displacement transducer with a cable break monitor (Figure P 32).
Figure P 31: Electronic control system for proportional directional seated valve 1 ramp generator 2 step function generator 3 totaliser 4 flow control valve 5 clock 6 power amplifier 7 power supply unit 8 differential amplifier R1 to R4 = target values R5 = bias current magnet B R6 = bias current magnet A R10 to R14 = ramp time
Figure P 32: Proportional amplifier