In a broader sense, proportional control technology is a collective term for all the various uses of continuously adjustable valves and also therefore of servo valves. On a day-to-day basis, however, the term is restricted to the increasingly varied use of proportional valves, i.e. it actually covers proportional valve technology.
Key characteristics of proportional technology are the continuous, proportional transfer function associated with the valves and the amenability to control via electrical signals of the functions for flow rate based on direction, size and pressure.
In hydraulics:
Here, regardless of whether a control or feedback control is ultimately involved, the full range of electronic signal processing options is available for hydraulic drives.
Moving from a switching-based to a continuous form of actuation makes it possible to adjust the operating variables for a process - particularly forces, velocities and positions - in line with optimal operating conditions and also improve the of the system. In addition, the constant refinement of proportional valves has led to an increasing use of proportional technology in feedback control applications too (Figure P 21).
- same mounting dimensions as switching valves.
The main advantages of proportional technology are as follows:
- direction and flow control in a valve,
- low pressure drop at control edges,
- mastery of acceleration and deceleration processes via electronic specifications (ramps),
- same mounting dimensions as switching valves.
The use of proportional technology also offers considerable advantages in "normal" hydraulics by making it possible to simplify circuits greatly, with fewer pressure and flow valves needed thanks to the control valves used (Figure P 22).
Figure P 21: Schematic representation of a circuit with a proportional valve
Figure P 22: Control with normal valves (a) and with proportional valves (b)