Increasingly, individual devices are tending to feature internal with a view to preserving or improving certain characteristics.
Typically with integrated controls, the controlled variable tends be an auxiliary variable (a distance in most cases) as opposed to the output variable for the devices concerned. These devices operate in most cases as part of an open loop control system.
Examples: mechanical-hydraulic pressure reduction in flow control valves or for electro-hydraulic linear amplifiers where the measuring spindle is responsible for feeding back the piston travel. Electro-hydraulic control circuits are used in proportional valves where the distance moved by the control element is provided electrically (Figure I 16) or during the controlled adjustment of displacement units where the distance moved by the set piston or the pivoting angle is the controlled variable.
Figure I 16: Internal feedback control for a proportional valve