In the case of a control, the signal is transferred only in one direction. There is always one open action flow or one open impact chain (Figure S 87 a).
A control chain as a whole can always be connected to further systems in any functional relationship within a parent system (DIN 19 226) (b).
A control can be considered as a chain (or series circuit) of several subsystems: For example, one subsystem is the plant to be influenced, in fluid technology this is often a cylinder with a connected load, the second subsystem is the immediately upstream control device, for example a proportional directional valve with its electronic activation amplifier and the third subsystem is a device which provides the electrical setpoint signals for the proportional directional valve.
Figure S 87: Control chain (a) and control chain with controlled element (b)