SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES

**Definition:** This place covers:

Systems for controlling or regulating non-electric variables, in particular: position, trajectory, attitude or altitude of a vehicle; position or direction of an object; thickness or size of materials; flow rate; level; quantity ratio; linear or angular speed; force or stress; fluid pressure; torque or mechanical power; vibrations; chemical variables; humidity; temperature; viscosity; and illumination.

"controlling" means influencing a variable in any way, e.g. changing its direction or its value (including changing it to or from zero), maintaining it constant, limiting its range of variation.

"regulation" means maintaining a variable automatically at a desired value or within a desired range of values. The desired value or range may be fixed, or manually varied, or may vary with time according to a predeterminated "programme" or according to variation of another variable. Regulation is a form of control.

Merely acting on a variable for the purpose of influencing the state of a system (e.g. acting on the fuel flow rate in an engine for achieving a certain speed), where the value of the variable itself remains irrelevant, should a priori not be considered as controlling or regulating said variable.

**Glossary:** - Systems: includes self-contained devices such as speed governors, pressure regulators