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▶ The definitions of relays
The relay is an automatic control element whose output variable undergoes a change by leaps and bounds when its input variable (electric, magnetic, sound, light, heat) reaches a set point.
▶ Relaying attribute of the relays
When the input signal x grows continually from zero to the action value xx upon the pulling-on of the armature iron, the output signal of the relay will jump from y=0 to y=ym, i.e. the normally open contacts from off to on. As soon as the contacts are connected, the input variable x continues to rise while the output variable undergoes no further change. When the input variable drops from a value larger than xx to xf, the relay begins its release, the normally open contact breaks off (see Diagram 1). We call this attribute of the relay the electric relaying attribute or the input-output attribute of the relay.
The ratio of the release value xf to the action value xx is called the feedback coefficient, i.e. Kf = Xf / Xx T The ratio of the output control power Pc on the contact to the minimum power Po absorbed by the coil is called the control coefficient of the relay, i.e. Kc= Pc/