Electrical Engineering ⇒ Topic : Gravity Control
Gravity Control. In this method, a small adjustable weight W is attached to the moving system [See **Fig. a (i)] which provides the necessary controlling torque. In the zero position of the pointer, the control weight hangs vertically downward and therefore provides no controlling torque. However, under the action of deflecting torque, the pointer moves from zero position (from left to right) and control weight moves in the opposite direction. Due to gravity, the control weight would tend to come to original position (i.e. vertical) and thus provides an opposing or controlling torque. The pointer comes to rest at a position where controlling torque is equal to the deflecting torque.
In the deflected position shown in Fig. a (ii), weight W can be resolved into two rectangular components viz W cos θ and W sin θ. Only the component W sin θ provides the controlling torque TC.
Since I is proportional to the sine of angle of deflection, gravity-controlled instruments have non-uniform scales ; being crowded at the beginning as shown in Fig. a (i).
The schematic diagram for gravity control is shown in Figure (a). The following points should
be noted for gravity control:
The gravity-controlled instruments are operated vertically.
Gravity-controlled instruments are cheaper.
These instruments are independent of temperature and ageing.
Instrument reading is proportional to the sine of the angle, i.e., Tc ∝ g sin θ.
figure (a) Gravity control
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