Gravity Control

In gravity controlled instruments, a small weight is attached to the moving system in such a way that it produces a controlling torque, when the moving system is deflected position. The controlling torque can be varied quite easily by adjusting the position of controlling weight upon the arm. Another weight is attached for zero adjustment and balancing purposes. This weight is referred to balancing weight. Gravity control is cheap, unaffected by change in temperature and is free from deterioration with time but it gives a cramped scale and the instrument has to be kept in vertical position.

What You Need To Know About Gravity Control

• In gravity control, adjustable small weight is used which produces the controlling torque.
• The system must be used in vertical position only in gravity control.
• The readings cannot be taken accurately in the gravity.
• In gravity control, the performance is not temperature dependent.
• Controlling torque can be varied in gravity control.
• The scale is non-uniform in gravity control.
•  Proper leveling is required as gravity control.
• Simple, cheap but delicate.
• Rarely used for indicating and in portable instruments.

Spring Control

Spring control is the most popular method of providing controlling torque in electrical instruments. It usually involves one or more springs. A spiral hairspring made of a non-magnetic material such as phosphor bronze is attached to the moving system. When the pointer deflects the spring twists in the opposite direction producing a restoring torque proportional to the angle of deflection of the moving system. In an instrument where the deflecting torque is uniform, spring control provides a linear or evenly spaced scale over a whole range.

What You Need To Know About Spring Control

• In spring control, two hair springs are used which exert controlling torque.
• The system need not be necessarily in vertical position in spring control.
• The readings can be taken very accurately in the spring.
• In spring control, the performance is temperature dependent.
• Controlling torque is fixed in spring control.
• The scale is uniform in spring control because of direct proportionality between deflection angle and current flow in spring control system.
• The leveling is not required as spring control.
• Simple rigid but costlier when compared to gravity control.
• Very popularly used in most of the instruments.

Also Read: Difference Between Mass And Weight

Difference Between Gravity And Spring Control