# Test and Measurement World

## Test and Measurement World Terminology Section

One Stop For Your Test and Measurement Need

## Spring Control Vs Gravity Control | Difference between Spring Control and Gravity Control

This page compares Spring Control Vs Gravity Control and mentions difference between Spring Control and Gravity Control.

### Spring Control A hair-spring made of phosphor-bronze is attached to the moving system. It is used in indicating instruments for control purpose. The figure-1 depicts schematic arrangement of spring control.

The number of turns on the spring should be fairly large in order to provide control torque proportional to angle of deflection of the moving system. Hence deflection per unit length is small. The stress in the spring must be limited to such a value that there is no permanent set.

Controlling torques is expressed by following equation.
Tc = ( E*b*t3/12*L )* θ
Where,
L = Total length of strip with rectangular cross section in m
t = radial thickness in m
b =depth in m
E = Young's modulus in N/m2
θ = deflection of moving system in radians

### Gravity Control Small weight is connected with moving system in gravity control instrument. The attachment is made such that system produces controlling or restoring torque when system is deflected. This is shown in the figure-2.

Controlling torques is expressed by following equation.
Tc = w*l*sin(θ)
Where,
w = control weight
l = distance from axis of rotation of moving system
θ = angle of deflection