Spring Control - Engineering Notes

Spring Control:

Two hair springs are attached to the moving system which exerts controlling torque. To employ spring control to an instrument, following requirements are essential.

• The spring should be non-mechanical stress.
• The spring should be free from mechanical stress.
• They should have small resistance and sufficient cross sectional area.
• They should have low resistance temperature coefficient.

Spring Control

Springs are made up of non magnetic materials like silicon bronze, hard rolled silver or copper, platinum silver and german silver. Foe most of the instruments phosphor bronze spiral springs are provided. Flat spiral springs are used in almost all indicating instruments.

The inner end of the spring is attached to the spindle  while the outer end is attached to a lever or arm which is actuated by a set of screw mounted at the front of than instrument. So zero sitting can be easily done. The controlling torque provided by the instrument is directly proportional to the angular deflection of the pointer

Advantages of Spring Control:

1. Scale is uniform.
2. The readings are taken very accurately.
3. The system need not be in vertical position. It can be used in any position. 
4. This control is mostly used when compared to gravity control.

Disadvantages of Spring Control:

1. The controlling torque is fixed.
2. The performance is temperature dependent.
3. It is simple, rigid but costlier.