Describe spring control method of producing controlling torque in measuring instrument. Write any two properties required for spring material.
A)Spring control method: As shown in the figure, the inner ends of the both springs are attahced to the spindle, while outer end of upper spring is attached to the lever and outer end of the lower spring is fixed. With the deflection of the pointer, the springs are twisted in opposite direction to the motion of pointer and produce controlling torque.
Properties of spring material: 1.Non Magnetic material 2.Low specific resistance 3.Low temperature coefficient of resistance