Answer to Question #170312 in Electrical Engineering for Derrick

Question

How many operating forces are necessary for successful operation of an indicating instrument? Explain the methods of providing these forces.

Answer 1

1) Deflection Force Or Torque: This isn't he force required to move the pointer from initial position. This could be done using magnetic, thermal, electrostatic, inductive effects.

For example in a PMMC instrument , when the magnetic field of permenent magnet interact with the current carrying coil, the deflection force is produced.

Controlling torque or force: If only deflection force acts, the pointer will not stop it move uncontrolled, and fast. To avoid that a force is required opposite to deflection torque. That is called controlling torque.

Methods of achieving controlling torques are, Spring, gravity control etc.

Damping torque or force: After providing controlling torque the indicating needle will be controlled and moves in controlled speed toward required value. But after reaching their it will keep on oscillating to and fro from actual value. To avoid this a force has to provided. This is called damping torque.

Means to provide it are air friction damping,fluid friction damping and eddy current damping etc.