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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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When the damping force is more than the optimum, the instrument will become
Dead
Oscillating
Slow and lethargic
Fast and sensitive
Slow and lethargic
Quick Summary: When the damping force exceeds the optimum (critical) damping level, the instrument becomes overdamped. This causes the pointer to approach its steady-state position very slowly, resulting in a lethargic and sluggish response.
When the damping force exceeds the optimum (critical) damping level, the instrument becomes overdamped. This causes the pointer to approach its steady-state position very slowly, resulting in a lethargic and sluggish response.
Dc=2KJ — critical damping coefficient
ζ=2KJD — damping ratio
An instrument's response is governed by the second-order differential equation Jdt2d2θ+Ddtdθ+Kθ=Td. When D>Dc (where Dc=2KJ is the critical damping coefficient), the system is overdamped. The roots of the characteristic equation are real and negative, preventing oscillation but significantly increasing the time required for the pointer to settle.
Critical damping (ζ=1) is usually desired for the fastest response without oscillation.
Overdamping (ζ>1) leads to a sluggish response.
Underdamping (ζ<1) leads to overshoot and oscillations.
Damping torque is generated by eddy currents, fluid friction, or air friction.
Prevents oscillations around the equilibrium position.
Protects the pointer mechanism from erratic swings.
Excessive damping increases measurement time significantly.
May lead to reading errors due to slow response to signal changes.
Moving coil instruments
Analog voltmeters and ammeters
The 'optimum' state is defined as being slightly underdamped or critically damped for a balance of speed and overshoot.
Option B (Oscillating) corresponds to an underdamped state.
Option A (Dead) is a misnomer, as a dead instrument typically implies no movement at all (e.g., open circuit).
C is correct — When damping is greater than critical, the instrument becomes overdamped, resulting in a slow and lethargic movement of the pointer.
Always remember: Critically damped systems reach steady state the fastest without any overshoot, making them ideal for high-precision measurement.