Curioustab Logo Curioustab
Home » Electronics and Communication Engineering » Measurements and Instrumentation

A speed transducer that uses a drag-cup rotor (e.g., drag-cup tachogenerator) has which principal advantage compared with conventional designs?

Difficulty: Easy

Correct Answer: Low energy requirement due to very low rotor inertia

Explanation:


Introduction / Context:
Drag-cup tachogenerators and similar speed sensors use a thin, lightweight conducting cup instead of a solid rotor. This design significantly reduces mass and inertia, improving dynamic response and lowering the torque required to drive the sensor—ideal for delicate shafts and low-speed applications.


Given Data / Assumptions:

  • Drag-cup rotor has very small moment of inertia compared with slotted or solid rotors.
  • Sensor output is proportional to speed via electromagnetic induction.
  • Application values low loading of the prime mover and fast response over extreme accuracy claims.


Concept / Approach:
The key performance driver is mechanical loading. The transducer should minimally disturb the system it measures. A drag-cup produces the needed EMF with negligible mechanical torque demand, hence low energy requirement. While accuracy can be good, it is not inherently 'very high' compared with all other sensor types, and cost depends on build quality, so 'all of the above' is not appropriate.


Step-by-Step Solution:

Identify property most directly tied to the drag-cup construction: low inertia.Relate low inertia to low energy/torque requirement and minimal shaft loading.Conclude option highlighting low energy requirement is correct.


Verification / Alternative check:

Compare dynamic response and starting torque specs of drag-cup vs. conventional tachos; drag-cups have markedly lower drive torque.


Why Other Options Are Wrong:

'Very high accuracy' is not universally true; many factors affect accuracy (linearity, temperature, electronics).'Cheapest construction' is not guaranteed.'All of the above' bundles incorrect statements.


Common Pitfalls:

Assuming every advantage applies; always tie the benefit to the physical construction.


Final Answer:

Low energy requirement due to very low rotor inertia
← Previous Question Next Question→

More Questions from Measurements and Instrumentation

Discussion & Comments

No comments yet. Be the first to comment!
Join Discussion