In traditional brushed DC tachogenerators, the mechanical contact between the brushes and commutator introduces several inherent drawbacks.
First, the friction and wear between these two components increase mechanical torque losses, resulting in higher stiction torque (static friction) at startup or low speed. This directly affects the motor’s low-speed responsiveness and smoothness.
Secondly, the voltage drop across the brush–commutator interface creates a dead zone at low output speeds, where the generated voltage cannot accurately reflect small variations in rotational speed. Furthermore, during commutation, intermittent or poor contact between the brushes and commutator segments can cause arcing, sparking, and electrical discontinuity, generating radio-frequency noise, electromagnetic interference (EMI), high-frequency ripples, and unstable output voltage.
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As stated in literature, “The switching action of the commutator usually causes some arcing which results in electrical noise.” (GD-OTS, Brush-Type DC Motors Handbook)
The mechanical nature of brush–commutator contact also limits reliability in harsh operating environments. In conditions with dust, vibration, high rotational speed, or low humidity, problems such as excessive wear, carbon residue buildup, and contact failure frequently occur (Automate.org, Brushed DC Motor Tutorial).
Given these disadvantages, transitioning from brushed to brushless DC tachogenerator designs has become a key direction for improving performance and reliability. The brushless DC tachogenerator eliminates mechanical contact between the brushes and commutator, thereby removing frictional losses, contact voltage drops, and EMI sources. This structural change dramatically enhances measurement precision, stability, and operating lifespan.
With the advancement of modern electronic control and Hall-sensor technology, it has become feasible to design brushless tachogenerators that maintain the same external characteristics—such as voltage-speed linearity, housing size, and mounting interfaces—as traditional brushed models (Wikipedia, Brushless DC Electric Motor)
Therefore, for DC tachogenerators operating in extreme environments—such as low-speed, high-speed, or dusty and vibrating conditions—the move toward brushless technology is not merely a technical upgrade but a significant improvement in reliability, maintenance cost reduction, and signal stability.
