Problem
Random noise is noise that has no discernible pitch. Random noise can
be caused by electrical problems. It sometimes sounds like static on a
radio or sometimes is described as "bacon frying." Random noise
is also caused by mechnical problems such as bearing problems, gearboxes
(especially when the motor runs at high speeds), and brushes in brush-type
servo motors.
Random noise can be caused by:
- Low-resolution feedback.
- Wiring noise (electromagnetic interference or EMI).
- Excessively long cables.
- Ground loops.
- Excessive servo gains, especially the proportional velocity gain.
- Gear noise, especially when the motor is rotating at high speed or
when "antibacklash" gears are used.
- Bearings.
- Belts.
- Six-step commutation, which produces rich harmonics.
- In brush-type servo motors, brushes sliding on commutator surface.
- In brush-type servo motors, EMI generated from brush arcing.
Verification
Random
noise is directly observable and ususally does not require verification.
A noise that is loud enough to be objectionable and that has no discernable
pitch, is usually random noise.
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