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The effect of rotation on the performance of the slip ring will be discussed here in relation to high data rate transfer. The very basic idea behind the transmission of power and other kinds of the signal is based on the contact mechanism. Things are no different in the case of data transmission. The high-frequency slip ring or the ethernet slip ring too employ the contact mechanism between the ring and the brushes without hindering the rotational motion.
The outcome of rotational motion combined with sliding contact mechanism
As the brushes rub against the ring, the process of transmission
of signals begins. But with the transmission of signals, there is also an introduction of a resistance mechanism as the ring rotates. Similarly, in case of transmission of data signals, the very first issue that pops up is the contact nose. It is just another form or variation of resistance. These contact noise variant of resistance considerably affects the signal transmission.
The contact noise is introduced in the system due to the change in the resistance at the contact points. By contact point, we necessarily refer to the spot where the slip ring and brush come in contact in the normal duration of the entire rotational motion. In order to eliminate the contact noise from the system, the slip ring manufacturer often prefer the incorporation of a minimum two brush contacts which would further help in reducing the variation in resistance.
The slip ring contact materials generally include the use of precious metal, which assists in bringing down the level of high resistance oxidation film formation. Also, the use of a minimal amount of contact lubricant is observed as it also helps in arresting the growth of high resistance organic films. The numbers pertaining to several important factors give us a clear idea about the effect of this contact noise on the data transmission along with changes in rotational motion figures i.e RPM.
When the slip ring is said to rotate anywhere between the range of 10 RPM to 140 RPM, the contact resistance variation normally falls between 10 and 40 milliohms per revolution. Considering the fact that the current level flowing through the system during the digital or data signal transmission tinkers around 20 milliamps, the 10-40 milliohm figure indicates 0.2 to 0.8 microvolts of noise. This can be further represented as -75 dB of noise when we take into account a 5-volt circuit.
The readings of -75 dB of noise might not seem to be concerning issues as it deviates much from the standard set value of -40 dB. But things get a bit trickier when the contact noise gets near to one volt during the starting phase. As this happens, the magnitude of the crosstalk effect rises with the rise in the general noise level.
