Slip Ring Material Application Recommendations
When choosing the appropriate slip ring for an application several factors are involved. Usually the first things to consider are the voltage and current levels. For power circuits (high voltage and current) this is very straightforward. The circuit is chosen to meet or exceed the voltage and current levels present. When dealing with low-level signal circuits there is another factor to consider. The primary obstacle at low levels is noise. Electrical noise is defined as an undesirable variation in the voltage or other characteristic of an electrical signal. This undesirable variation can originate from outside the circuit (induced) or from within the circuit (generated).
Induced noise is caused by power circuits that carry large transients being in close proximity to the signal circuits, (e.g. variable frequency speed controls, large servo drives, welders). When both signal and noisy power circuits pass through the same ring, assembly shielding must be used to prevent induced noise from reaching the signal circuits.
The primary cause of generated noise in the slip ring assembly is the variation of resistance of the brush to ring interface. Due to the conductivity of different materials this interface will have differing resistances. The less expensive standard circuits have a slightly higher initial resistance than the silver circuits. As a ring rotates this resistance will vary slightly, with the standard circuits having more variation than the extended pressure (see description below) or silver circuits. The combination of current flow through this varying resistance creates a voltage variation. The level of this variation in respect to the actual signal level creates the signal to noise ratio. Specified as S/N. It must be kept in mind that environmental factors must be taken into consideration for selection not just signal performance. For example in a hostile environment such as a high moisture or a corrosive atmosphere, or an application that sees long periods of non-use, a higher grade material may be needed to reduce surface degradation.
Basic Material Descriptions
The standard slip ring circuit consists of a pair of sintered metal copper/graphite brushes making contact with a brass ring. The least expensive solution and sufficient for most applications including low level audio, video and network* signals when used in protected areas and frequent use.
Extended Pressure Circuits
The extended pressure slip ring circuit is a standard circuit with the brush profile/radius changed to increase the surface pressure in the contact area. This provides better cleaning action and tighter contact for a quieter interface than the standard circuits. The tradeoff is shorter life in high cycle applications. Used in areas of moderate possibility of corrosion for higher cleaning action and low voltage signal circuits. Also circuits with long periods of non-use. Use for low-level signal circuits on equipment used outdoors or in areas of moderately corrosive environments.
Silver Brush Circuits
The silver brush circuits are a pair of silver graphite brushes on a standard brass ring. This gives a signal that is very comparable to the full silver circuits at a lower cost. The tradeoff is that the brass ring could still corrode in hostile environments or with long periods of non-use. Use for sensitive low-level circuits, critical network*, audio or video circuits with intermittent use and long periods of non-use.
Full Silver Circuits
The full silver circuits are a pair of silver graphite brushes on a coin silver or silver plated ring. This is the ultimate circuit with the highest cost due to the precious metal ring. This circuit will provide a clean signal even in applications of long periods of non-use and moderately corrosive environments. Used for the most critical circuits where signal integrity is of utmost importance. Also used in corrosive environments where brass or copper would loose signal integrity due to surface corrosion. Use for critical network*, audio, video or low level analog circuits in wet or corrosive environments.
Basic Application Summary
All power and signal circuits above 24 volts can be used with standard circuits.
Low voltage signals (5 to 24) in clean dry atmosphere can be used with standard circuits. For wet or corrosive atmosphere consider extended pressure or silver brushes.
For millivolt (thermocouple) to 5 volt signals or critical signals or in corrosive atmospheres full silver circuits should be used.
* The term network is intended to describe digital data communication including but not limited to those listed below.
- CANBus / CANopen Or J1939
United Equipment Accessories can only make recommendations as to the use of their slip ring products and makes no warranty as to the suitability of their products for any specific purpose. Final acceptance and approval of application is completely the responsibility of the purchaser.