Slip Ring Design: What are the Key Parameters?

 As a connecting component of various electromechanical devices, slip rings can transmit power and electrical signals from a fixed structure to a rotating structure. When we design slip rings, whether in standard or custom specifications, we need to select the suitable parameters to ensure their normal operation. So, do you know what important parameters slip rings have?

Electrical Parameters

1. Number Of Circuits

The number of circuits of a slip ring refers to the number of independent signal channels that can be transmitted simultaneously. For example, a 10-circuit slip ring can transmit 10 different signals simultaneously. The more circuits there are, the more complex the structure of the slip ring becomes and the more difficult it is to manufacture. At the same time, it may also affect the stability of the slip ring, because more signal channels mean more potential failure points.

 

2. Rated Current/Voltage

lRated Current: It refers to the maximum current allowed by the motor when the slip ring operates in a normal working mode, expressed in units of A. This is often determined by the contact material area and conductivity of the slip ring components. If the rated working current is exceeded, the temperature at the contact position of the slip ring rises sharply, and phenomena such as contact separation and poor contact may occur.

lRated Voltage: It refers to the maximum applied voltage when the slip ring works safely, expressed in units of V. The insulating material and installation space of each slip ring affect its fixed working voltage. When the voltage of the slip ring exceeds the rated value, it may overheat, burn out or even cause a safety accident.

 

3. Signal Type

Slip rings can transmit various types of signals, including analog signals (voltage signals, current signals), digital signals (bus signals, serial port signals), radio frequency signals (various wireless communication signals), etc. They have different requirements for slip rings. For example, analog signals are more sensitive to the contact resistance and signal interference of slip rings; digital signals have higher requirements for the transmission rate and bit error rate of slip rings...

 

4. Signal Rate

The signal rate refers to the maximum data transmission rate of the signal that a slip ring can transmit. It has two units.

lSymbol Rate: which refers to the number of symbols transmitted per unit time.

lData Transmission Rate: the amount of information transmitted per second, in units of bits per second (b/s or bps).

Some fieldbus signals, such as Profibus, DeviceNet, and CAN, have relatively low rates. High-rate signals are generally computer protocol signals, such as USB, HDMI, and Ethernet signals. These signal rates can reach more than 100 Mbps. The higher the signal resolution, the greater the signal rate.

 

Mechanical Parameters

1. Product Size:

lInner Diameter: (in slip rings with through holes) refers to the diameter of the central hole of the slip ring.

lOuter Diameter: the maximum outer diameter of the slip ring.

lHeight: the size of the slip ring in the vertical direction.

The inner diameter of the slip ring determines the size of the shaft it can pass through. If the inner diameter is too small, it may not be possible to install it on the required equipment shaft. On the contrary, it will lead to insecure installation. A larger outer diameter and height can provide more space to arrange electrical contacts and wires. This helps reduce the contact resistance and signal interference of the slip ring during operation. But if they are too large, they will increase the path length of signal transmission and lead to signal attenuation.

 

2. Protection Level:

The protection level refers to the ability of the slip ring to protect against dust, water and other external pollutants. It is usually represented by an IP code and ranges from IP54 to IP68. Specific as follows:

lIP54: Slight dustproof and waterproof splashing.

lIP65: Highly waterproof, and water droplets will not enter the inside of the slip ring.

lIP68: Completely waterproof and can work in low-depth underwater areas, such as underwater radars.

They vary according to the application environment of your equipment. Note that a mismatched protection level can easily cause slip ring failure.

 

3. Operating Speed

The speed refers to the maximum rotational speed that the slip ring can withstand under normal working conditions. It is designed according to the requirements of the equipment and is expressed in revolutions per minute (RPM). When the equipment speed reaches tens of thousands of revolutions per minute, then the speed of the slip ring also needs to reach tens of thousands of revolutions per minute. In addition, the speed is affected by many aspects, including contact friction, the internal structure of the slip ring, and the dimensional accuracy of components.

 

4. Operating Temperature/Humidity

They refer to the temperature range and relative humidity range that the slip ring can withstand under normal working conditions. For example, slip rings can usually operate at temperatures from -40°C to +85°C, and the working humidity ranges from 10% RH to 95% RH. When the surrounding temperature is too high, the insulating material in the slip ring will become brittle and age or even break down. This may lead to equipment shutdown. And excessive humidity will also cause rust and corrosion on its contact parts, and the signal transmission quality will be reduced.

 

5. Anti-Seismic/Impact Resistance Requirements

This is the ability of the slip ring to maintain normal operation when subjected to vibration or impact. It is usually represented by the magnitude of acceleration or impact force, ranging from several tens of G to several hundred G. This is related to the slip ring material, installation method and sealing structure. If the internal structure of the slip ring is damaged, the electrical contact part is loosened or disconnected. We need to check whether the installation method of the slip ring is correct and whether the size matches the bearing parameters.

 

6. Installation Method:

The installation methods of slip rings are divided into flange installation and through-hole installation. The former fixes the slip ring on the equipment through a flange, which is relatively firm but requires a larger installation space. The latter installs the slip ring through the central hole of the equipment.

Some large industrial equipment and aerospace equipment often use flange installation. Small electronic equipment, medical equipment and other applications with limited space prefer through-hole installation.

 

Conclusion

Understanding the meaning of slip ring parameters can help you better desing and use slip rings. Now let's summarize, we need to consider electrical parameters such as the number of circuits, rated current/voltage, signal type and signal rate of the slip ring. At the same time, the size, protection level, operating speed, temperature and humidity, seismic resistance and installation method of the slip ring are also important.

By the way, if you have any doubts about slip ring process, please refer our article”How to Make a Slip Ring?”. It may be helpful to you.