Data transmission via slip ring in Industry 4.0

Sensors, motors, servo drives, and control systems need to exchange information even when located on continuously rotating parts. Data transmission via slip ring allows connecting these devices from the stationary part of the machine to the rotating one, avoiding cable twisting. In Industry 4.0, a slip ring can be required to handle analog measurements and digital communications, such as CAN bus or industrial Ethernet networks, including Profinet, Profibus, EtherCAT, and EtherNet/IP. Each connection has specific requirements: electrical continuity is essential, but it is also necessary to preserve signal quality during rotation.

Analog, digital, and power signals: different needs

An analog signal represents a physical quantity through a continuous value, for example, a 0–10 V voltage or a 4–20 mA current. Superimposed noise can alter the measurement, where noise is defined as an unwanted electrical disturbance that superimposes on the useful signal, modifying its voltage or current. In a machine, this can be generated, for instance, by motors, inverters, or electrical switching. Inside the slip ring, even small variations in the contact between brushes and rings can contribute to signal perturbation. The effect of cable and contact resistance, on the other hand, depends on the circuit. 4–20 mA connections are generally less sensitive to resistive drops compared to voltage signals, provided the power supply maintains the necessary operating margin. Digital signals encode information into discrete states and tolerate a certain amount of noise. However, if the receiver’s margins are exceeded, communication errors can occur. Therefore, there is no absolute superiority of analog or digital: what matters is the interface, the speed, and the operating environment. Power circuits have a distinct function, which is to feed loads, and require close attention to current, voltage drops, and heating.

Electrical noise and crosstalk: why the path matters

During rotation, variations in contact resistance can introduce disturbances. Added to these are interferences from nearby motors, inverters, and circuits. Crosstalk is the unwanted coupling through which one circuit disturbs another. In high-speed digital connections up to 100 Mbps, like Ethernet, impedance, attenuation, and signal reflections also become critical. The slip ring must therefore be evaluated as part of the entire connection, along with cables and connectors. Circuit layout, maintaining twisted pairs, and properly connected shielding all contribute to preserving communication integrity.

The Celco approach: custom contacts and configuration

Celco markets standard slip rings and also develops custom ones based on currents, signal types, rotation speeds, and environmental conditions. This analysis allows us to define a solution that is perfectly consistent with the machinery and the connections to be established. When choosing contact technology, pairings like gold-on-gold can facilitate low electrical noise; silver-based solutions must be evaluated according to the load and operating conditions. The choice must be completed with wiring suitable for the protocol and an internal layout that minimizes the coupling between power and data. Materials, cables, and shielding for the specific configuration must be agreed upon with the technical department: the contact metal alone does not determine compatibility with an industrial network.

Do you need a hybrid slip ring for power and signals?

A hybrid power and signal slip ring allows you to combine power supply and communication within the same rotary assembly. To define it correctly, you need to specify voltages and currents, number of circuits, signal type, protocol, transmission speed, and cable length, in addition to mechanical and environmental constraints. Contact Celco’s technicians to evaluate your project. Sharing these data right from the early stages allows us to identify the right configuration and the necessary verifications to seamlessly integrate the slip ring into your automation system.

Preventive Maintenance of Slip Rings: Reducing Unexpected Downtime

A rotary electrical slip ring transfers power and signals between stationary and rotating parts. The optimal continuity of this connection contributes to the proper functioning of the machine: wear, contamination, or contact anomalies can compromise power supply and communication. Preventive maintenance of slip rings helps identify problems before they cause an unexpected shutdown. Inspection intervals depend on the model, service hours, speed, and operating environment. The baseline reference is the manufacturer’s maintenance schedule, which should be supplemented by observations gathered during use.

Sealed and Inspectable Slip Rings: When Can They Be Opened?

Before intervening, it is necessary to identify the type of component. For slip rings declared “maintenance-free,” the user is not normally required to perform periodic operations on the internal contacts. However, the external checks indicated by the manufacturer remain necessary, such as inspecting fastenings, cables, and enclosure integrity. “Sealed” and “maintenance-free” are not synonymous: a protected enclosure may provide access for servicing. Conversely, the presence of screws does not automatically authorize disassembly. For inspectable models, opening must exclusively follow the manual and be performed by qualified personnel while the machine is stopped, energy sources are isolated, the absence of voltage is verified, and restarts are prevented (locked out).

What Warning Signs Should Be Monitored?

Measurement fluctuations, intermittent interruptions, and new communication errors deserve attention, especially when they repeat at specific positions or rotation speeds. Unusual noises, vibrations, anomalous temperature increases, or overheating odors also require verification. These symptoms do not automatically prove a slip ring failure: the root cause may also lie in wiring, connectors, alignment, or connected devices. Recording when the anomaly appears, along with the speed, load, and operating hours, aids in the diagnosis. Signs of burning or overheating require a safe shutdown and a technical evaluation before resuming service.

Inspection and Cleaning: Protecting Brushes and Rings

When the manual permits internal inspection, checks should focus on residue accumulation, brush wear against prescribed limits, and the condition of the rings, connections, and insulators. Grooves, irregular deposits, or traces of overheating must be reported. Conversely, a uniform patina on the rings can be normal for certain technologies and should not be removed indiscriminately. The dust generated by wear can be conductive. Where specified by the manual, it must be removed by vacuuming (not blowing) using suitable equipment, carefully avoiding impacts on the rings and contacts. Do not use compressed air, abrasives, solvents, or lubricants without explicit instruction: they can scatter residues, damage surfaces, or alter the device’s operation. The correct procedure always depends on the specific model in use.

Celco Design and Maintenance Manual

The lifespan between one intervention and the next is built directly into the design phase. Celco Profil develops its solutions by considering currents, signals, speeds, and environmental conditions—parameters that guide the selection of the slip ring and help limit stress and wear in the intended application. To determine when to open the component, which checks to perform, and how to clean it, you must follow the instructions for your specific configuration. Request the updated use and maintenance manual from Celco, providing the model, serial number (if available), and operating conditions. This will allow you to schedule interventions precisely according to the guidelines provided for your slip ring.