“In a wide range of Industry 4.0 and Industrial Internet of Things (IIoT) applications, from robotics and material handling to food and beverages, increasingly compact motor controllers are used. However, as controllers shrink, it becomes challenging for designers to simply and cost-effectively route and connect power and data signals while ensuring electromagnetic compatibility (EMC) and operator safety.
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Author: Jeff Shepard
In a wide range of Industry 4.0 and Industrial Internet of Things (IIoT) applications, from robotics and material handling to food and beverages, increasingly compact motor controllers are used. However, as controllers shrink, it becomes challenging for designers to simply and cost-effectively route and connect power and data signals while ensuring electromagnetic compatibility (EMC) and operator safety.
Advanced open source interfaces such as the High Performance Interface Digital Servo Link (Hiperface DSL) and Single Cable Solution (SCS) Open Link have emerged that facilitate simultaneous connection of power and data signals using a single compact connector. This simplifies connections, but makes the quality, design and performance of the connector extremely important to ensure signal integrity, electromagnetic compatibility and IP20 compliance with touch and intrusion requirements.
This article briefly introduces the Hiperface DSL and SCS Open Link interfaces, then discusses the electrical and mechanical requirements for a connector mechanism capable of carrying both power and data signals in space-constrained environments. It concludes with an introduction to Weidmüller’s hybrid motor control connectors and shows how they can be used to meet these requirements.
What are Hiperface DSL and SCL Open Links?
The move to Hiperface DSL and SCS Open Link is to put power and data on the same connector to save space, reduce cost, and simplify the design of high-performance motor controllers (Figure 1). Both are based on RS-485.
Figure 1: Hyperface DSL and SCS Open Link Hybrid Pluggable Connectors Save Motor Drive PCB Space and Simplify Connections. (Image credit: Weidmüller)
Hiperface DSL is a single-cable digital protocol that includes two shielded wires for bidirectional communication and encoder power, motor power, and motor brake wires (Figure 2).
Figure 2: A basic Hiperface DSL compatible cable consists of three parts: power (three-phase power, large brown block in black, and ground, brown block in yellow/green), individually shielded motor brake pair (black in black small brown blocks) and individually shielded data pairs for digital data transmission (brown blocks in blue and brown blocks in gray), all contained within a single shielded cable. (Image credit: Weidmüller)
The Hiperface DSL has a data transfer rate of 9.375 megabaud (MBaud) and cable lengths of up to 100 meters (m) between the motor controller and the motor. There are two ways of transmitting data on the Hiperface DSL; looping as fast as possible under signal and noise conditions, or synchronizing with the controller clock. The Hiperface DSL protocol includes several important functions:
• Capable of synchronizing position and rotational speed information from encoders with cycle times as short as 12.1 microseconds (μs).
・ The maximum cycle time for safe position transmission of the motor feedback system is 192 μs.
• Complies with IEC 61508 Safety Integrity Level (SIL) 2, enabling redundant transmission of safe positions for motor feedback systems with a maximum cycle time of 192 μs.
• Complies with SIL 3 requirements of IEC 61508 when used in a suitable motor feedback system.
• Two-way general data transfer with bandwidths up to 340 kilobaud (kBaud) for transferring parameters including Electronic type tags for storing motor controller data and electronic type tags for motor feedback systems.
・A separate channel carrying data from external motor sensors (acceleration, torque, temperature, etc.) connected to the motor feedback network via the Hiperface DSL sensor hub protocol.
The SCS Open Link Motor Feedback Interface is also designed to support bidirectional data transfer between the motor and controller, including encoder data at rates up to 10 MBaud. It supports two-wire and four-wire implementations. The SCS Open Link is optimized for Industry 4.0, especially for emerging IIoT applications such as motor condition monitoring and predictive maintenance.
Like the Hiperface DSL, the SCS Open Link is certified up to SIL 3. In addition, the SCS Open Link complies with the functional safety requirements of EN ISO 13849 Performance Level e (PLe), Category 3. These single-cable solutions meet the functional safety requirements of IEC 61508-2: 2010 and IEC 61784-3: 2017.
Connector Challenges for Hiperface DSL and SCS Open Links
For reliable operation of Hiperface DSL and SCS open links, a good shielded connection is required between the motor with encoder and the drive. The use of plug-in connectors and connection terminals to minimize the number of interfaces helps to achieve a good shield connection. It is also necessary to use continuous and shielded cables between the motor and encoder and drive. A shielded cable with two plug-in connectors, one optimized for connection to the motor and one to the drive, provides an economical approach and is implemented in Hyperface DSL and SCS open links.
In addition to using shielded cable, the shield needs to be properly terminated at both ends of the cable. Use a plug-in circular connector (usually an M23 circular connector, Figure 3) with a metal housing on the motor side of the interconnection.
Figure 3: Both Hiperface DSL and SCS Open Link support cable lengths of up to 100 meters between the motor and the drive; the motor is connected on the left and the hybrid plug-in connector for the motor controller is on the right. (Image credit: Weidmüller)
To control costs, the plug connectors on the drive side of the interconnect do not need to have metal housings. The physical design of drive connectors is non-standardized, so drive designers need to be careful when developing their own connectors to meet performance requirements while readily connecting to printed circuit boards to simplify connections and minimize connector cost. With proper cable design and assembly, and good EMI shielding practices, cable lengths of up to 100 meters can be achieved.
3-in-1 connector solution for power, signal and EMC
While it is possible to spend time developing a connector design, few motor drive designers have the experience or time to grasp the nuances of connector design despite the requirement to achieve the best possible performance. Instead, they can turn to companies like Weidmüller, which have looked at these problems and come up with some effective solutions.
For example, its OMNIMATE Power Hybrid Connector is a 3-in-1 solution that includes signal, power and EMC functions, enabling Hiperface DSL and SCS Open Link protocols while saving space on motor driver PC boards and control cabinets. The connector is available in several configurations, including six-position (Figure 4, left), seven-position, eight-position, and nine-position (Figure 4, right).
Figure 4: The OMNIMATE Power Hybrid Connector is a 3-in-1 (Power, Signal, EMC) solution with a self-locking flange (red) in the middle. They have six (left), seven, eight or nine (right) positions. (Image credit: Weidmüller)
These hybrid connectors include power and signal contacts with 7.62 millimeter (mm) pitch push-in wire connections and meet IEC 61800-5-1 and UL 1059 Class C 600 Volt (for power contacts) requirements.
The connector has several practical design features needed to ensure a reliable connection. First, they have good isolation between the encoder and motor power connections to minimize EMC problems. Second, the arrangement of the various signal and power connections has also been carefully considered. For example, “neutral” connections like protective earth (PE) are in the middle, and signal and data connections for encoder lines and motor brake lines are placed symmetrically and laterally.
For ease of use, a one-handed, tool-less, self-locking, snap-in interlock mechanism reduces installation and maintenance time. Interlocking also reduces space requirements by one pitch width compared to other solutions. The 30˚ cable entry angle on the shield saves 10 centimeters (cm) of space between rows, reducing solution size.
Effective Use of OMNIMATE Power Hybrid Connectors
To get the most out of OMNIMATE Power Hybrid Connectors, proper cable assembly methods and shield termination are necessary to control EMI and ensure system reliability. Though thoughtfully designed, the OMNIMATE Power Hybrid is still a single-cable interface, so the power and signal lines are still relatively close together. Therefore, good design practice requires ensuring a low impedance connection between the cable shield and the connector. OMNIMATE contains a shield connection plate with pluggable spring contacts, which is particularly useful here. This provides a shockproof shield connection for the drive and secures the shield braid connection of the power and encoder cables (Figure 5). Providing the largest possible contact surface for the shield connection is an optimal solution.
Figure 5: An example of a low impedance shield connection between a single cable and a pluggable hybrid connector solution using a metal cable tie. (Image credit: Weidmüller)
There are several ways to connect the inner and outer shields to the shield connection plate. These options include various combinations of metal cable ties and hose clamps, which are arranged to secure the connection as close to the signal connections as possible (Figure 6).
Figure 6: There are several ways to connect the cable shield to the OMNIMATE Hybrid Power Connector, including using metal cable ties and hose clamps. (Image credit: Weidmüller)
The spring-loaded mechanical design provides the motor controller designer with maximum freedom to place the shield connection on the heat sink or directly on the printed circuit board, ensuring a reliable shock-resistant surface contact area.
Performance testing and safety
Once the design is complete and the cable assembly is produced, it is important to measure the effectiveness of the cable shielding. For example, the KS04B measurement method according to VG95373-41 “Electromagnetic Compatibility of Equipment – Measurement of Shielded Cables and Shielded Protective Cable Conduit” is useful for determining the influence of the contact point on the shielding braid and sockets, plugs and the shielding itself quality is useful. This measurement method is limited, but it is useful for comparing and evaluating the effectiveness of different shielding and shielding contact styles (Figure 7). Limitations of the KS 04 B measurements include the standardized cable length of only 1 meter and the use of a 50 ohm (Ω) system (regardless of actual cable impedance).
Figure 7: Comparison of insertion loss for three shield connection methods according to the VG95373-41 standard, the directional lines (red) represent typical expected values. (Image credit: Weidmüller)
These pluggable connectors meet the IP20 safety standard and, when wired correctly, are safe for operators. However, there are bulk capacitors in a typical motor controller that, if not managed properly, can cause an electric shock to the operator. Capacitors must be discharged and free of Voltage when repairs are made. Although IP20 rated, operators are still advised to wait a few minutes for the capacitors to discharge before touching the connectors. Finally, these open hybrid connector designs allow operators to immediately see and verify that all cables are undamaged and properly connected.
Epilogue
In a compact, high-performance motor controller, the move to a single hybrid interconnect system to transmit power and data can make it difficult for designers to support EMC and ensure reliable operation, as well as operator safety. However, with the well-designed 3-in-1 power-data hybrid plug connector solutions described in this article, they support protocols like Hiperface DSL and SCS Open Link, while also providing reliable EMC It is shielded and meets IP20 safety standards.
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