Communication Buses in Industrial Environments: Types, Topologies and Installation Recommendations

Industrial communication buses facilitate the exchange of information between devices in factories, production plants and other industrial environments. Buses such as Profibus, Modbus and Profinet enable the integration of sensors, actuators and controllers efficiently and reliably, ensuring real-time data transmission. In this article, we will discuss the types of communication buses most commonly used in industry, their topologies, installation recommendations, and a reflection on the future of wireless communication in these systems.

Types of Communication Buses

1. Modbus RTU and Modbus TCP/IP: Modbus is one of the most widely used protocols and exists in serial (RTU) and Ethernet (TCP/IP) versions. It is an open and low-cost protocol that allows communication between different devices in the same system. However, in Modbus RTU, the transmission speed is limited (typically 9600-115200 bps) and it is not designed for large-scale networks.
2. Profibus: Developed by Siemens, Profibus is a widely used protocol in Europe. Profibus DP is ideal for fast automation networks (up to 12 Mbps) and can handle lengths of up to 1200 metres with high quality cables. Profibus PA, on the other hand, is used in classified areas and provides power to connected devices.
3. Profinet: This Siemens protocol is based on Ethernet and allows transmission speeds of over 100 Mbps. With features such as redundancy and ring topology, Profinet is ideal for critical applications where network availability is essential.
4. EtherCAT: EtherCAT, an Ethernet-based protocol, is noted for its low latency and speed (up to 100 Mbps), making it ideal for real-time motion control applications.
5. CANopen: Based on the CAN (Controller Area Network) protocol, it is common in automotive and industrial applications. It allows a maximum speed of up to 1 Mbps and is ideal for small networks due to its simplicity and low cost.

Network Topologies

1. Bus Topology: Bus topology is the preferred configuration for fieldbuses, such as Modbus and Profibus, due to its simplicity and efficiency. It is especially useful to avoid packet bounce and synchronisation problems. In this scheme, devices are connected in series and require terminators at the ends to avoid signal reflections.
2. Star Topology: Common in Ethernet-based networks such as Profinet and Modbus TCP/IP, the star topology centres around a switch or router that facilitates the connection of devices. Although not the most efficient configuration in terms of cabling, it facilitates diagnostics and expansion.
3. Ring Topology: Used in Ethernet-based industrial networks such as Profinet and Ethernet/IP, this topology allows for high redundancy. In the event of a failure on one leg of the ring, the system automatically reroutes traffic, minimising downtime.
4. Mesh Topology: In industrial environments that require high redundancy and wireless connectivity, such as WirelessHART or ISA100.11a networks, the mesh topology allows each node to act as a repeater. This ensures wide and reliable coverage, especially in hard-to-reach areas.

Installation Recommendations

1. Length Management and Cabling:

• Maximum Length and Cable Section: Keep lengths within the limits recommended by the protocol (100 metres on Ethernet without repeaters and 1200 metres on Profibus). Use repeaters or amplifiers on long networks and select a suitable cable cross-section to avoid voltage drops.
• In Modbus communications, use shielded twisted pair cable. Maximum length 1200 metres. End-of-line resistance of 120 Ohms. Bus topology with a maximum distance in derivations of 30 cm. Avoid star configurations.

2.Protection against Electromagnetic Interference (EMI):

• Shielding and Grounding: Use shielded cables and ground them at one end only to avoid ground loops. This is especially important in high EMI environments.
• Separation Distance: Keep communication cables at least 30-50 cm away from power cables and EMI-generating devices.
• Use of Ferrites: Install ferrites at the ends of cables to block high frequency interference in complex industrial environments.

3. Connectors and Connections:

• High Quality Connectors: Use industrial-grade connectors with IP65 or IP67 ratings for environments exposed to dust, moisture or vibration.
• Avoid Splices: Limit splices in cabling to reduce signal loss. If necessary, use specific connectors for bus cables to reduce signal loss.
• Cable Labelling and Organisation: Clearly label cables to facilitate diagnosis and maintenance, especially in large networks.

4. Surge Protection:

• Surge Suppressors (SPD): Install surge protection devices in the switchboard and on key equipment. Use SPD type 1 for main protection and type 2 or 3 in critical areas.
• Transient Voltage Surge Filter (TVS): Use TVS diodes on sensitive data lines, and gas dischargers in areas exposed to extreme voltage spikes, such as outdoor installations or those exposed to lightning strikes.
• Effective Grounding and Shielding: Ensures proper grounding of all protective devices and shielding, allowing safe discharge of surges.

5. Redundancy in Critical Networks:

• Ring Redundancy: Implements ring configurations in industrial Ethernet networks with switches that allow fast switching (such as RSTP or ERPS).
• Redundant Device Configuration: For critical applications, install redundant devices at key points, ensuring that communication is not interrupted in case of failure

6. Maintenance and Diagnostics:

• Online Monitoring Devices: Use network analysers to monitor critical parameters in real time, detecting signal drops or transmission errors.
• Test Access Points: Add test points to perform diagnostics without the need to dismantle cable runs, facilitating maintenance and troubleshooting.

Conclusion:

A good planning of your communication network in industrial environments is key to guarantee a good service and a correct operation of the whole, in the same way that hydraulic networks or electrical networks are studied and defined.

In practically all the applications that we encounter on a daily basis, there is a communication bus of greater or lesser scale, and it is increasingly important that this operates efficiently and reliably, to guarantee supervision and to be able to deal with possible faults or maintenance that may be required.

With the advent of wireless technologies such as WirelessHART and ISA100.11a, industrial communication systems are expected to become increasingly flexible, secure and easy to install in the future. These protocols enable a mesh topology, where each device can act as a repeater, extending coverage and simplifying installations. Wireless technology will significantly improve equipment connectivity, reducing cost and deployment time in environments with difficult access or device mobility. As wireless networks advance, predictive maintenance and remote management will become even more accessible, driving efficiency and connectivity in the industry of the future.

Prepared by: Manuel García Jiménez