PROCESS INDUSTRY
Communication is key
ALSO IN CONTROL SYSTEMS!
By Mikkel Smal Bundgaard
Know your communication systems, and avoid typical errors in PROFINET, PROFIBUS, AS-I bus and IO-Link.
In both modern and older control systems, reliable production depends on stable communication between the PLC and actuators or sensors. In practice we see that many downtimes are caused by communication errors. And that the vast majority can be traced back to installation errors, rather than faulty electronics, maintenance or programming.
Four protocols across two levels
PROFINET and PROFIBUS are among the most widely used fieldbus protocols in northern and central Europe, whereas AS-I bus and IO-link are used at the sensor/actuator level.
For maintenance technicians on site, hands-on knowledge of these technologies is one of the fastest shortcuts to recovering from production downtime. When you understand why the technologies behave the way they do, complex errors become significantly easier to identify and solve. This will lead to better installations, faster troubleshooting and in the end, fewer and shorter downtimes, planned or unplanned.
Quick overview of the protocols including most common faults:
PROFINET – Flexible and fast, but open and vulnerable
PROFINET is widely used in many modern control systems and are considered to be the replacement for PROFIBUS. The technology is ethernet based, which gives a high flexibility in design and installation, faster speed and easy integration of industry 4.0 and other secondary services. But it also inherits the vulnerability of ethernet, where EMC, cyber security and overall site infrastructure must be considered.
The most common faults are often caused by:
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Cable and plugs are not installed properly
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Inadequate shielding and equipotential bonding
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Incorrect switch, topology and VLAN settings
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Default or wrong device name
Knowledge of PROFINET, helps you to:
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Start troubleshooting at missing devices in the topology
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Spot wrongly installed plugs
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Check devices for correct naming
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Know the importance of correct shielding and EMC
PROFIBUS – Robust and stable, if installed correctly
PROFIBUS is a well-known technology that is used on many sites today and still installed on newer control systems. Even though the technology is based on the older RS-485 protocol, simplicity and reliability still find uses today.
The system is based on a master to slave principle, and components are daisy chained together. The fieldbus is isolated from other networks, does not involve any consideration on cyber security and overall site infrastructure. It is, however, very susceptible to EMC, cable lengths and overall impedance of the line. Leaving technicians on site surprised when a minor change can topple a whole network.
The most common faults are often caused by:
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Cable and plugs are not installed properly
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Wrong or missing termination
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Long cables or too many devices in one segment
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Inadequate shielding and equipotential bonding
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Dual or wrong addressing
Knowledge of PROFIBUS, helps you to:
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Start by checking the termination, cabling and plugs
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Lower speed on the line
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Measure signal quality with a class 2 master
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Know the importance of correct shielding and EMC
AS-interface – simple system with low amount of data
AS-interface is designed to be a simple and cost-effective communication system, at the actuator and sensor level in a control system.
The system is simple and fast, by combining power and data in the same cable and limiting the data amount to 4 bits. This gives a protocol that is excellent for digital sensors or actuators, that only have a few bits of relevant data. But it is less optimal for analog data, because it must be split up into multiple data packages. Different styles of topology and hardware can be used, but it is very important to stay withing the design guidelines.
The most common faults are often caused by:
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Perforation of flat AS-I cable – especially in acidic environments
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Long drop cables / voltage drops
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Wrong addressing
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Overloaded power supply
Knowledge of AS-interface, helps you to:
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Read error messages on the AS-I master
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Check, cable and plugs, especially for the AS-I flat cable
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Measure voltage drops
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Know when to add repeaters and terminations
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Know the importance of following design guidelines
IO-link – Intelligence and diagnostic, in the field
IO-link is increasingly being used as a supplement or replacement of traditional wiring and AS-I at the actuator and sensor level. It does not work as a fieldbus, but as point-to-point communication between a device and an IO-link master. It is commonly connected via standard length M12 cables and limited by the number of ports on the master. Diagnostics, setup and intelligence must be done in the IO-link master, instead of being centralized in the PLC. Although it is intuitive and easy to do, it is time consuming and harder to maintain.
The most common faults are often caused by:
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Lack of understanding of master port types (Class A / Class B)
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Power supply and load on the master
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Lack of structure in parameter management when replacing devices
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Long cable lengths and incorrect choice of cabling type
Knowledge of IO-link, helps you to:
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Replace sensors without manual re-parameterization
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Advanced diagnostics directly from the field device
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Avoid errors related to power, port types and incorrect cabling
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Can standardize installations and reduce commissioning time
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Improve documentation and traceability in the plant
When knowledge makes a difference
When technicians understand the challenges in communication systems like PROFINET, PROFIBUS, AS-I and IO-link, they achieve:
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Faster and accurate troubleshooting
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Fewer installation errors
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Lower downtime
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Collaboration between technical personnel and IT/Automation personnel
