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Industrial Ethernet Explained
Implementing Ethernet Networks on the Factory Floor: Protocols and Connectivity
Ethernet vs. Industrial Ethernet
Modern manufacturing and material flows are increasingly automated. Advances in robotics and sensor technologies are driving the automation of a wide variety of tasks. To connect the large number of devices necessary to monitor and control complex manufacturing processes, engineers are turning to Ethernet due its high speed, throughput, unlimited address space and broad selection of industrial Ethernet equipment and cabling.
Industrial Ethernet is the same Ethernet used in homes, offices and data centers with two important differences:
- An industrial Ethernet network must contend with a myriad of hazards ranging from extreme temperatures and vibrations to corrosive chemicals and electrical interference from large motors. To mitigate the impact of these factors on network performance and reliability, an industrial Ethernet network is implemented using ruggedized equipment and cabling designed specifically for harsh environments.
- In industrial automation applications, Ethernet is supplemented by protocols that handle the time-sensitive, event-driven communication between controllers and field devices. For example, if a machine jams, the problem must be alerted and acted on immediately. Examples of industrial communication protocols designed to work with Ethernet include PROFINET®, EtherNet/IP® and EtherCAT®.
What are M12 Industrial Ethernet Cables?
M12 cables are designed for hostile environments that are sometimes subject to extreme temperatures, vibration and moisture, including corrosive chemicals. They are designed to ensure a secure, reliable connection between field devices and controllers and between controllers and network switches. M12 cables are essential in washdown environments in food, beverage and pharmaceutical facilities where hot water and chemicals are used to clean and sanitize surfaces. They are also ideal for applications such as railway rolling stock where shocks and random vibrations are common.
M12 Cable Jackets
The jacket on an M12 cable is typically rated CMR, meaning it is suitable for general use including cable runs in riser spaces (between floors). Cables may also carry a CMP rating, which indicates a plenum-rated cable that can be used in plenum spaces, such as cold air returns and spaces above a suspended ceiling.
M12 cables designed for harsh environments use solid copper conductors and a tinned copper drain (ground) wire. The corrosion protection provided by the tinned copper extends the life of the M12 cable, particularly in wet or humid locations or environments subject to high temperatures.
|M12 X-Coded Connector||IP-68 Rated M12 Connector||Right-Angled M12 Connector|
What is tinned copper?
Tinned copper wires are coated with a thin layer of tin, which protects the wire against oxidation and corrosion. Tinned copper is just as conductive as bare copper wire but has the advantage of lasting up to 10 times longer in environments susceptible to high temperatures, humidity or frequent exposure to water.
M12 Connectors and Connector Coding
M12 connectors are circular nickel-plated or plastic connectors with a 12mm locking thread. They provide a tight seal against moisture and are ideal for high vibration applications such as an assembly line.
To avoid the potential for damage resulting from incorrect mating, M12 connectors are letter coded. Each letter refers to a different connector shape and sometimes pin count. Coding may also indicate the performance and construction of the cable. For example, X-Coded cables have aluminum-Mylar shielding and are capable of data transmission speeds up to 10 Gbps.
|a-Coded||Sensors, actuators, Ethernet||
Most common type of connector
1 Gbps (Cat5e) networks
|b-Coded||Fieldbus (e.g. PROFIBUS)||3-5 pins|
|c-Coded||AC powered sensors and actuators||
3-4 pins (230V)
5-6 pins (60V)
|d-Coded||Ethernet, PROFINET, EtherNet/IP and EtherCat||
100 Mbps (Cat5) networks
Can support PoE
|k-Coded||AC power for motors, drives||AC supply up to 12A/630V|
|l-Coded||PROFINET DC power||DC supply up to 16A/63V|
|m-Coded||AC power||AC supply up to 8A/630V|
|p-Coded||AC power||5-pin (230V)|
|s-Coded||AC power for motors and motor operated devices||
AC supply up to 16 A/630V
Replacement for C-Coded
DC supply up to 12 A/60V
Replacement for A-Coded
10 Gbps (Cat6a) networks
Cameras or high-speed data acquisition
Most existing 100 Mbps and 1 Gbps industrial Ethernet networks use A and D coded cables, For new, high-speed Ethernet installations, X-Coded cables are the preferred choice and provide a degree of future proofing. The pins for each twisted pair in an X-Code cable are separated by a cross configuration in the connector, which helps to reduce crosstalk and maintain signal integrity.
What is the difference between an M8 and M12 connector?
M8 cables are used to connect PLCs, I/O boxes and sensors and feature a small, circular 8mm thread screw-style connector designed to remain watertight even when submerged. M12 connectors have a 12mm thread and are used for sensors, actuators, Fieldbus and industrial Ethernet. M12 pin counts range from 3 to 17 so it's important to know what your application requires. Industrial Ethernet typically requires 8 pins and Fieldbus uses 4 or 5 pins.
Cable IP Rating
A cable's Ingress Protection (IP) rating refers to its ability to resist liquids and solid particulates. The first number after the "IP" refers to protection against solids and ranges from zero (no protection) to 6 (complete protection). The second number indicates the degree of protection against liquids and ranges from zero to 8. IP67 and IP68 rated cables are considered "waterproof". An IP67 cable rating indicates that the cable and connectors are dust proof and can be immersed in water 1 meter deep for up to 30 minutes. An IP68 cable can be immersed in water 1-3 meters deep for an indefinite amount of time.
In an industrial setting where cabling may run in close proximity to large motors and other sources of electromagnetic interference (EMI), an overall foil shield with unshielded twisted pairs is a common choice, particularly for high-speed 10 Gbps networks. F/UTP cable is very much like common UTP cable, with the addition of aluminum Mylar foil underneath the outer cable jacket.
Most M12 connectors use a simple screw-on latching mechanism. A threaded nut on the connector is mated with a corresponding set of threads on the port.
Other forms of latching include:
- Push-pull: A male connector is pushed into a female receptacle and locks with an audible click, indicating that a good connection has been established.
- Bayonet: A mating design that uses pins on the receptacle and ramps on the plug for quick connect and disconnect.
Ethernet in Industrial Networks
Fieldbus vs. Ethernet
For the past decade, industrial automation has been dominated by fieldbus, a distributed, real-time control system for programmable logic controllers and field level devices such as sensors, switches and actuators. Devices on a fieldbus can be connected in a daisy chain fashion using inexpensive two-wire cable, reducing the number of cables and the overall cost of cabling.
Driven by the rapid adoption of factory automation, fieldbus is used in approximately half of existing implementations. However, in recent years Ethernet has made significant inroads into the fieldbus installed base, accounting for 65% of new installations compared to only 28% for fieldbus.
Probabilistic vs. Deterministic Communication
Standard Ethernet is probabilistic. It is a "best effort" technology with no guarantee of delivery. An Ethernet network relies on the assumption that devices will probably not communicate at the same time and if they do, they will detect the collision, back off for a period, and then retransmit their data. In IT networks, an occasional short delay in the arrival of a data packet is generally not a problem. By contrast, industrial Ethernet networks must be both probabilistic and deterministic. The network must know with certainty that an event will occur in a predictable amount of time. In a bottling plant, when liquid reaches the top of a bottle, the fill operation must stop. The event ("bottle is full") and response ("stop filling") must occur on time, every time.
What are latency and jitter in industrial automation applications?
In consumer and enterprise networks, periodic delays are expected and mostly acceptable. In factory automation, time-sensitive operations like motion control must be predictable and repeatable. Latency is the time taken for data to travel from one point to another on a network. It can also mean the time taken to complete a roundtrip. In a time sensitive network where devices must sense and take action in "real-time", latency must be low and guaranteed. Variation in latency is called jitter and must also be kept to a minimum.
Are communication protocols like PROFINET competitors to Ethernet?
In the 7 Layer OSI Model, the Ethernet standard occupies Layers 1 and 2 and is concerned with communication between nodes on a network and the electrical and mechanical aspects of physical links. PROFINET is built on top of Ethernet and resides at the Application Layer (Layer 7) where end-user applications interact with network services. It uses Ethernet and other transport layer protocols (TCP/IP and UDP/IP) for non-time critical tasks, such as device configuration and diagnostics.
PROFINET-based network time-sensitive deterministic tasks requiring precise control, low latency and minimal jitter, PROFINET provides two additional channels:
- PROFINET RT handles time-critical communication between controllers and devices. It uses a field in the Ethernet frame called EtherType to bypass normal TCP/IP processing, which would introduce latency and variability. PROFINET RT is faster and more predictable than standard Ethernet and is used for almost all communications.
- For the most time-critical data exchanges, PROFINET IRT ("Isochronous Real-Time") modifies Ethernet traffic-switching rules to prioritize and synchronize this traffic, reducing jitter to less than 1 millisecond.
Ethernet/IP and PROFINET are the most common communication protocols, followed by EtherCAT and Modbus (RTU/TCP).
Industrial Communication Protocols
A number of industrial protocols use Ethernet as the physical (Ethernet PHY) and data link layers for automation and control systems. At lower levels where controllers, sensors and actuators need fast and predictable data communication, standard Ethernet data handling must be modified to meet low latency and jitter requirements.
Nowadays, the choice of protocol is likely to be one of the following. Open, industry-standard protocols make it easier to integrate devices from different manufacturers and can be implemented using off-the-shelf industrial-grade Ethernet switches and cabling.
PROFINET (Process Field Net) is an Ethernet-based Layer 7 protocol for communication between PROFINET-enabled controllers and devices on an industrial network. PROFINET uses standard, unmodified Ethernet as its communications medium, allowing other Ethernet-based protocols to coexist on the same network. It can use TCP/IP and UDP/IP communication for non-time critical tasks such as parameterization and device configuration. For time critical communication, PROFINET uses a real-time channel (PROFINET RT), bypassing normal Ethernet packet processing which can take a variable amount of time. In the rare cases when high-speed, deterministic communication is critical, the PROFINET IRT channel can be used to prioritize PROFINET traffic over all other traffic on the network.
EtherCAT (Ethernet for Control Automation Technology) is an open real-time Ethernet network developed by Beckhoff and supported by the members of the EtherCAT Technology Group. EtherCAT typically implements a ring topology in which one device is the master and all others are slaves. Data frames are sequentially routed to all nodes and each node can add or remove data from the frame before forwarding it to the next device in the ring. Synchronization is achieved through use of a distributed clock system and time-stamping of data frames by each device.
The Modbus communication protocol is the oldest and most widely used protocol for process control and Supervisory Control and Data Acquisition (SCADA). Several versions of the Modbus protocol exist for serial (RS-232, RS-485, RS-422) and Ethernet implementations. Modbus messaging on Ethernet is based on a client-server model in which any device acting as a client an issue commands to a server device (or broadcasts to all devices) and the server device responds by taking the action requested (e.g. open a valve) or providing the information requested (e.g. temperature, flow rate).
EtherNet/IP (in this case, IP stands for "industrial protocol") is an industrial networking standard that uses standard off-the-shelf Ethernet infrastructure and tools. It uses Common Industrial Protocol (CIP), and can be combined with TCP/IP or UDP/IP to implement control applications. In a TCP/IP implementation, devices will acknowledge receipt of a data packet. Continuous data collection applications (e.g. a flow meter reporting status) use UDP/IP, which does not require an acknowledgement.
Do PROFINET and Ethernet/IP require a special type of Ethernet cable?
PROFINET®, EtherNet/IP® and other communication protocols use industrial-grade versions of the same category cabling found in an Ethernet-based IT network. If the equipment you are connecting is capable of 10 Gbps, use Cat6 or Cat6a. If the equipment will be potentially subject to vibration, water or corrosion, use M12 X-Coded cable. Industrial-grade armored fiber optic cable can also be used for high-speed and network backbone connections (e.g. switch to switch, motion control).
Can PROFINET run on a standard Ethernet switch?
PROFINET can use any unmanaged network switch capable of 100 Mbps, full-duplex transmission. The switch should also be designed for an industrial environment with features such DC input power, wide operating temperature range and rugged construction.
Are wireless devices used in industrial automation?
Although wireless represents only 7% of the industrial networking market, it is growing quickly. That growth is expected to accelerate when factories begin to take advantage of technologies such as 5G and mobile robots. Industrial wireless networks must be considerably more reliable than wireless community networks found in airports and coffee shops.
What is the Purdue Model of Control Hierarchy?
The Purdue Model is a framework used in the manufacturing and process industries to group enterprise and industrial network functions into six levels. It was developed in the 1990s and while it remains a useful reference, it is not able to model the hybrid cloud architectures now commonplace in modern manufacturing.
Support for Power over Ethernet
Power over Ethernet (PoE) allows data and power to be delivered over an Ethernet cable at the same time. By eliminating the need for a separate AC power supply, PoE reduces the time, complexity and costs associated with powering a variety of devices in an industrial network, including sensors, cameras and wireless access points (WAPs).
PoE-capable industrial switches can supply up to 100W per port. When a PoE-capable device is connected, the switch will automatically negotiate and supply the required amount of power.
The IEEE P802.3bt standard covering PoE Type 3 (60W) and Type 4 (100W) devices recommends a minimum of Class D Cat5e cabling. For new installations, use LP certified Cat6a cables with solid 23 AWG conductors.
What is LP Certification?
Higher wattage PoE applications generate more heat, particularly when cables are bundled. To address this concern, Underwriters Labs (UL) have introduced a Limited Power (LP) Certification to simplify cable selection. The LP certification means the cable has been tested in situations that might result in higher temperatures, such as large bundles, high ambient temperatures and enclosed spaces or conduits. LP certified cable (look for a cable rating of CMR-LP) can carry the current indicated without exceeding the temperature rating of the cable.
Power Quality & Continuity
For Ethernet switches, controllers and other sensitive electronic devices, the factory floor is an extremely hostile environment. Power surges, voltage sags and power interruptions are commonplace and can result in equipment damage, expensive production stoppages and lost data. To mitigate these risks, UPS systems and surge protectors must be deployed at all levels of the network to avoid power fluctuations and failures.
Extreme temperature and humidity is another challenge for network devices and the power quality systems that support them. Most IT equipment is designed to operate in temperature controlled data centers or office spaces. On factory floors and in warehouses, ambient temperatures can be warmer or colder than the typical workspace. For example, Tripp Lite's extreme temperature UPS systems are designed to operate in non-IT environments where temperature ranges from -40°C to 80°C.
New manufacturing technologies such as collaborative robots and additive manufacturing (3D Printing) have led a dramatic growth in networked devices on the factory floor, many of which run unattended. This in turn creates the need for a smart and connected approach to power quality and power backup to ensure the reliable and safe operation of these processes.
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