Industrial networks, automation and comparison of various communication protocols

Today, industrial plants must reduce operating costs, maximize capital investments, improve plant operations, and manage assets to stay competitive.

Intelligent precision tools combined with an integrated architecture allow easy access to data – without being on site – data sharing across the company, a high level of process control and more accurate predictive maintenance cycles.

Ethernet and fieldbus are the two main keywords when talking about industrial communication systems. Despite the various developments of intelligent, flexible and complex control systems, the needs of users should not be neglected in industrial communication.

Parallel use

You already know from your computer at home: some programs are not compatible with every operating system, and some do not want to work with others. Here, different operating systems always cause headaches.

In order to avoid this for users of industrial communication systems, there is a standardized testing and certification system that requires manufacturers of field components of industrial Ethernet systems and fieldbus systems to ensure that all their devices can share data and synchronize with each other through a shared network.
When a device does not have such a certificate, it is not certified as equipment.

Main technology for automation

The first step in industrial automation was parallel wiring, where participants were wired separately with the law and control. However, the number of subscribers increased with the increase in the degree of automation, and this led to high wiring costs. Currently, parallel wiring has been widely replaced by cheaper and faster fieldbus systems and Ethernet-based communication networks.

Fieldbus or Ethernet?

Users of industrial communication systems need not worry. Because legacy facilities often need to be updated, expanded, or modernized (or partially modernized), transparent network gateways and compatible Ethernet and fieldbus networks have been a logical development. In practice, special gateways and connection systems have been developed.

What are the advantages of Ethernet?

The needs of users, not only in industrial communication, show a tendency towards the ability to perform more complex tasks in easy ways.
The actual Ethernet data transfer can even be centralized in a single installation system, which offers the user the benefits listed here, among others:

• Only a single cable is laid, which significantly reduces the cost of installation.
• Not only is it easier to maintain, but it is also cheaper to train installation and maintenance personnel.
• Error correction is simplified and shortened. Even on-the-fly error correction is possible without problems.
• All networks have more or less uniform engineering and configuration tools.
• Depending on the configuration, the collected network information can be processed by all the minor components.

Complex structure but simple operation

Industrial communication users also need some time to get used to new systems. Now, depending on the task, separate Ethernet components can be combined, which does not really facilitate the operation.
To meet the needs of users of industrial communication systems, Ethernet networks are built as follows:

• Individual components (slaves) are combined and controlled by a common controller (master).
• Master Hats can communicate with each other using a shared network. However, this is also possible if lateral communication of individual field components is more efficient for information transfer. Basically, this means that it is possible for masters and/or slaves to communicate with each other.

This reduces the load for the main control of the plants, which fully meets the needs of industrial communication users.

Fieldbus basics

Fieldbus systems developed in the 1980s are essential in today’s industry. As a fixed component of complex machines and installations, they are primarily used in production automation. However, this field is also used in process and building automation as well as in automotive engineering.

Sensors and actuators (so-called “field devices”) as well as motors, switches, drives or lamps are connected to programmable logic controllers (SPS) / main and processing controllers using serial and serial feedback buses. . In this way, Fieldbus supports fast data exchange between individual system components even over long distances. Even strong external loads cannot affect the digital signal power transmission system. Since fieldbus communicates only through cables, wiring can be significantly reduced compared to parallel wiring.

A fieldbus task is called a so-called master-slave operation. While the master is responsible for controlling the processes, the slave stations perform minor tasks.

Fieldbuses are different according to their topology (star, line, tree or ring), their transmission media and depending on the type – different transmission protocols (message-oriented method or summarizing frame method). Separate fieldbuses can also be used according to the length of the cable. Access, maximum number of data bytes per telegram and performance range are different. Likewise, additional functions such as alarm control, detection and side traffic between bus participants are not possible for each fieldbus.

Advantages of Fieldbus

• Speed: Fieldbus systems can be programmed and installed more quickly due to reduced wiring costs. Fieldbus communicates through only one cable.
• Reliability: Short signal paths increase access as well as reliability of systems.
• Interference Reliability: They provide more protection against interference, especially in the case of analog values.
• Uniformity: Equipment from different manufacturers can be used and interchanged due to standardized protocols and unified connectivity technology. As such, not all individual components need to be from the same manufacturer.
• Flexibility: Even expansions and changes can be implemented easily and quickly with fieldbuses. In this way, systems can be flexibly adapted to new needs and can be used in the future.

Disadvantages of Fieldbus:

• Complexity: Since a fieldbus represents a complete system, qualified personnel are required to operate it.
• Costs: Unique components in Fieldbus are significantly more expensive.
• Risks in the event of an error in the bus: the guidance system can be separated from the sensors and actuators. To avoid this, if necessary, redundant systems should be used.

Types of communication protocols

Whether it is a simple or complex instrumentation, integrated architecture solutions can be designed using intelligent tools. The following list contains common protocols used in industrial networks:

• Fieldbus Foundation
• Profibus
• DeviceNet
• Modbus
• Hart
• A.S.I
• Wireless

The following are a wide range of services required to design new or retrofit instrumentation systems:

• Feasibility
• Design of P&ID drawings
• Hardware specifications
• Network specifications
• Buy parts
• Installation supervision
• Remote data collection
• Intelligent preventive maintenance
• Operation and maintenance methods

Here are more details on the commonly used protocols:

Fieldbus Foundation

Fieldbus Foundation is a fully digital, serial, two-way communication system that serves as the base-level network in a plant or factory automation environment. This protocol is an open architecture protocol, developed and managed by the Fieldbus Foundation with two different physical media and communication speeds.

• H1 operates at 31.25 kbit/s and is generally connected to field devices. Provides connection and power for standard twisted-pair wiring.
• HSE (High Speed Ethernet) operates at 100 Mbps and generally connects I/O subsystems, host systems, connecting devices, gates, and field equipment using standard Ethernet cabling.

The fieldbus foundation was originally intended as an alternative to the 4-20mA standard, but many delays in its development have prevented it from being used on a large scale, and it has been replaced by other technologies such as Modbus, Profibus and Industrial Ethernet. allowed to include a large installed base. Fieldbus Foundation was developed over many years by ISA, as SP50.

Profibus (industrial fieldbus)

PROFIBUS (PROCESA FieldBUS) is an industrial control network that is used for factory automation, process, motion control and safety networks. Using master/slave architecture, using two-wire network (RS- 485) enables power-free PROFInet is an Ethernet-based version of PROFIBUS designed to connect business-grade systems.

Profibus is standardized under Fieldbus European EN 50 170 standard. It includes two versions, DP and PA.

• PROFIBUS DP (Decentralized Peripherals) is used to operate sensors and actuators via a centralized controller in manufacturing technology, offering many standard diagnostic options.
• PROFIBUS PA (Process Automation) is used in process engineering to monitor measuring equipment through a process control system and is ideal for hazardous areas with the possibility of explosion.

DeviceNet

is a communication protocol used in the automation industry to internally connect control devices for data exchange. It uses (Controller Area Network) as the backbone technology and defines an application layer to cover a wide range of device profiles.

DeviceNet was originally developed by the American company Allen-Bradley (now owned by Rockwell Automation). This layer is on top of the CAN protocol developed by Bosch.

DeviceNet is now managed by the Open DeviceNet Vendors Association (ODVA), an independent organization.

Modbus

is a serial communication protocol released in 1979 by Modicon for use with their PLCs. Modbus enables communication between many devices connected to the same network, for example a system that measures temperature and humidity and communicates the results to a computer. The main reasons for the widespread use of Modbus compared to other communication protocols are:

• This release is publicly available and free
• Industrial network establishment is relatively easy
• It moves raw bits or words without imposing too many restrictions on vendors.

Modbus protocol versions exist for serial port and Ethernet and other networks that support the Internet Protocol suite. For connections via TCP/IP (e.g. Ethernet), there is the latest version of Modbus/TCP. No need to calculate Sam’s check.

Hart

HART (Highway Addressable Remote Transducer) was originated by Rosemount in the late 1980s and became an open protocol in 1990. This protocol was designed to define the traditional analog signaling of 4-20mA, the HART protocol supports two-way digital communication for measurement and process control devices. Applications include remote process variable interrogation, cyclic access to process data, parameter setting, and diagnostics.

HART is an early version of Fieldbus, a digital and industrial automation protocol. The biggest advantage is the fact that it is based on a conventional standard of 4 to 20 mA that serves to transmit analog signals. The existing wiring of the old system can still be used and parallel operation of both is possible.

Due to the standard base of 4 to 20 mA, the HART protocol is one of the most widely used protocols in the industry. Data is transmitted according to the Bell 202 standard using frequency shift keying technology. The HART protocol provides great convenience for users who use the standard 4-20mA protocol and want to use a “smarter” system with a wider range of services.

Different hart states

There are two modes of operation for HART teleportation protocol devices: an analog/digital mode and a multi-drop mode.

In point-to-point (analog/digital) operation, digital signals are applied to the 4 to 20 mA system. In this way, the current of 4 to 20 mA and the digital signal are the valid output values of the device. The sampling address of the device is set to “0”. Only one device can be used in each pair of signal cables. With this, a user-defined signal can be sent as a 4 to 20 mA signal. Other signals are used digitally on a 20.4 mA signal with the HART remote transmission protocol. For example, a pressure display can be sent as a 4 to 20 mA signal, but a wide range of pressures or temperatures can also be sent digitally over the same lines.

Only digital signals are used in multidrop (digital) operation. By doing this, the analog loop current is fixed to 4 mA. In multi-drop mode, more than one device can be operated per signal cable pair. Versions 3 to 5 of the HART protocol have sampling addresses in the range of 1 to 15. HART 6 (and higher) allows up to 63 single addresses. Each device must have its own unique address.

A.S.I

(Sensor Actuator Interface) is used for network sensors and actuators. ASI is a two-wire interface; Power and data. It is based around ProfiSafe [developed from Profibus DP]. ASI Bus was developed by Siemens Automation. It is a 2-wire bus [yellow cable], unshielded, unbroken, ungrounded sensor. The topology may be bus, ring, tree or star up to 100 meters. Power is provided by a floating DC 24V power supply, which can supply at least 8A from the mains. AS-Interface is an open standard based on IEC 62026-2 and EN 50295.

wireless

There is great interest in wireless data communication in industrial processes. In particular, wireless sensors have the following advantages over their wired counterparts:

• Installation costs are reduced by up to 90% by eliminating field wiring.
• Inherent electrical insulation. They do not conduct electrical noise, electrical current surges.
• Quick installation and easy handling
• Communication paths are not corroded, cut, burned, shorted or punctured.

For some time, industrial applications have been successfully implemented using licensed radio frequencies at high costs and with significant administrative burden. With the development of many consumer products using wireless communication technology, the availability of good quality and affordable hardware has improved dramatically over the past few years. Wireless equipment can be divided into three distinct groups.

• High power, high data speed, long range and licensed: commercial radio, TV, military, satellite and SCADA
• Low power, high data speed, license-free short range for home and office: Wi-Fi, office data network, mobile phone (moderate reliability convenience)
• Micro power, low data rate, license-free medium range for industry: process measurement, equipment monitoring, control (high reliability and duty cycle)

It is important to understand the differences between electromagnetic and wireless. A wireless capability developed for one type of application will certainly not apply reliably to a different important application.

Choose your protocol

As shown in the table, each protocol has its own advantages and design considerations, but they all share a common demand. Training project implementation engineers is also essential, as is the use of protocol planning tools, engineering guides, component design recommendations, gate loading, and other design considerations.

Maintenance challenges can be met by training instrument technicians, purchasing the required tools, and planning for job descriptions that cross between the instrument and host systems.

With these conditions met, a combination of wired HART and Wireless HART is usually the best option for projects that aim to simplify and speed up calibration, instrument maintenance, and troubleshooting at the lowest cost.

The HART standard has been in use for decades and many are familiar with the installation, commissioning and maintenance of HART wired devices. These instruments can measure various process variables or inferential variables, but extracting these secondary variables from minute instruments can sometimes be a challenge.

PROFIBUS PA is typically used in facilities with existing PROFIBUS DP installations or projects where the host system has superior support for PROFIBUS protocols compared to FF.

FF is the only wire network that is built from the ground and is used to control and monitor field instruments and valves.

Wireless HART makes sense for process plants adding new measurement points because it doesn’t require wiring the signal to the instruments, and often without power wiring. Once the wireless infrastructure is in place, devices can be added very quickly, and the wiring infrastructure and maintenance required are much lower than in other types of geospatial environments. In many cases, Wireless HART data transmission will be more reliable than wired systems because there are no wires to corrode or accidentally damage.

Wired has traditionally been the standard used for control, but wireless is maturing and becoming more trusted in real-time control depending on the application’s needs. Moving forward, new installations use an integrated combination of wired and wireless technologies.