{"id":52162,"date":"2019-11-02T00:00:00","date_gmt":"2019-11-01T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/obzor-sovremennyh-protokolov-v-sistemah-promavtomatiki"},"modified":"2020-02-18T13:59:50","modified_gmt":"2020-02-18T10:59:50","slug":"obzor-sovremennyh-protokolov-v-sistemah-promavtomatiki","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/obzor-sovremennyh-protokolov-v-sistemah-promavtomatiki","title":{"rendered":"Overview of modern protocols in automation systems.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

\"Overview
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In the previous publication<\/a><\/noindex> we discussed how buses and protocols operate in industrial automation. This time, we will focus on modern working solutions: let's look at which protocols are used in systems around the world. We will examine technologies from German companies Beckhoff and Siemens, Austrian B&R, American Rockwell Automation, and Russian Fastwel. We will also explore universal solutions that are not tied to specific manufacturers, such as EtherCAT and CAN.\u00a0<\/p>\n

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At the end of the article, there will be a comparison table with the characteristics of the EtherCAT, POWERLINK, PROFINET, EtherNet\/IP, and ModbusTCP protocols.<\/p>\n

<\/a><\/noindex><\/p>\n

We did not include the PRP, HSR, OPC UA protocols and others in the review, as there are already excellent articles by our engineering colleagues on Habr that deal with the development of automation systems. For example, \u201cPRP and HSR Seamless Redundancy Protocols\u201d<\/a><\/noindex> and \u201cIndustrial Protocol Gateways on Linux. Build It Yourself\u201d<\/a><\/noindex>.<\/p>\n

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To start, let's define the terminology: Industrial Ethernet = industrial network, Fieldbus = field bus. In Russian industrial automation, there is often confusion in the terminology regarding the field bus and the lower-level industrial network. These terms are often combined into a vague single concept known as the \u201clower level,\u201d which is referred to as both a field bus and a lower-level bus, although it may not be a bus at all. <\/p>\n

Why is that?<\/b>This confusion is likely due to the fact that in many modern controllers, the connection of input\/output modules is often realized using a backplane or physical bus. This means that some bus contacts and connectors are used to combine several modules into a single node. However, these nodes can, in turn, be connected to each other via either an industrial network or a field bus. In Western terminology, there is a clear distinction: a network is a network, and a bus is a bus. The first is denoted by the term Industrial Ethernet, the second by Fieldbus. In this article, these concepts are suggested to use the terms 'industrial network' and 'field bus' respectively.<\/p>\n

The EtherCAT industrial network standard, developed by Beckhoff<\/h2>\n

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The EtherCAT protocol and industrial network is arguably one of the fastest data transmission methods currently available in automation systems. EtherCAT is successfully used in distributed automation systems where the interacting nodes are spread over a large distance.<\/p>\n

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The EtherCAT protocol uses standard Ethernet frames for transmitting its telegrams, ensuring compatibility with any standard Ethernet equipment, and in essence, data reception and transmission can be organized on any Ethernet controller with the appropriate software.<\/p>\n

\"Overview
\nBeckhoff controller with a set of input-output modules. Source: www.beckhoff.de<\/a><\/noindex><\/i><\/p>\n

The protocol specification is open and available, but only within the framework of the development association \u2014 EtherCAT Technology Group.<\/p>\n

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Here's how EtherCAT works (the spectacle is mesmerizing, like playing Zuma Inca):<\/p>\n

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\r\n \"Play\r\n
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The high speed of communication in this protocol \u2014 measured in microseconds \u2014 is achieved by the developers abandoning the exchange of telegrams sent directly to specific devices. Instead, a single telegram addressed to all devices simultaneously is sent into the EtherCAT network, where each subordinate information gathering and transmission node (often called a field device) retrieves the data intended for it 'on the fly' and inserts data it is ready to exchange into the telegram. This telegram is then sent to the next subordinate node, where the same operation occurs. After passing through all field devices, the telegram returns to the main controller, which implements the control logic based on the data received from the subordinate devices, again interacting via telegrams with subordinate nodes that issue control signals to the equipment.<\/p>\n

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The EtherCAT network can have any topology, but it will always function as a ring \u2014 due to the use of full-duplex mode and two Ethernet connectors. Thus, the telegram will always be transmitted sequentially to each device on the bus.<\/p>\n

\"Overview
\nSchematic representation of the EtherCAT network with multiple nodes. Source: realpars.com<\/a><\/noindex><\/i><\/p>\n

Incidentally, the EtherCAT specification does not impose restrictions on the physical layer 100Base-TX, so the protocol can be implemented based on gigabit and optical lines.<\/p>\n

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Open industrial networks and the PROFIBUS\/NAT standards from Siemens<\/h2>\n

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The German company Siemens has long been known for its programmable logic controllers (PLCs), which are used worldwide.<\/p>\n

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Data exchange between nodes in an automated system controlled by Siemens equipment is implemented both via the fieldbus called PROFIBUS and through the industrial network PROFINET.<\/p>\n

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The PROFIBUS bus uses a special two-wire cable with DB-9 connectors. Siemens's version is purple, but we have encountered others in practice :). To connect multiple nodes, the connector can join two cables. There is also a switch for the terminal resistor. The terminal resistor must be enabled on the end devices of the network to indicate that this is the first or last device, and after it, there is nothing but darkness and emptiness (all rs485 work this way). If the resistor is enabled on an intermediate connector, the following section will be disconnected.<\/p>\n

\"Overview
\nPROFIBUS cable with connectors. Source: VIPA Controls America<\/a><\/noindex><\/i><\/p>\n

In the PROFINET network, a twisted pair equivalent is used, usually with RJ-45 connectors, and the cable is colored green. If the PROFIBUS topology is a bus, then the topology of the PROFINET network can be anything: a ring, a star, a tree, or all of these combined.<\/p>\n

\"Overview
\nSiemens controller with connected PROFINET cable. Source: w3.siemens.com<\/i><\/p>\n

There are several bus communication protocols for PROFIBUS and the PROFINET network.<\/p>\n

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For PROFIBUS:<\/p>\n

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    \n
  1. PROFIBUS DP \u2014 this protocol implementation implies communication with remote subordinate devices; for PROFINET, the corresponding protocol is PROFINET IO.<\/li>\n
  2. PROFIBUS PA \u2014 is essentially the same as PROFIBUS DP, but is used for explosion-proof data transmission and power supply (analog of PROFIBUS DP with different physical properties). There is currently no explosion-proof protocol analogous to PROFIBUS for PROFINET.<\/li>\n
  3. PROFIBUS FMS \u2014 is intended for data exchange with systems from other manufacturers that cannot use PROFIBUS DP. The PROFINET equivalent of PROFIBUS FMS is the PROFINET CBA protocol.<\/li>\n<\/ol>\n

    <\/p>\n

    For PROFINET:<\/p>\n

    <\/p>\n

      \n
    1. PROFINET IO;<\/li>\n
    2. PROFINET CBA.<\/li>\n<\/ol>\n

      <\/p>\n

      The PROFINET IO protocol is divided into several classes:<\/p>\n

      <\/p>\n