What are the main industrial protocols for the monitoring of plants?

Created: 11 June 2019 Written by Andrea Cadei

Today many insiders talk about the interconnection of industrial machinery with software and platforms for the management, monitoring and control of plants, but what exactly do they refer to?

Introduction

With this article we try to make some clarity in the Babel of industrial communication protocols, the condicio sine qua non for interconnection and data exchange. In fact, at the basis of the interconnection between a machine and a software, there is necessarily a communication protocol.

In the majority of companies (small, medium or large) the machinery is extremely varied. It often happens to see within company machines of different ages, suppliers, and technologies. This heterogeneity often requires the use of different communication protocols, thus making the interconnection operation complex and not immediate.

Before we take a look at the main industrial protocols, let's see what exactly a communication protocol is.

Definition

A protocol is nothing more than a language with which a machine, an electronic board, software or more generally a device communicates with the outside world. There are hundreds (maybe thousands) of protocols used in computer networks, in electronics, and in industry.

We can think of a protocol as an actual language. Take for example two possible interlocutors: a machine and a plant monitoring software. The only way for the two to exchange information (for example to know the state of the machinery and the number of parts produced) is for them to speak the same language. It goes without saying that speaking the same language (i.e. using the same protocol) is essential to enable machinery, devices and software to communicate with each other.

That said it looks very simple: just choose a common protocol for data exchange and you're done. In practice, however, machinery and software are purchased at different times but above all they are made by different manufacturers and designers. Each manufacturer therefore arbitrarily chooses a protocol for their machinery. Although this choice may be based on a standard protocol, this leads to the proliferation of numerous types of languages in almost every production plant.

The software that exchanges information with the machines in production acts as an interpreter and, therefore, must know all the languages used by the interconnected machines. To complicate things, in some cases not even too isolated, the machinery uses a non-standard protocol, designed by the manufacturer himself. It is as if the machine speaks a language or dialect that nobody else knows. The interconnection software must, therefore, know the new protocol to communicate with that specific machine. Fortunately, in recent years, the trend is to move towards standardized protocols. Having a single industrial protocol suitable for all needs would be ambitious, but being able to have a limited set of industrial protocols would, without doubt, already be an excellent result.

Classification of the main industrial protocols

Never before as in recent years, the industry market is experiencing a strong evolution, favoured both by the use of distributed intelligence and by the need to make different platforms and machinery dialogue.

Let's see, therefore, what are the main protocols that have established themselves also following the industrial revolution that we are experiencing.

EtherNet/IP

It is an open industrial standard that was born in 2000 with the aim of having a protocol on Ethernet able to meet the performance and reliability requirements of the industrial world. It is a complete protocol because it supports the transfer of basic I/O data, cyclic monitoring and status change events [1]. Variables are accessed by name (TAG).

EtherNet/IP is a real-time protocol with discrete performance (relative to the real-time world), which however fits perfectly into the monitoring field.

It is a well established protocol in the American market, a little less so in the European market. It is often used with Rockwell control systems (Allen Bradley PLC).

Profinet IO

Based on standard Ethernet technology, Profinet uses traditional Ethernet to define a network to exchange data, alarms, and diagnostics with PLCs and other industrial devices.

PROFINET IO uses three different communication channels for data exchange with programmable controllers and other devices. The standard TCP / IP channel is used for parameterisation, configuration and acyclical read/write operations. The real-time channel is used for standard cyclic data transfer and alarms. The third channel, Isochronous Real Time (IRT) is the very high-speed channel used for Motion Control applications. ^[2].

Being a real-time protocol, it has high performance that makes it suitable for fast control. Profinet's hardware requirements are often restrictive when you need to use a non-real-time device. A frequent need in the field of monitoring is to connect from a PC with Windows Operating System to the field. In these cases, it is often preferred to rely on another protocol (perhaps even with lower performance).

Profinet is used by PLCs and devices from the Siemens world.

MTConnect

It is an industry standard used for data collection and monitoring on numerically controlled machines (CNC). The protocol only supports reading data and therefore does not allow parameters, recipes or commands to be written. The data is presented in XML format.

The first public demonstration of MTConnect took place at the International Manufacturing Technology Show (IMTS) in Chicago in September 2008. There, 25 industrial equipment manufacturers networked their machine control systems, providing process information that could be retrieved from any web-enabled client connected to the network.^[3].

MTConnect is often available on Mazak, Mitsubishi and Mori Seki CNCs.

Modbus

It is the most long-lived of the protocols presented. It was created in 1979 by Schneider Automation and quickly became a de facto standard. Modbus is implemented on Ethernet networks (ModBus TCP) and on RS 485, 232 and 422 serial lines. ^[4].

In the Modbus protocol, the data are organized in registers that are accessed by address. The register is the smallest entity on which a write and read operation can be performed. In turn, the registers are organised in a series of precise tables:

Input register, for read-only operation on numeric registers.
Holding register, for reading and writing operation on numerical registers.
Discrete input, for read-only operation on Boolean registers.
Coils, for reading and writing operation on Boolean registers.

Although there are alternative protocols that perform better, the ModBus protocol is widely used because it is open source, has a low development cost and requires limited hardware. It does not have high speeds but it is perfectly suitable for monitoring where the required speeds are low.

ModBus is often used by Schneider devices but also on simpler devices such as temperature sensors and for energy monitoring.

OPC-UA

It is an open, multi-platform industrial protocol developed by the OPC Foundation. The name bodes well. UA stands for Unified Architecture.

OPC UA replaces the old OPC, retaining all the functionality of its predecessor. The strength of OPC-UA is undoubtedly its flexibility. In addition to industrial PLCs, it is supported by Windows, Linux, iOS and even Android.

Conclusions

The protocols presented above are nothing more than a very small part of the world of industrial protocols. In this article we have limited ourselves to presenting the main ones, especially from the point of view of monitoring. For completeness of information, in the industrial sector there are other protocols with high reliability and performance (one on all EtherCat) but that do not match with the monitoring of plants.

In conclusion, it is easy to see that there is no better protocol than another. Simply, different protocols adapt to different needs, hardware and project specifications. In order to standardize communication and to go in this direction of language homogeneity, we could consider OPC-UA a protocol that winks at the future thanks to its versatility. In fact, it has also been well received by manufacturers of industrial devices (the latest generation Siemens S7-1500 PLCs natively support OPC-UA-based communication) and at the same time it is supported by the main operating systems.

We have seen how in the industrial world there are many protocols that differ in performance and access modes.

T4SM, thanks to iDaq, its data collection platform, guarantees the interconnection and monitoring of plants in a quick and easy way. iDaq in fact supports many industrial protocols giving also the possibility to interconnect machines with non-standard protocols. Thanks to this, our solutions constitute a single platform for the monitoring of machines of different manufacturers, functionalities, and technologies.

» Contact us on 030 2681510 or at This email address is being protected from spambots. You need JavaScript enabled to view it. to discover the amazing benefits of our solutions.

Sources

[1] https://www.manufacturingtomorrow.com/article/2016/05/5-real-time-ethernet-based-fieldbuses-compared/8044/

[2] https://www.rtautomation.com/technologies/profinet-io/

[3] https://web.archive.org/web/20110727101505/http://mtconnect.org/download/MTConnect%20NEWS%2010_07_08.pdf

[4] http://www.swappa.it/wiki/uploads/Uni/progetto_LR_mcavenaghi.pdf