Industrial Data Flow and Devices

In this chapter, we'll take a close look at the equipment, devices, protocols, and software layers that manage industrial data along its path in the factory. We'll start from the sensors and track the path of data until we reach the edge, which is the external boundary of the I-IoT data flow inside the factory. We'll look at how industrial signals are generated and how they are managed, exchanged, and enriched by passing through the different levels of the CIM pyramid. We'll also consider what the main OT devices that are involved in each level are. The reader will learn about analog to digital conversion and vice versa, sensors and actuators, remote terminal units (RTU), embedded controllers, programmable logic controllers (PLCs), distributed control system (DCS), Supervisory Control and Data Acquisition (SCADA), Historian...

Technical requirements

You will need to have read the previous chapters of this book to understand the concepts presented in this chapter. Knowledge of the following topics is also necessary:

• Networking and the related ISO/OSI model
• The basics of electronic circuits
• Key elements related to computer architecture

The I-IoT data flow in the factory

The following diagram depicts the main pieces of equipment, OT devices, networks, and protocols involved in the I-IoT data flow. These are arranged according to their hierarchical structure in the CIM pyramid, as we have already seen in previous chapters:

I-IoT devices and protocols in the factory

We will emphasize here that this logical schema is not a complete picture of all of the equipment, devices, networks, and protocols that we have in an industrial plant—nor is it the only possible representation of their interactions and interconnections. As we mentioned in previous chapters, there is no such precise and clear-cut separation of functionalities and devices between CIM levels in the real industrial world. Some devices placed in one particular level can be deployed to an upper or lower level with an enlarged or restricted scope...

Measurements and the actuator chain

The devices that measure and act on the process variables are of fundamental importance in implementing a control system. Their values are used by controllers, together with the reference values that are inputted, to generate the control signals. This is outlined in the following diagram, where we have the following:

• Set point (SP): This is the reference and the desired value for a specific process variable
• Controlled value (CV): This is the calculated value for the control variable to fit the reference value
• Process value (PV): This is the measurement of the process value that comes from the process:

Measurement and actuator chain

Let's think about a very simple example. When you turn on your oven, the SP is the temperature that you want to set. The CV is the value of the electric current that is feeding the heating elements of the...

Controllers

We can define controllers as electronic devices that receive digital signals and process them according to a user-defined program for generating other digital signals in the output in a predefined time interval. In this section, we will explain the main types of controllers used in industrial plants. These are microcontrollers, PLCs, and DCSs.

Microcontrollers

A microcontroller is a programmable electronic device that is based on an integrated chip. It includes many of the components needed to make a control system. It can perform different functions autonomously, according to the program that's been implemented. From a computational point of view, a microcontroller is very similar to a microprocessor in that...

Industrial protocols

The reference model for computer networks is the Open Systems Interconnection (OSI) model, which was developed by the International Organization for Standardization (ISO). It is a conceptual model to which the computer networks, makers can refer to rather than a precise description of a real network. In the ISO/OSI model, every node of the network can be sketched as a hierarchical structure of seven levels, as shown in the following diagram:

Functional layers in the ISO/OSI model

The functional layers in the OSI model are explained as follows:

• The first level, starting from the bottom, is level 1, or the physical level. This includes the mechanical and electrical connections between the nodes, together with the software drivers for the communication ports. The features of this level establish some parameters of the network, such as the speed and the transmission...

Supervisory control and data acquisition (SCADA)

SCADA is a software application for the supervision and control of automated processes from a centralized location, both locally and remotely. The heart of a SCADA system is its modular and distributed software architecture. Control systems, which are typically PLCs (but not always), have the responsibility of feeding the SCADA system with the values ​​of the process variables to monitor the machine and the process behavior. The SCADA server nodes have the necessary drivers to communicate with the field devices either through their legacy communication protocols or often through OPC or a fieldbus protocol. At the server level, the data is gathered on a regular basis or, when changes occur, processed to filter noise, and then stored in a real-time database. There are two different types of data collection:

• Polling...

Historian

In the previous sections, we saw how data acquisition in SCADA systems starts from the controllers (the PLCs or the DCSs) or RTUs gathering measurements from sensors and equipment through industrial protocols. The digital representations of these measures are usually called tags or datapoints. Each of these represents a single input or output signal that is monitored or controlled by the system and usually appear as value-timestamp pairs. After generation, the data can also be sent to other monitoring servers for analysis by humans or to the MES system for planning and maintenance. At the same time, data often feeds a specialized database for storing and managing times series. This specialized database is called Historian, or data Historian. Historians are not relational or NoSQL databases; they have fewer capabilities and features and a much simpler structure. However...

ERP and MES

ERP is an information system that integrates all of the relevant business processes of a company, including sales, sourcing, finance, warehouse management, accounting, and so on. This allows the business to manage and keep the whole company under control. If there is an order request, for example, the sales manager can check in real time if a given product is in stock, confirm its availability, and estimate the delivery time. If the order is confirmed, this can be automatically passed to the logistics department, thereby avoiding wasting time and paperwork and bypassing other useless intermediate steps. Nowadays, modern ERP systems cover all areas that can be automated and/or monitored within a company, thus allowing users to operate in a uniform and integrated context, regardless of the application area.

The term MES refers to an information system that has the responsibility...

Summary

In this chapter, we analyzed the main devices involved in the I-IoT data flow in an industrial plant in detail. We started from the generation of the data, looking at how physical measurements are captured by the transducers, converted to a digital signal, and passed through the industrial networks by controllers. We learned that industrial networks provide determinism in message delivery, which is a fundamental requisite in the control process. We discovered the enabling mechanisms that can guarantee deterministic networks. We compared a simplified networking model (an EPA) with the full model of the ISO/OSI stack and we looked at the methods that are used to access the physical link of the control network to ensure that the packet is transmitted within a determined time interval. We also learned that there are different types of industrial networks according to the length...

Questions

1. What is the setpoint in a control chain?
   1. The desired value for a specific process variable
   2. The calculated value for the control variable fitting the reference value
   3. The measurement of the process value coming from the process
2. What is the accuracy in a sensor?
   1. The maximum error that the sensor can make in a measurement operation
   2. The resolution of the sensor
   3. The deterministic error
3. Which is the resolution of a 16-bit DAC converter that has a full-scale voltage of 10 volts?
   1. 0.152 mV
   2. 0.187 mV
   3. 1.5 mV
4. In which electronic device is the A/D are integrated?
   1. Microcontroller
   2. Microprocessor
5. Which are the three PLC graphical languages are provided by the IEC 61131 standard?
   1. Sequential Functional Chart, Ladder Diagram, and Instruction List
   2. Functional Block Diagram, Sequential Functional Chart, and Ladder Diagram
   3. Functional Block Diagram, Sequential Functional...

Further reading

Read the following articles for more information on what we have covered in this chapter:

• Siemens PLC: https://www.siemens.com/global/en/home/products/automation/systems/industrial/controller-magic.html
• Allen-Bradley PLC: https://ab.rockwellautomation.com/Programmable-Controllers
• Omron PLC: https://industrial.omron.co.uk/en/products/programmable-logic-controllers
• ABB DCS: https://new.abb.com/control-systems
• Emerson DCS: https://www.emerson.com/en-us/automation/control-and-safety-systems/distributed-control-systems-dcs
• Siemens DCS: https://www.siemens.com/global/en/home/products/automation/distributed-control-system/simatic-pcs-7/v9.html
• Proficy Historian: https://www.ge.com/digital/products/historian
• Aspen InfoPlus.21: https://www.aspentech.com/en/products/msc/aspen-infoplus21
• Wonderware Historian: https://www.wonderware.com/it-it/industrial-information-management...