Industrial Communication Protocols

Hello Friends

While we are dealing with industries controls and automation, communication is must with high reliability, faster and redundancy for the safe and smooth operation. So for that Industries have given different standard communication protocols based on environment, hardware used and critical level.

So Industries have different communication protocols as below.

1. TCP/IP

2. Profinet

3. Profibus

4. RS 232

5. RS 485

6. Modbus

7. HART

8. AS-I

Here we are discussing about Industrial Automation so based on that we will understand the protocols. First we will see the communication systems Hierarchy. 

 Networking Levels of protocols are also different as per shown below.

1. TCP/IP :-

TCP/IP = Transmission Control Protocol/Internet Protocol is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in the private networks ( intranets)

TCP/IP is a two-layered program

– Transmission Control Protocol - Manages the assembling of a message or file into smaller packets

– Internet Protocol- Handles the address part of each packet so that it gets to the right destination

2. Profinet

PROFINET is the open and innovative standard for industrial automation based on the industrial Ethernet, i.e. you can exchange process data with your machines as before but instead of using a fieldbus system, you use the Ethernet as the medium of communication.

The concept of the PROFINET satisfies all the requirements for industrial automation technology. You can use PROFINET for your factory and process automations that require response time under 100 milliseconds. Other applications, like drive technology applications or clock-synchronized Motion Control, can be served with response time up to less than 1 millisecond. For the purpose of running safety applications, you can use PROFIsafe, which is part of PROFINET. PROFINET technology is developed and published by PROFIBUS/PROFINET International e.V. (PI). It supplements the approved PROFIBUS technology, especially in terms of speed of data transmission and the use of Information Technology (IT). PROFINET uses IT standards such as TCP/IP and XML to communicate, configure and diagnose the machines or field devices.

3. Profibus

PROFIBUS offers functionally graduated communication protocols (Communication Profiles): DP and FMS. Depending on the application, the transmission technologies (Physical Profiles) RS-485, IEC 1158-2 or fiber optics are available. In the course of further technical development, the PROFIBUS User Organization is currently working on the implementation of universal concepts for vertical integration on the basis of TCP/IP. Application Profiles define the options of protocol and transmission technology required in the respective application area for the individual device types. These profiles also define vendor independent device behaviour. 

4. RS-232

The whole purpose of a serial interface is to provide a single path for data transmission wireless or over a cable. Parallel buses are still used in some applications. But with high-speed data so common today, a serial interface is the only practical option for communications over any distance greater than several feet.

Serial interfaces can be used to provide standardised logic levels from transmitters to receivers, define the transmission medium and connectors, and specify timing and data rates. In some cases, they can perform serial-to-parallel and parallel to- serial conversion or specify a basic data protocol.

5. RS-485

The 422 and 485 standards, as they are known today, are balanced data-transmission schemes that offer robust solutions for transmitting data over long distances and noisy environments. These standards don’t specify a logical communication protocol, and are used as the physical layer specification by many protocols such as Modbus, Profibus, DIN-Measurement-Bus and many others.

All Novus products that have serial bus communication follow RS485 standard, due to the advantages it shows in industrial environments. For being so well known all over the world, it is easily accepted. Besides they have been used for a long while, it is still common to find users with some unanswered questions about RS485 and RS422 based networks. Due to this, we propose this document to present a brief explanation on important topics for the design, analysis and installation of a communication networks using the RS485 and RS422 standards.

6. Modbus

MODBUS is a Master/Slave   communications protocol and developed by Gould-Modicon.

The protocol provides for one master device and up to 247 slave devices on a common line. Each device is assigned an address to distinguish it from all other connected device.

Only a master initiates a transaction. (query/response type,  or a broadcast/no-response type.) A transaction comprises a single query and single   response frame or a single broadcast frame.

Fixed characteristic : fixed such as frame format, frame  sequences, handling of communication errors and exception conditions, and the functions    performed.

Characteristic : choice of transmission media, baud rate, character parity, no. of stop bits and the transmission modes.

7. HART

Highway Addressable Remote Transducer

HART is a hybrid communications technology in which a modulated, two-way digital signal is imposed on the industry-standard 4–20 mA analog signal carrying the primary process variable.

The digital signal conveys additional process variables, device status and diagnostics information that can be routed to asset management, process control and safety systems.

This means that HART provides two simultaneous communication channels on the same wire–the industry standard 4–20 mA channel for fast, reliable and robust control (PV) and a digital channel for real-time communication of additional process/device information.

8. AS-I

The AS-I (Actuator Sensor Interface) is matched to the requirements in the lowest level.

AS-I operates actors and sensors with the first control level and replaces them with cable harnesses, distributor cabinets and connecting terminal plates.  Since then, the AS-I is an open standard.  In the meantime, many manufacturers offer intelligent, AS-I compatible actors and sensors in order to be able to transfer more information than only 1/0.

AS-I is especially easy in data manipulation. Field devices are simply clamped into cut terminal technology on an unprotected 2 way conductive flat cable.  As a result, the installation can then be accomplished  by people without any expertise.

AS-I is fast, simple, cost effective and also future safe because it meets more than half of the world market’s requirements for sensors from manufacturers that support it.

PLC Digital Fundamentals

 Dear Readers

As PLC programmer you should have basic knowledge of digital and analog fundamentals for input and output addressing. When we are assigning input or output or memory in PLC logic this addressing concept must need to be clear. So lets start here to understand basic concept.

Bit-Byte Word Concepts

What is a bit?

Bit is short for 'binary digit.' It's a single digit in a binary number, and it can be either 1 or 0.

Inside a computer, you can think of a bit as being a mechanical switch, which can be either switched on or off (the earliest computers actually stored information in memory using mechanical switches, with electromagnets to turn each one on or off).

Now if you only have one of these switches, you can only store two different states, on or off. This is useful in itself, you can record that something is either true or false.

But if you have, say, eight of them, you can store 256 different combinations of on and off states between the eight switches.

What is a byte?

A byte is 8 bits. That's the definition. With 8 bits you can store any number between 0 and 255, since there are 256 different combinations of 1 and 0 to choose from.

Why eight bits? The original intention was that, when storing text, 8 bits would be enough to assign a unique number every possible language character you might want to use in your document. The idea was that each character in a file would take up one byte of memory (in most cases, this is still true).

Let's see: there are 26 uppercase letters (A-Z), 26 lowercase (a-z), 10 numerical digits (0-9), 32 punctuation characters and other symbols on a US keyboard, the space character that’s already 94 different characters. Then there's a few characters for creating newlines, a tab character for indentations, there's even a 'bell' character which programs would output in order to make the user's terminal beep. You can see how it all adds up.

In practice, only characters up to 127 were ever standardized (the standard is called ASCII, which stands for American Standard Code for Information Interchange, because in the early days, one of the eight bits was set aside for error testing purposes (back when computers were far less reliable), and 7 bits only gives you 128 different combinations.

What is a word?

You often hear about 32-bit or 64-bit computer architectures. A word is basically the number of bits a particular computer's CPU can deal with in one go. It varies depending on the computer architecture you're using.

Imagine looking at an imaginary computer's circuitry very closely. On a 32-bit machine, you would see 32 wires running parallel to each other between the computer's memory controller and the CPU, for the purpose of giving the CPU access to one particular word of memory.

Actually, there would be an additional 32 wires (perhaps less) for the CPU to select a particular memory address to access. If a CPU can access 32 bits of memory in one go, then it turns out that it makes a lot of sense to address the computer's memory using ≤32 bits. (This happens to be why the 32-bit version of Windows can't deal with more than 2GB of RAM, but the 64-bit version can.)

What is Variable Frequency Drive ?

Electrical Drive have become the most essential equipment now a days in the electrical motors and other rotating machines. We know that electrical drives mainly accomplish three kinds of work, Starting, Speed control & Braking.

 It can be said that the electrical drives enable us to control the motor in every aspect. But control of electrical drives is also necessary because all the functions accomplished by the drives are mainly transient operations i.e. the change in terminal voltage, current, etc are huge which may damage the motor temporarily or permanently. That’s why the need of controlling the drives rises and there are various methods and equipment's to control different parameters of the drives. In very simple words, the systems which control the motion of the electrical machines are known as electrical drives.

A typical drive system is assembled with an electric motor (may be several) and a sophisticated control system that controls the rotation of the motor shaft. Now a day, this control can be done easily with the help of software. So, the controlling becomes more and more accurate and this concept of drive also provides the ease of use.

There are many types of VFD which are based on motors types.

1. AC Drives for AC motors like Induction Motor

2. Stepper Drives

3. Servo Drives

4. DC Drives for DC motors

What is Mechatronics ?

Mechatronics is combination of some engineering fields like mechanical engineering, electrical engineering, instrumentation & control engineering, electronics engineering etc. Originally, mechatronics just included the combination of mechanics and electronics, hence the word is a combination of mechanics and electronics; however, as technical systems have become more and more complex the word has been broadened to include more technical areas.

Mechatronics is a field of study that focuses on the integration of mechanical, electrical, fluid, and computer technologies to control machine movements. Introduced in the early 1970’s by a Japanese firm describes the advent of mechanical equipment (mecha) that uses electronics (tronics) for decision making functions decision making function most often performed by a computer.

Why choose mechatronics?

Mechatronics is not a subject, science, or technology. It is a fundamental way of looking at and doing things. Now a days mechatronics is everywhere in process industries. Every machine is having mechanical setup with some intelligence. To better understand any machine which is having intelligence we should have knowledge of all like mechanical setup, sensors & actuators, electrical component & connections, controller etc. And getting knowledge all of it, is mechatronics. So knowledge of mechatronics is very much important because we are surrounded of mechatronics systems. In industry demand for mechatronics engineer is increasing. Person who knows mechatronics can work in process industries very efficiently.

Where can I work as a mechatronics engineer?

Mechatronics professionals are the technicians and engineers who design and maintain automated equipment. Technicians and engineers conduct their work in laboratories, offices or on-site at manufacturing plants. These professionals work toward the same goal of producing safe and efficient automated equipment. While technicians primarily maintain machinery, engineers are more concerned with the design and development of components and products.

Mechatronics technicians apply their knowledge of engineering to solve technical problems and maintain automated mechanical equipment. This may entail inspecting, troubleshooting and repairing electrical and electronic components. They work beside engineers and scientists, often assisting in the research and development of production. Technicians, as well as engineers, are needed in a variety of industries, including manufacturing, construction, agriculture, aerospace etc.

How I learn mechatronics system?

Mechatronics training programs for beginners are available at the undergraduate level. Those interested in taking their studies to the next level can find master's degree programs in this field.

Students will receive instruction about a combination of electronic, mechanical, computer and control engineering. Many degree programs offer students the chance to engage in practical experience through laboratory work and internship opportunities with local corporations.

Benefits

1. Enhanced features and functionality

2. More user-friendly

3. Precision control

4. More efficient

5. Lower cost

6. Flexible design (reprogrammable)

7. More reliable

8. Smaller

9. Safer

For more details to learn about PLC SCADA HMI PI DCS and Industrial Automation Please watch youtube channel " "Automation Revolution"

What is Process Instrumentation?

Instrumentation is the variety of measuring instruments to monitor and control a process. It is the art and science of measurement and control of process variables within a production, laboratory, or manufacturing area. An instrument is a device that measures a physical quantity such as flow, temperature, level, distance, angle, or pressure. Instruments may be as simple as direct reading thermometers or may be complex multi-variable process analyzers. 

Instruments are often part of a control system in refineries, factories, and vehicles. The control of processes is one of the main branches of applied instrumentation. Instrumentation can also refer to handheld devices that measure some desired variable. Diverse handheld instrumentation is common in laboratories, but can be found in the household as well. For example, a smoke detector is a common instrument found in most western homes.

Instruments attached to a control system may provide signals used to operate solenoids, valves, regulators, circuit breakers, or relays. These devices control a desired output variable, and provide either remote or automated control capabilities. These are often referred to as final control elements when controlled remotely or by a control system. A transmitter is a device that produces an output signal, often in the form of a 4 20 mA electrical current signal, although many other options using voltage, frequency, pressure, or Ethernet are possible.

This signal can be used for informational purposes, or it can be sent to a PLC, DCS, SCADA system, Lab VIEW or other type of computerized controller, where it can be interpreted into readable values and used to control other devices and processes in the system. Control instrumentation plays a significant role in both gathering information from the field and changing the field parameters, and as such are a key part of control loops.

Importance of process parameters: 

 Process Parameters (also called a process variable) are certain measures that refer to status of the process (their values indicate whether the process meets the plan or it needs adjustment). In order to obtain effective execution of the process its parameters should stay under continuous control.

The simplest examples of parameters you can find in a manufacturing process are pressure, temperature, and chemical composition – anyone of these may have its desired value that is called a set-point that regulates proper functioning of process elements and operations, while if a parameter deviates from its set-point (goes beyond the acceptable level of variance), then probably a process tends to fail, hence special automatics or human operators should intrude into this process to adjust it and prevent upset.

The Process Variables used in instrumentation are:

 Flow - Defined as volume per unit of time at specified temperature and pressure conditions, is generally measured by positive-displacement or rate meters. Units: kg / hr., litter / min, gallon / min, m3 / hr., Nm3 / hr. (gases)

 Pressure - Force acting per unit Area. P = F/A. Units: bar, Pascal, kg / cm2, lb. / in2.

 Temperature - It is the degree of hotness or coldness of a body. Units: Degree Centigrade, Degree Fahrenheit, Degree Kelvin, Degree Rankin.

 Level - Different between two heights. Units: Meters, mm, cm, percentage.

What is Process Control ?

Process control is extensively used in industry and enables mass production of consistent products from continuously operated processes such as oil refining, paper manufacturing, chemicals, power plants and many others. Process control enables automation, by which a small staff of operating personnel can operate a complex process from a central control room.

In reality, the controller is just a partner. A process will respond to a controller’s commands only in the manner which it can. To understand process control you must understand the other partners as well: sensors, final control elements and the process itself. All of these determine what type of response the controller is capable of extracting out of the process. 

It is not the other way around Process control is an engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of Specific process within a desired range. For instance, the temperature of a chemical reactor may be controlled to maintain a consistent product output. Process control is extensively used in industry and enables mass production of consistent products from continuously operated processes such as oil refining, paper manufacturing, chemicals, power plants and many others. Process control enables automation, by which a small staff of operating personnel can operate a complex process from a central control room.

Components of Process Control

A controller seeks to maintain the measured process variable (PV) at set point (SP) in spite of unmeasured disturbances (D). The major components of a control system include a sensor, a controller and a final control element. To design and implement a controller, we must:

 Have identified a process variable we seek to regulate, be able to measure it(or something directly related to it) with a sensor, and be able to transmit that measurement as an electrical signal back to our controller, and

 Have a final control element (FCE) that can receive the controller output (CO) signal, react in some fashion to impact the process (e.g., a valve moves), and as a result cause the process variable to respond in a consistent and predictable fashion.

What is SCADA ?

What is SCADA ?

SCADA is an acronym for Supervisory Control and Data Acquisition. SCADA systems are used to monitor and control a plant or equipment in industries such as telecommunications, water and waste control, energy, oil and gas refining and transportation. These systems encompass the transfer of data between a SCADA central host computer and a number of Remote Terminal Units (RTU) and/or Programmable Logic Controllers (PLCs), and the central host and the operator terminals.

A SCADA system gathers information (such as where a leak on a pipeline has occurred),transfers the information back to a central site, then alerts the home station that a leak has occurred, carrying out necessary analysis and control, such as determining if the leak is critical, and displaying the information in a logical and organized fashion. These systems can be relatively simple, such as one that monitors environmental conditions of a small office building, or very complex, such as a system that monitors all the activity in a nuclear power plant or the activity of a municipal water system. Traditionally, SCADA systems have made use of the Public Switched Network (PSN) for monitoring purposes. Today many systems are monitored using the infrastructure of the corporate Local Area Network (LAN)/Wide Area Network(WAN). Wireless technologies are now being widely deployed for purposes of monitoring.

SCADA systems consist of

 One or more field data interface devices, usually RTU, or PLCs, which interface to field

sensing devices and local control switchboxes and valve actuators

 A communications system used to transfer data between field data interface devices and control units and the computers in the SCADA central host. The system can be radio, telephone, cable, satellite, etc., or any combination of these.

 A central host computer server or servers (sometimes called a SCADA Centre, master station, or Master Terminal Unit (MTU)

 A collection of standard and/or custom software [sometimes called Human Machine Interface (HMI) software or Man Machine Interface (MMI) software] systems used to provide the SCADA central host and operator terminal application, support the communications system, and monitor and control remotely located field data interface devices. 

SCADA functions

A supervisory control and data acquisition (SCADA) system performs the following major functions:

1. Human-machine interface (HMI)

2. Electrical communication

3. Data acquisition (DAQ)

4. Monitoring

5. Control

6. Data collection, storage and retrieval

7. Calculation

8. Report generation

PLC Architectures

In this topic we will learn what is the architecture and functional block diagram of PLC ?

Every PLC has three types of main modules.

1. Input Module

2. Output Module

3. CPU or Processor

So lets discuss about all these modules in details.

1. Input Module

Input modules in PLC are two type . 1. Digital Input and 2. Analog Inout

So digital Inputs are like ON -OFF switches , Proximity sensors, Toggle Switches , Push buttons or any digital types of inputs. 

In Analog input Pressure, Temperature, Flow, Humidity, Level different type of physical quantity measurement sensors with transmitters in standard analog input 4 to 20 ma or +_10 V.

2. Output module 

Same as Input , outputs are also two types Digital and Analog.

In Digital output Solenoid valves, Lights, Indicator, Hooter and analog output would be I to P converter, Variable Frequency Drive, Proportional Valve.

3. CPU or Processor 

CPU is the brain of this PLC , All logic are written in memory of the CPU and there are various part of the CPU as show in Diagram. CPU will execute the logic written in memory accordingly Signal received from input and update output.

Scan cycle of PLC

A PLC program is generally executed repeatedly as long as the controlled system is running. The status of physical input points is copied to an area of memory accessible to the processor, sometimes called the "I/O Image Table". The program is then run from its first instruction rung down to the last rung. It takes some time for the processor of the PLC to evaluate all the rungs and update the I/O image table with the status of outputs. This scan time may be a few milliseconds for a small program or on a fast processor, but older PLCs running very large programs could take much longer (say, up to 100 ms) to execute the program. If the scan time were too long, the response of the PLC to process conditions would be too slow to be useful.

Special-purpose I/O modules may be used where the scan time of the PLC is too long to allow predictable performance. Precision timing modules, or counter modules for use with shaft encoders, are used where the scan time would be too long to reliably count pulses or detect the sense of rotation of an encoder. The relatively slow PLC can still interpret the counted values to control a machine, but the accumulation of pulses is done by a dedicated module that is unaffected by the speed of the program execution

What is PLC ?

A programmable logic controller (PLC) is an industrially hardened computer-based unit that performs discrete or continuous control functions in a variety of processing plant and factory environments. Originally intended as relay replacement equipment for the automotive industry, the PLC is now used in virtually every industry imaginable. Though they were commonly referred to as PCs before 1980, PLC became the accepted abbreviation for programmable logic controllers, as the term “PC” became synonymous with personal computers in recent decades

Difference between PC & PLC

The PC is designed to be flexible and handle thousands of different types of applications, but PLCs are especially designed for control.35 PCs started showing up on the factory floor in the mid-80s in programming and HMI applications. However, now the PC is migrating toward actual control. In response, PLC manufacturers have adapted PC technology, such as Ethernet. Some systems actually provide a “PC on a card” to plug into the PLC back plane.11 PLCs are often thought of as computers. To a certain extent this is true; however, there are important differences between PLCs and computers.

Real-Time Operation/Orientation the PLC is designed to operate in a real-time control environment. The first priority of the CPU is to scan the I/O for status, make sequential control decisions (as defined by the program), implement those decisions, and repeat this procedure all within the allotted scan time. Most PLCs have internal clocks and “watchdog timers” built into their operations to ensure that a software error like “divide by zero” or an endless loop does not send the central processor into an undefined state. When the watchdog time is exceeded, the processor shuts down in a predetermined manner and usually turns off all outputs. In real time systems, reliability is a big concern. PLC manufacturers’ experience shows mean time between failures (MTBF) ranging from 20,000 to 400,000 hours. “This is far in excess of almost any other type of electronic or control equipment.”

Environmental Considerations PLCs are designed to operate near the equipment they control. This means they function in hot, humid, dirty, noisy, and dusty industrial environments. Typical PLCs can operate in temperatures as high as 140F (60C) and as low as 32º F (0C), with tolerable relative humidity ranging from 0 to 95% noncondensing. In addition, they have electrical noise immunities comparable with those required in military specifications.

Programming Languages and Techniques PLC languages are designed to emulate the popular relay ladder diagram format. This format is read and understood worldwide by maintenance technicians as well as engineers. Unlike computer programming, PLC programming does not require extensive special training. Applications know-how is much more important. Although certain special techniques are important for programming efficiency, they are easily learned. The major goal is the control program performance. Another difference between computers and PLCs is the sequential operation of the PLC. Program operations are performed by the PLC in the order they were programmed (Figure 5.4o). This is an extremely useful feature that allows easy programming of shift registers, ring counters, drum timers, and other useful indexing techniques for real-time control applications.

Advantages & Disadvantages of PLC

Advantages:

 Very High Accuracy

 Low Power Consumption (Energy Saving)

 High Level human Safety

 Less Plan Running cost

 Small in Size (Required Lased space)

 Rugged Construction

 Easily programmable

 Easy Maintenance

 Economical & high Flexible

 Shorter project program

 Easy Documentation

Disadvantages:

 High Skilled Engineering Required for that high skilled person required

 Difficulty with changes or replacements

 Some high Initial Cost.

There are many PLC make companies like SIEMENS, ABB, MItshubishi, GE, Omron, Delta,Honeywell. They have their own software for the PLC programming.

What is Industrial Automation ?

The word ‘Automation’ is derived from Greek words “Auto” (self) and “Matos” (moving). Automation therefore is the mechanism for systems that “move by itself”.

However, apart from this original sense of the word, automated systems also achieve significantly superior performance than what is possible with manual systems, in terms of power, precision and speed of operation.

Definition: Automation is a set of technologies that results in operation of machines and systems without significant human intervention and achieves performance superior to manual operation

A Definition from Encyclopedia Britannica: The application of machines to tasks once performed by human beings or, increasingly, to tasks that would otherwise be impossible.

Although the term mechanization is often used to refer to the simple replacement of human labor by machines, automation generally implies the integration of machines into a self-governing system.

Types of automation

Automation systems can be categorized based on the flexibility and level of integration in manufacturing process operations. Various automation systems can be classified as follows

Fixed Automation: 

It is used in high volume production with dedicated equipment, which has a fixed set of operation and designed to be efficient for this set. Continuous flow and Discrete Mass Production systems use this automation. E.g. Distillation Process, Conveyors, Paint Shops, Transfer lines etc. A process using mechanized machinery to perform fixed and repetitive operations in order to produce a high volume of similar parts.

Programmable Automation: 

It is used for a changeable sequence of operation and configuration of the machines using electronic controls. However, non-trivial programming effort may be needed to reprogram the machine or sequence of operations. Investment on programmable equipment is less, as production process is not changed frequently. It is typically used in Batch process where job variety is low and product volume is medium to high, and sometimes in mass production also. E.g. in Steel Rolling Mills, Paper Mills etc.

Flexible Automation: 

It is used in Flexible Manufacturing Systems (FMS) which is invariably computer controlled. Human operators give high-level commands in the form of codes entered into computer identifying product and its location in the sequence and the lower level changes are done automatically. Each production machine receives settings/instructions from computer. These automatically loads/unloads required tools and carries out their processing instructions. After processing, products are automatically transferred to next machine. It is typically used in job shops and batch processes where product varieties are high and job volumes are medium to low. Such systems typically use Multipurpose CNC machines, Automated Guided Vehicles (AGV) etc.

Integrated Automation: 

It denotes complete automation of a manufacturing plant, with all processes functioning under computer control and under coordination through digital information processing. It includes technologies such as computer-aided design and manufacturing, computer-aided process planning, computer numerical control machine tools, flexible machining systems, automated storage and retrieval systems, automated material handling systems such as robots and automated cranes and conveyors, computerized scheduling and production control. It may also integrate a business system through a common database. In other words, it symbolizes full integration of process and management operations using information and communication technologies. Typical examples of such technologies are seen in Advanced Process Automation Systems and Computer Integrated Manufacturing (CIM).

For more details to learn about PLC SCADA HMI PI DCS and Industrial Automation Please watch youtube channel " "Automation Revolution"