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The Difference Between Profibus And Profinet

Profibus and Profinet are two terms that are often confused with each other, both of them being field networks part of industrial automation protocols. However, there are significant differences between the two in various aspects and for the same reason are used for different purposes in industries.

In order to clearly understand their functioning and application of the two, it is important to first get a good grasp of the basics.

The basics

Profibus which is the acronym for Process Field Bus is basically a standard for fieldbus communication used in automation technology. Profinet on the other hand, which is acronym for Process Field Net is a standard for internet communication over industrial Ethernet.
As they are both very popular and highly sought after automation protocols created by the same organization, they do share a number of similarities. They are both created and maintained by Profibus and Profinet International.
However, Profinet comparatively has extra advanced capabilities that facilitate a faster and a more flexible field of communication within a network.

ethernet_profinet_graphicThey share the same application profiles; which essentially implies that they have similar guidelines followed by different categories of devices within a network, regarding their use of Profibus and Profinet data during communication. These profiles enable smooth planning and functioning of the automation systems and devices.

Other than that they are also very similar in terms of their engineering concepts and they use General Station Description files to define the hardware for each device. The file type however is different.

In simple terms Profibus is a classic and traditional automation protocol based on serial communication while Profinet is a newer enhanced automation protocol based on Industrial Ethernet.

Significant points of differences

Profibus and Profinet use GSD files for define the hardware for various devices. But as mentioned before, the difference lies in the type of file being used. Profibus uses ASCII files whereas Profinet uses XML files.

In terms of their base field, Profinet made the move from RS-485 to Ethernet to become more efficient and ubiquitous. It is a more adaptable and modern technology that helps organizations future-proof their processes.
Besides that, being based on industrial Ethernet, Profinet also enjoys a higher bandwidth, a larger size of message and unlimited amounts of address space. Separate controllers attached to the network may have to adhere to certain limitations in terms of address space, depending on their memory capacity and processor capabilities though.


Other than that, Profinet is faster than Profibus because of the provider/consumer model that it uses, where any node in the network is allowed to communicate at any given time. Hence, there is no delay in information exchange.
Besides that, Ethernet networks are generally switched networks that are practically devoid of network collisions.
Profibus uses a master/slave approach rather than a provider/ consumer model where the master is usually in charge of the entire network and the nodes are allowed to communicate only when prompted.

Usually industrial enterprises are required to deploy separate gateways in order to communicate with other networks. However, with Profinet, it creates its own proxies for translation and data exchange between two different networks and unlike an ordinary gateway they are defined in an open standard.
In case of Profibus, there is a facility for wireless transmission of messages; however, it requires similar based proprietary radios at both ends.
As Profinet works on standard Ethernet, it can easily use WiFi or Bluetooth for wireless transmission.

Even though Profinet is an enhanced and more versatile version of Profibus, it does not mean that the former can be used across industries regardless of the processes. It is important to study the field of automation and choose the protocol accordingly.

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RSLinx: Essentials to Know

rslinx1Communication software has come a long way from basic emails and chat systems now. Advanced technologies these days provide more than just a mechanism for different systems and users to exchange files and terminal emulators among themselves.

As devices are getting smarter by the day, there is indeed a need for more intelligent mediums facilitating communication between the same.

RSLinx is one such communication software developed by Rockwell Automation.

What is RSLinx?

RSLinx is basically a windows-based communication software or server often used to interface and facilitate seamless communication among all of the Rockwell industrial control and automation hardware. The RSLinx Classic, which is one of the most popular versions of RSLinx, also provides plant-floor device connectivity in automation industries for a wide range of Rockwell software applications like RSView 32, Factory Talk View Site Edition and Factory Talk Transaction Manager as well.

It comes in a variety of types with minor variations in terms of their capabilities, inclusions and in turn their usability. Some of them are:

  • RSLinx-OEM – this provides DDE capability meant for Rockwell DDE enabled software.
  • RSLinx Professional – this again provides DDE capability to DDE enabled software
  • RSLinx Lite – this acts as a PLC programming software communication interface
  • RSLinx SDK – this is a complete Software Development Kit that includes the OEM version as well.

RSLinx makes use of OPC or DDE to provide connectivity for client applications, although OPC is the preferred and more commonly used interface for data acquisition applications as it is considered as a factory standard for communications.

RSLinx comes with a number of major benefits including a very user-friendly graphical interface, multiple data value viewing options and ladder viewers to facilitate viewing ladder codes. It can thus be used to communicate from anywhere to anywhere.

What is RSLogix?

RSLogix; an RSLogix client, is the programming software for which RSLinx facilitates communication. It is a design and configuration software developed based on the Rockwell Automation Integrated Architecture. It supports a wide range of applications from discrete to process to motion to safety to batch and drive based applications.

It serves as a single control platform for any kind of automation discipline in industries as it provides a common engine and development environment. It features unique capabilities like ladder logic, structured text, sequential function chart editors and function block diagrams. It also comes with troubleshooting tools1 and advanced diagnostics.

Apart from that it also has an easy-to-use IEC 61131-3 compliant interface along with a holistic instruction set that caters to a wide array of applications. Put together with the Integrated Architecture System it helps industries to enjoy plant-wide optimization of processes in an efficient and effective manner.

What is RSLinx Gateway?

The RSLinx Gateway basically helps extend the communication network throughout an organization. It enables RSLinx clients such as the RSLogix 5000 or RSLogix 500 to go online and connect with processors like the PLC-5, SLC-5, MicroLogic or ControlLogix residing on a particular control network over the Ethernet.

RSLinx Gateway is also used to optimize communication between various OPC clients and other devices on the same floor in industries. It facilitates hassle-free communication by consolidating multiple data requests from different clients, into one single request which is forwarded to the controller. This essentially helps in reducing the overall network traffic and data load on the end controller.

This is beneficial in terms of cost-reduction as well, as it eliminates the need for an RSLinx copy to be kept active on each client machine.

How do I download RSLinx?

Owing to recent design changes on the Rockwell Automation website, the free version of RSLinx is a little difficult to find. The direct link to the download used to be available on the first page of results when you searched for “micrologix downloads” on the main page of Rockwell Automation. But it is not available anymore.

However, the link still is available on the website. All you have to do is go to the product compatibility and download centre.

–          From there click on “find downloads” and type in “RSLinx” in the search column.

–          From the list of options that show up click on RSLinx Classic Lite (free version).

–          Once you’re taken to the product page, click on the download button.

From there, all you have to do is follow instructions. If you are a first time visitor to the Rockwell Automation website or if you’re using their software for the first time, you might need to create a work-based account first.

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Everything You Need To Know About Ethernet Network Communication

ieb44tunnel1In terms of computing and networking, the Ethernet or the Local Area Network (LAN), MAN and WAN of computer systems that we use for commercial purposes or otherwise has a rich set of protocols and formatting regulations that enable a smooth network connection. It is responsible for the clear and smooth transmission of data across network devices as well as over the network connection.

In order for the Ethernet to control, monitor and regulate data being transmitted across networks, it makes use of specific technology and features including an Ethernet gateway. Let’s learn more about how the Ethernet facilitates communication across networks.

What is an Ethernet gateway?

An Ethernet gateway, sometimes called a router is basically a node or one of the communication endpoints in a computer network that uses the Internet Protocol Suite that is responsible for forwarding data packets to other networks in cases where the network protocols are similar.

In other words, a default gateway serves as a router or a forwarding host to redirect data packets, while also being a common access point to other networks. This may involve not just address changes but also completely different networking technologies with different network prefixes as well. Such gateways are called internet gateways.

Now both the internet gateway and the router or the Ethernet gateway, are nodes that connect and regulate traffic between two or more networks. But the type of networks being handled is what is different.

A Windows 2000 network that uses the TCP/IP internet protocol as its primary protocol can use a router or an Ethernet gateway to connect to the internet as it is the same primary protocol that the internet uses.

An internet gateway on the other hand would be used to connect a Windows NT network for example with a NetWare network.

How does the Ethernet gateway work?

The Ethernet gateway is always connected to two or more different data lines from different networks. It reads the destination IP addresses on data packets coming in from the data lines and determines the ultimate destination. Then it makes use of the information on its routing table or the Routing Information Base (RIB) and directs the data packet to the next network on its route or journey. RIB is basically a data table that has a list of routes to particular destination addresses and sometime even the distance information associated with these routes.

The Ethernet also makes use of Ethernet converters and serial to Ethernet converters for converting media and data signals.

What is an Ethernet converter?

An Ethernet converter also called an Ethernet media converter is basically a device that is designed to enable the communication and smooth connection between different networking media such as fibre and co-axial cables used by different networks. It usually comes in the form of a small box and typically it is used to connect fibre media coming from an optical fibre based network and a copper-based network which is more conventional.

What is a serial to Ethernet converter?

Just like the media used by different networks, the data signals across networks may also come in serial form, which need to be converted to Ethernet packets in order to be routed and processed. This job is done by serial to Ethernet converters which are also called terminal servers or device servers as they are devices that have their own IP address.

It basically is a device that converts serial RS232, RS485 or RS422 data to Ethernet packets and also Ethernet TCP/IP packets back to these serial data signals. It comes in different models that facilitate different conversions.

How does a serial to Ethernet converter work?

A serial to Ethernet converter device usually comes with driver software that you need to install on your PC. The program creates virtual COM ports within the system when the converter is connected to the system. You can see all the virtual ports created by the software on your device manager list.

When you connect a serial device to one of the hardware ports on your converter device, the peripheral gets redirected to the visual serial port of your system and is identified by your PC as a local device. The circuitry within the converter then goes about converting each of the signals to Ethernet data packets for effective communication.

Difference Between Allen Bradley And Siemens PLC

One of the biggest boons that the industrial sector of the world at large received came in the last century. We are talking about the invention of the Programmable Logic Controller (PLC) by Dick Morely back in 1969.

Ever since then, there have been many innovations in terms of functionality and hardware features for the control system and needless to say, each new one has been tough to beat. There are predominantly two giants who have had the duopoly in the manufacture of efficient PLCs for a long time now and they are Siemens and Allen Bradley.  


While each of these are established and top notch companies who have already proved the worth of their super-efficient TLCs individually, there has forever been a debate over which of these is better.

So here is a detailed comparison between the Allen Bradley and Siemens PLCs.

Before we begin, a quick word about what a PLC is.

What is a PLC?

In the simplest of terms, a Programmable Logic Controller or PLC is an industrial computer control system that allows you to get the most out of industrial processes. It helps enhance the processes while at the same time allowing you to switch up, replicate or change the processes as well quite easily.

Allen Bradley Vs. Siemens PLC

First things first, the quality and functionality of the hardware are significantly distinct. Both the AB and the Siemens PLCs work pretty much the same way and are equally reliable. The difference lies in their installation processes.

While the Allen Bradley requires you to connect the PLC to both the Allen Bradley power supply as well as the Allen Bradley rack, the Siemens one works with pretty much any 24 V DC supply of power. Also, you might need to install additional safety communication ports for Rockwell while Siemens already comes with built-in communication ports.

Another major difference is in the protocols they use. AB uses mostly native American IPs such as DeviceNet, ControlNet and EthernetIP, and also the DH+ or DH485.

At the same time, Siemens uses European native IPs such as Profibus and ASI and also serial MODBUS or MODBUS TCP/IP.

image3Coming to the interface and ease of use, AB has a more intuitive and easier user interface and it allows users to manage and control their processes even without a lot of programming knowledge. It also has excellent features like communicative abilities with third party hardware, mass production of code and even export and import of tags from Excel to scada databases.

Siemens might be a little complex for the maintenance staff that may not have a programming background.

On the flip side, Siemens offers a lot of options to program and customise the process to suit your business model.


As for the pricing aspects, Allen Bradley definitely is more expensive when compared to the Siemens PLC. However, Siemens offers standard technical support at all times at no additional costs while AB does charge you for technical support according to the amount of hardware you have installed.

That said, it would be ideal to choose one of these according to your priorities in terms of business processes.

Now if you have both Allen Bradley and Siemens devices and you want them to communicate, then you can use Equustek DL3500-MODBUS/DH+ or DL3500-MODBUS/DH485 for All Siemens that can handle uses serial MODBUS and Allen Bradley that support DH+ or DH485, or use the DL6000-MEDH+ or DL6000-MEDH485 that allow Siemens with MODBUS TCP/IP to communicate with Allen Bradley DH+ or DH485 devices.

Modbus And RS485: Everything You Need To Know

In the world of industrial internet communication and networking, there are a lot of minute details that contribute towards giving us the convenience of information at our fingertips. From the type of computer network at the client end to the internet protocol to the databases being used, there are a lot of things that must come together in order to make a simple search request or process automation successful.

One such detail that plays a very important role in making exchange of information smooth and successful is the Modbus protocol along with the RS485.

These are two different but related concepts that people are often confused with. So let’s see what they are in detail.

What is Modbus and Modbus RS485?

Simply put, Modbus is basically a protocol that facilitates communication between the “master” or the host and the “slaves” or the connected devices. It enables the host to read the measures and aids in the configuration of devices.

On a basic level, the Modbus protocol facilitates communication with the help of messages that equate to simple operations necessary to read and write regular 16 bit words and binary details or registers called “coils”. The host or the master usually initiates the exchange and the slave or the device usually replies.

Hence, as is evident, the Modbus protocol literally defines the messaging structure used in the exchange of data between the host and the slaves or the devices.

It must not be confused with a medium of communication though. It forms the messaging structure alone and is not the physical medium of data exchange.

Now, in a normal stream of industrial data exchange or communication during process automation, there usually is a master which most often is a Building Automation System or a BAS, a communications gateway device, and a PLC or a software program that is running on a computer.

In order for the data exchange to happen, the host requires a medium that not only facilitates the exchange but also determines the pace.

Enter RS485.

It is basically an electrical or serial transmission standard that defines the physical level of electrical signals between the host and the slaves and also the wiring that enables the transfer of data. It is a popular standard used in data exchange as it allows the usage of several devices using the same standard on the same bus, which eliminates the need to multiply interfaces on the host while querying multiple devices.

Hence, when we say Modbus RS485, it denotes the protocol being used in process automation along with its ability to communicate effectively by the name of serial transmission standard.

On a normal case, a single multi-drop RS485 serial bus can facilitate up to 127 slave devices, which again is a good reason for its popularity.

Is Modbus the same as RS485?

The answer is no, because both of these are relative concepts that need each other in order to fulfil their purposes. Modbus defines the protocol type and RS485 defines the signal level on the protocol.

PLC 101: Functioning And Deployment

A PLC which stands for Programmable Logic Controller, is basically a technology used to control automated systems in various industries. It is an important part of process automation across industries these days and they constitute simple forms of control systems that have been increasingly replacing hard wired logical relays spread out on a large scale of late.

It is similar to typical PCs in certain hardware and terminologies such as central processing units, memory and communication. However a PLC is designed to operate in more rough and rugged industrial surroundings and is also more flexible in terms of interfacing with inputs fed in as well as outputs generated.

How a PLC works

The working or functioning of a PLC is dependent on its 3 main components. As mentioned before, just like how a normal PC has a CPU, a PLC also has similar parts that decide how it functions. They are:

–          The Central Processing Unit (CPU)

–          The power supply and rack

–          The input and output section

An additional segment can be identified for a PLC considering its industry-heavy application and that is the program section.

In brief terms, PLCs work as per the following sequence:

  • The input section first converts real time analogous electric signals that it receives into digital electric signals which the PLC uses with the help of certain connector rails
  • The CPU then stores these digital electric signals in the PLC external memory space. The locations are called bits.
  • In the next step, the programmable instructions are spelled out for the device in the form of mnemonics and symbols which are then stored in the user memory.
  • Then, just like in a typical PC, the CPU extracts these programmable instructions and executes them by manipulating and processing the inputs so as to control the output devices.
  • The results of the implementation get stored in the external memory space that controls the output devices

In addition to these, the CPU also performs the functions of updating input storage with changes attributable to the alterations in output content. At the same time it also performs internal functions like resetting the timer and keeping a check on the user memory.

What is PLC control?

PLC control is nothing but the control affected through the deployment of PLC automation software. From a general perspective, a PLC helps control different devices working in an industry without being too rigid with the process flow. For the same reason, it is often known as a method of “softwiring” the different devices involved in process automation.

They are known to provide this kind of flexibility without compromising on reliability and robustness. They eliminate program crashes or other mechanical level failures as well.

Moreover, as they are available in even small sizes, they are more compact and much more economical when compared to traditional control systems.

What is PLC training?

PLC training refers to the employee level skill development and training imparted in order to familiarize the concept and functioning of a PLC in any industry. As is the case with any new deployment in any industry or office, new process automation software deployment also requires the management to carry out specific training programs for the middle and lower level employees, who may be operating the system.

Additionally, PLC being an industry norm these days, there are also specialized PLC technician training programs offering professional qualification with valid certification for prospective PLC operators who may be interested in pursuing a career in the same. The program typically involves modules detailed on the basic knowledge and skills required to work with a PLC system within an industry.


Difference between RS485 and Profibus

When it comes to industrial networking, there are many specifications that govern the smooth exchange of information across hosts, slaves and throughout the network. All of these may be familiar with people who have mastered the art of network communication, but anyone who is starting out could be easily confused between the technical terms and accessories.

One such commonly confused pair of technical terms is the RS485 and Profibus.

Now people who do have a fair idea about the whole data exchange system in industrial networking would know that these are two very important contributors for smooth process automation. But, from a more detailed perspective, these are two different aspects related to the same concept.

Let’s get in to what each of these is.


Profibus stands for Process Field Bus. It is basically a standard of fieldbus communication used in automation technology. And field bus refers to the network protocols used for real-time distributed control.

There are two versions of the standard being used in industries. One of them is Profibus DP which stands for Decentralised Peripherals and the other is Profibus PA which stands for Process Automation. Out of these the Profibus DP is more commonly used by industries while the Profibus PA is more application specific and is hence lesser used.

Profibus DP is meant to be used to control and operate sensors and actuators through a centralized platform for automation applications in production industries and factories. It includes diagnostic options as well.

Profibus PA on the other hand is mainly used to monitor measuring equipment through a process control system of course. It is specifically meant to be used in explosion prone or hazardous areas.


The RS485 is also a standard, but it defines the electrical signal levels in the communication between drivers and receivers or hosts and slaves in networking. In this case though, the electrical signalling is more balanced and multi point systems are also supported. For the same reason, the RS485 is a very useful and popular standard in industrial control systems. It is more so as it is capable of being connected with multiple receivers, whether in a linear or a multi drop bus and it supports both Local Area Networks as well as multi drop communication links and works with data rates up to 10 Mbits.

Difference between Profibus and RS485

Both the Profibus and the RS485 are standards used in communication during process automation. However, they are used in different aspects of communication.

Profibus is a very flexible and reliable communication technology where issues can be caused by small and simple errors. On the other hand, RS485 is a more balanced technology that makes use of a two-wire transmission system. In effect this makes it the difference in voltage between the two wires among which the communication or data exchange is happening. For the same reason that it doesn’t depend on the voltage directed to the ground, it is more stable. This also makes it less sensitive to interference when compared to a single-ended transmission.

Industrial Automation And PLC Programming; The Basics

In the field of industrial automation, we have been seeing and experiencing technologies that have made the process one step easier with each development. From the simplest computing devices initially developed to replace hardwired relays throughout industrial manufacturing processes, to complex systems that enable manufacturers to generate performance reports, industrial automation has come a long way and manufacturing units have been competing for the cutting edge with these advancements.

On the subject of advancements, two particular technologies that majorly revolutionized the concept of automation were PLCs and microcontrollers. Being on the same line of use, the two are quite often confused with each other and sometimes even understood as the same due to technical similarities.

Here is some insight into the major differences between them.

What is the difference between PLC and microcontroller?

To put things in to perspective, a PLC or a Programmable Logic Controller is basically a specifically designed computing device used in industry automation. They can be said to be one of the first and minor advancements in the field, as their initial purpose as mentioned before, was just to replace hardwired relays or timers or other sequences used in the industry. Now there are much more advanced versions of PLCs designed to be scalable and dynamic, compatible even with lines based on robotics. For the same reasons, they are the most commonly adopted computing system across industries. They are also known for their ability to work seamlessly in rough or rugged industrial environments, not to mention their real time responses that save time.

image1Microcontrollers on the other hand are much smaller computing devices when compared to PLCs. They essentially work on a single chip and they may contain one or more processing cores along with memory devices. The similarity with PLCs is that they too are used in almost all devices that play a role in daily activities, but the difference is that microcontrollers are specifically used in applications where only certain repetitive tasks are required to be performed. Additionally, they are also mostly bare and do not possess interface elements like display or switches like PLCs.

Suffice it to say PLCs are generally considered better equipped for advanced and complex industrial environments.

What are the three types of PLC?

There are 3 types of PLCs that are commonly used in industrial automation, based on their levels of complexity and functionality. They are:

Unitary – which is the most basic and simplest type of computing device. It usually uses a single box to contain all of its system components including the processor and its input and output ports.

Modular – which typically consists of several modules that can be clubbed together to form a customized computing device. It has a base module that takes care of regular or core functions including input connections, electrical power monitoring etc. The extra modules are usually signal converters or additional outputs that can be added as per requirements.

Rack Mounting – which is similar to the modular PLC, but differs in that each of the modules is usually distinguished from one another, unlike modular when each of them is connected to the base module. In Rack Mounting, all the additional modules are connected through a network and the modules are organized in the form of racks.


What are the main components of PLC?

Typically, PLCs consist of 6 main components namely, the input and output modules, the power supply, the peripheral or interface components, the coprocessor modules and most importantly, the Central Processing Unit (CPU) which stores and runs the software programs processed by the software unit.

What is Allen Bradley software?

Allen Bradley has been one of the most trusted and reliable names in the field of process automation software since its pioneer in the computing technology. Allen Bradley software basically consists of a group of intelligent and support technologies or products including input and output modules, programmable controllers or PLCs, motor control centres, portable data collectors, sensors and the like that aid industrial automation.

What is Allen Bradley PLC programming?

Allen Bradley PLC programming thus describes the use of Allen Bradley software, more specifically the brand’s PLC in industrial automation. It is symbolized by robustness, reliability and of course high performance. High levels of efficiency are often associated with industries that use Allen Bradley PLC programming, as the brand’s systems are carefully designed to work seamlessly in complex industries.

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Modbus vs Profibus- Advantages of Modbus Over Profibus

In today’s world, there are many different protocols, and some are better equipped to work in different applications. Modbus and profibus each have strengths, and there is some overlap as to what each of them is capable of. Some people, however, consistently prefer to use modbus over profibus.

binary-codeModbus was originally designed in the mid 70’s and was a proprietary protocol for Modicon. The company published it royalty free before finally making it an open protocol. Many companies began using it, and because of this, there are now several variations. Even though it has variants, it is best described as simple. It’s easy to implement and easy to use. This is one of its biggest strengths. The specification document is less than 100 pages, which indicates its simplicity. Modbus usually refers to one of three protocols – Modbus ASCII, Modbus RTU, or Modbus TCP/IP.

Modbus ASCII was the first modbus, and usually runs on the RS-232 or the RS-485 physical layer. There is one master and all slaves are polled on demand by the master. The message frame can be up to 253 bytes.
Modbus RTU is a variation of Modbus ASCII. The difference is the encoding of the data. RTU uses bytes to encode messages, which increases the throughput.
Modbus TCP/IP was added much later, and can be thought of as, essentially, a way of encapsulating an RTU packet within a TCP/IP packet. It’s simple to use, but is slower than other Ethernet products. It is still adequate for monitoring applications.

As Modbus is a simple master slave protocol, and the master has full control of the communication. The slave will only respond when asked. The master will record the outputs, and read the inputs from every slave during every cycle. The slave devices don’t join the network, and they only respond when spoken to, and remain idle when they are not being spoken to. There’s no requirement for a watchdog timer, and there’s no requirement for diagnostics for the slave’s health.

Modbus usually uses the RS232 or the RS485 physical layer, but it can also use other physical layers, like phone lines, or wireless. RS232 and RS485 were established physical layers during the Modbus original development, and it didn’t add any new requirements.

In the case of using phone lines and wireless, Modbus has excelled. Phone lines and wireless introduce delays in the messages, which can be problems, but Modbus either deals with this, or it adapts to work in these applications.

Modbus can be used from a controller, or monitor to a smart device, controller, or monitor to a smart device from multiple vendors and for remote monitoring of information from a smart device.

Profibus is not only more complicated to implement and use, but it also uses specialized characteristics which tie it to RS485. RS485 is used in many different industries but it will become obsolete. Modbus, on the other hand, is always going to grow and be utilized because of its simplicity, and because it can be adjusted to the Ethernet, without overly complicated processes.

However, it is possible to utilize both protocols to work together. Modbus is the data transport between a master controller/data concentrator and has a remote profibus station. Using both protocols allows the simple implementation and easy modem support of modbus, while also gaining some positives from profibus. Profibus can be used in hazardous and multi vendor applications, and modbus provides a link between a SCADA system and a data concentrator.

What is a programmable logic controller?

pROGRAMMABLElOGICcONTROLLERThis is a digital computer which is specially adapted for the control of manufacturing processes such as assembly lines, lighting fixtures, robotic devices, amusement rides or activities that require high-reliability control, process fault diagnosis and ease of programming.

Programmable Logic Controllers (PLCs) have progressively become a fundamental part of the industrial environment. It is imperative to understand their basic functionalities as a technician involved with PLCs controlled processes.

PLCs are designed for multiple arrangements of input and output, resistance to impact and vibration, electrical noise immunity and extended temperature ranges.  The programs are written on a computer and then downloaded to the PLC. The Programs to control machine operation are stored either in non-volatile memory or battery backed up RAM.  A PLC allows for output results in response to input conditions within a set time.

A brief history of the PLC

Before the PLC, sequencing and control for manufacturing were composed of drum sequences, relays, and closed-loop controllers. The process of updating these was expensive and time-consuming because it required individual rewiring of relays.

PLCs were invented to replace the rewiring of relay based control panels in the American automotive industry when there was a change in production models.

GM Hydramatic, which is General Motors automatic transmission division, issued a request in 1968 for the hard-wires relays systems to be replaced. Bedford Associates of Bedford, Massachusetts gave the winning proposal.

Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product which they named MODICON (MOdular DIgital CONtroller). One of the very first 084 models built was decommissioned after almost twenty years of nonstop service. The automotive industry remains one of the largest users of PLCs to date.

Previously, the sequencing and control for automobiles manufacturing relied on hundreds of relays, dedicated closed-loop controllers, drum sequencers, and cam timers. Updating such facilities was costly and time-consuming, as technicians needed to manually and individually rewire the relays.

When digital computers were invented, they were used in in industrial processes to control combinatorial and sequential logic due to their general-purpose programmable devices. However, these early computers required programming specialists as well as rigorous operating environmental control for cleanliness, temperature and power quality. To overcome these challenges, the PLC was developed with several key attributes. It would tolerate a harsh environment; effortlessly support discrete input and output. Also, its operations could be monitored and would not require years of training to use.

Advantages of PLCs

Reduced Cost: PLC prices range from a few hundred to a few thousand. PLCs are cost efficient because they eliminate shipping and installation costs.

Flexibility: A single PLC can effortlessly run many machines.

Ease of Troubleshooting: With PLC control, any changes in sequence or circuit design are as simple as retyping the logic. PLCs allow for a fast and cost effective way of correcting errors. Moreover, a PLC program can be tested after it is developed before it is implemented in the field.

Space Efficient: A PLC requires fewer components than conventional hardware systems making them space efficient.

Visual observation: PLCs have a visual display on a screen which makes troubleshooting simple and fast.

Components of a PLC

All PLCs have the similar basic components. These include controller relay units for input and output, timers, CPU, a peripheral device, communication processor (CP), interface module (IM) and power supply. These components work jointly to carry information into the PLC, evaluate that information after which the information is sent back out to various fields.

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