Troubleshooting of PLC SCADA system

Prior to beginning a system start up procedure, it is important to check and verify that PLC system has been installed according to the manufacturers specifications and that the installation meets local, state and national codes. Special attention should be given to system grounding.

Before applying power to the PLC controller, following is to be ensured:

• Check all power and communication cables to ensure that connector pins are straight and not bent or pulled out.
• Connect all cables making sure that connectors are fully inserted into their sockets. Secure connectors as applicable.
• Ensure that all modules are securely held in the I/O rack.
• Place PLC System processor key switch to a safe position.

Apply power and observe processor indicator light for proper indication. When power is applied and safety switch is closed, the power supply should provide the necessary DC voltage for the processor and I/O rack. If the proper voltage is present, the input indicator LEDs of the input modules will function. Any input device that is closed or ON will have an illuminated LED.

Testing PLC Inputs PLC input module should illuminate. Failure of a LED TO illuminate indicates:

• Improper input device operation
• Incomplete or incorrect wiring; check to be sure that the input device is wired to the correct input module and proper channel.
• Loss of power to the PLC input device
• Defective LED or input module

Testing PLC outputs before testing output devices, it must be determined which devices can safely be activated and which devices should be disconnected.

The second method uses the force function of the PLC system to energize outputs, one at a time. This allows the user to turn an output device ON and OFF without using a push button or other contacts.

For final system checkout, the following steps should apply:

• Place the processor in the program mode
• Clear the memory of any previous rung used for testing.
• Using a programming device, enter the program (ladder diagram) into memory.
• Place the processor in the test or disable output mode, depending on the PLC system and verify correctness of program.
• Once the circuit operation has been verified in the test or disable output mode, the PLC processor can be placed in the run mode for final verification.
• Make changes to the program as required (timer setting, counter presets etc.)
• Once the circuit is in final form and the machine or process is running correctly it is recommended that a copy of the program be made.

Troubleshooting

Systematic approach towards PLC troubleshooting should consist of the following steps:

• Symptom recognition
• Isolate the problem
• Corrective action

The status lights of a typical PLC system with built-in power supply indicate:

• DC Power ON if this LED is not lit, there is a fault in the DC power supply. Check the power supply fuse or incoming power.
• Mode indicates which operating mode the processor is in (Run, test, program etc.). The fault may simply be that the key switch is in the wrong position.
• Processor fault when this status light is on
• Memory fault this status light illuminates when a parity error exists in transmission of data between the processor module and memory module. Replace only one module at a time.
• I/O Fault this light indicates a communication error between the processor and the I/O rack.

Some PLC manufacturers offer deluxe output modules that have two indicator LEDs. One indicates that the logic from the PLC processor has been received to turn on the output: the second LED comes on when the triac or power transistor has been turned ON. Similar to the deluxe output modules, there are also input modules that have two indicating LEDs. The first LED indicates that the input device has closed and a voltage signal has been received by the input module; the second LED indicates that the status of the input device ON has been communicated to the processor. 

 

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Analogy to understand Distributed Control System

DISTRIBUTED CONTROL SYSTEM, THE CONCEPT

Distributed control systems (DCS) use decentralized elements to control distributed processes or manufacturing systems specifically continuous process operations. Advantages of DCS are as follows:

· Flexibility

· Equipment long life

· Further modification and improvement in the plant

· Centralized maintenance

The basic idea behind DCS is that there are multiple controllers within the industrial plant and are connected to the central intelligence system through industrial network protocol as per the requirement and other constraints. DCS enables the engineer to control, monitor and report of every individual component or process from a central location.

Redundancy elements are necessary in DCS as to avert any dangerous situation in which we don’t like compromise with safety of life and infrastructure within the plant. Reliability of the system improves as a byproduct of adding redundant components.

DISTRIBUTED CONTROL SYSTEM, THE ANALOGY

Consider an engineering college, where the Director is responsible to run the whole college. Not let us assume that there no head of the departments in the college or if there are heads but they don’t have any administrative power.

Now in this case if any student wants a leave or has any issue on that specific day when Director is not available in the college and Director has also not nominated any other person like Dean or Deputy Director in his absence to work as an acting director, then the student will not be able to get his leave technically.

But if Director has appointed the heads and also has given the rights to exercise administration within their role then there will be no problem of any kind related to administration.

Similarly in DCS as mentioned above, there are multiple controllers within the industrial plant and are connected to the central intelligence system through industrial network protocol as per the requirement and other constraints.

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Image Processing using MATLAB

Image processing using MATLAB has been very often used activity used for computation and data analysis. This article describes how image processing is done using OpenCV library, article also is about basic image processing operations using MATLAB, which is widely used by students and engineers in this field. MATLAB is a high performance language for technical computing. It is used for Maths calculations/ computation, data analysis, algorithm development, modelling stimulation and prototyping. Edge detection, noise modelling, and image histogram modelling basic tools in image processing feature of MATLAB.

Edge Detection: An image is the mapping of intensity of light. We can detect these edges using MATLAB commands. There are many methods for edge detection such as Robert’s operator, Sobel operator, Canny edge detector and so on.

Noise: In image processing, noise in just like a digital image generated during image acquisition and also during transmission. We can use different types of noise as special effects in an image using MATLAB.

Histogram modelling: a histogram of an image provides a vast description of the image. In this program, we plot the histogram on the original image and of the histogram equalized image.

Testing: MATLAB program is run straightforward. There are 3 .m files, one each for edge detection, noise effects, and histogram. Two .JPEG image files are also included along with these .m files in the same folder. Launch MATLAB from your desktop and open an .m file and run the program. Image processing is a diverse and most useful field of science in MATLAB. This article highlights basic image processing using MATLAB. Many useful topics can be applied using MATLAB or OpenCV library such as erosion, degradation, smoothing, restoration, segmentation, dilation, point processing, line processing and edge detection of images.

MATLAB based GUI Graphical user interface for digital image watermarking

GUI (Graphical user interface) based watermarking system required a login password for authentication. In the absence of correct password no one will be able to access the program and GUI (Graphical user interface) panel.

In order to run the application you need a 32 or 64 bit operating system with MATLAB software, a cover image and a logo/watermark image. In this project, GUI (Graphical user interface) panel/program is quite user friendly.

Software

The application program has been developed in MATLAB. This will give you to access the main GUI (Graphical user interface) panel. But an incorrect password closed the GUI (Graphical user interface) panel/program. The watermark image will be generated on pressing ‘assemble/embedded watermark’ button. The similarity between cove image and watermarked image is evaluated by calculating the peak signal to noise ration and mean square error values.

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From relays to intelligent Industrial automation

Today Industrial automation control/ automated processes from production lines to waste water treatment facilities and infrastructure systems are one control system on one network. Evolution of Intelligent industrial automation has taken more than 40 years that began in 70s. Technology innovation has taken leaps in each decade, initiating developments of simple automation to intelligent automation, and from electronics to IT. Intelligent industrial automation creates great business value for all kinds of firms who face the challenges of high wages and production costs. Without intelligent automation, many more manufacturing companies would have been forced to migrate to lower cost countries.

The infrastructure has become modernized, and industrial automation based automated solutions with built-in intelligence make everything from water treatment facilities to bridges and hospitals run more efficiently.

There has been a journey to reach this far. The first major step toward Industrial automation was programmable controllers called PLC that replaced enormous relay boards which could take electricians thousands of hours to hardwire, start up, troubleshoot and update. Programmable logic controllers, or PLCs, often are made by principal manufacturers like Allen-Bradley, Siemens, Modicon, Mitshubishi, Omron, Delta etc. pioneers in this field. As technology progressed, engineers were able to easily program control systems and make production processes much more efficient. In the beginning, PLCs were costly so only a few companies were able to afford, as their electronic components were expensive, but more and more companies replaced relay boards with PLCs as prices came down in 80s.

PLC manufacturers dominated the market, they developed their own proprietary protocols, fieldbuses and networking standards. Throughout the 90s, however, Ethernet emerged as the sole standard. Thus, IT departments are now involved in production processes and helping to support the network.

As PLCs evolved, many new intelligent industrial automation products/devices have arrived on the scene to become part of industrial automation solutions. Frequency drives, robots, cameras for vision systems, RFID readers and other process instruments now share the same control systems and programming languages. Today, there is one network one control system. Industrial automation Process control has become faster and simpler, and it has become easier to scale solutions that work in both small and large plants. Companies today are using just one network for both their Windows platform and data, and this offers a number of challenges. There are potential risks that require attention is that of hackers stealing/disrupting into production data and doing damage. Network Security will thus be an issue that will require our full attention in coming years.

 

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