ITSC Automation services-Ethiopia

I wonted to insure as the company ,that I keep my PLC training experience current and kept in touch with my customers first hand

A programmable logic controller, PLC or programmable controller is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines.
PLCs were designed to replace relay logic systems. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver.

Modern PLCs can be programmed in a variety of ways, from the relay-derived ladder logic to programming languages such as specially adapted dialects of BASIC and C. Another method is State Logic, a very high-level programming language designed to program PLCs based on state transition diagrams.

Many early PLCs did not have accompanying programming terminals that were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some version of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more common for ladder logic to be used, for the aforementioned reasons and because it was a familiar format used for electromechanical control panels. Newer formats such as State Logic and Function Block (which is similar to the way logic is depicted when using digital integrated logic circuits) exist, but they are still not as popular as ladder logic. A primary reason for this is that PLCs solve the logic in a predictable and repeating sequence, and ladder logic allows the programmer (the person writing the logic) to see any issues with the timing of the logic sequence more easily than would be possible in other formats. PLCs, up to the mid-1990s, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs.[2] Some proprietary programming terminals displayed the elements of PLC programs as graphic symbols, but plain ASCII character representations of contacts, coils, and wires were common. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were minimal due to lack of memory capacity. The very oldest PLCs used non-volatile magnetic core memory.

More recently, PLCs are programmed using application software on personal computers, which now represent the logic in graphic form instead of character symbols. The computer is connected to the PLC through Ethernet, RS-232, RS-485 or RS-422 cabling. The programming software allows entry and editing of the ladder-style logic. Generally the software provides functions for debugging and troubleshooting the PLC software, for example, by highlighting portions of the logic to show current status during operation or via simulation. The software will upload and download the PLC program, for backup and restoration purposes. In some models of programmable controller, the program is transferred from a personal computer to the PLC through a programming board which writes the program into a removable chip such as an EEPROM or EPROM.
Functionality
The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications. Desktop computer controllers have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than do PLCs, and because the desktop computer hardware is typically not designed to the same levels of tolerance to temperature, humidity, vibration, and longevity as the processors used in PLCs. Operating systems such as Windows do not lend themselves to deterministic logic ex*****on, with the result that the controller may not always respond to changes of input status with the consistency in timing expected from PLCs. Desktop logic applications find use in less critical situations, such as laboratory automation and use in small facilities where the application is less demanding and critical, because they are generally much less expensive than PLCs

3 Way Switch Wiring Diagram

Every input and output has an absolute address predefined by the hardware
configuration. This address is specified directly; that is, absolutely.
The absolute address can be replaced by any symbolic name you choose.

SIMATIC S7-400
The Power PLC for system
solutions in the manufacturing
and process industries
■ Rack system with different subracks
■ Extremely high-speed processing and communication
performance
■ Changes to the configuration during operation
■ Isochronous mode via PROFIBUS
■ Fail-safe and fault-tolerant

Siemens AG
Automation and Drives
Industrial Automation Systems

Control of fast processes with isochronous mode
Distributed solutions with isochronous mode guarantee a
very high accuracy as well as a fast and reliable processing
sequence. This is particularly important for controlling
drives.
Processing cycles are synchronized to control fast machines in
production and machining processes operating at high-speed,
i.e. the cycle for certain operations is synchronized and
embedded in a fixed time grid – the system clock. The processing
sequences are provided with continuity, and can therefore
be solved rapidly and reliably.
Process response times that are reproducible and defined are
required in order to implement this. This means that I/O signals
have to be read in an equidistant time grid, out-put, and
synchronized with the user program.
Siemens AG
Automation and Drives
Industrial Automation

PLC certification must be with real PLCs, employees must be evaluated in the use of best-practices by a live instructor!

As a technician, we should know where and how to put the overload protection.It is connected only under of each motor contactors. And only you need to know is the connection of normaly closed protection of over load protection going to the coil of its motor contactors..

Influence and Reliability Reliability professionals today have a challenge. Engineering and operations staff members are taught to think for themselves, to make decisions, to get things done. The entire staff is highly...