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Programmable Logic Controllers: Industrial Control programmable logic controller (PLC) and a consequential revolution of. This chapter Programmab. () PLC-TEXT. Library of Congress Cataloging-in-Publication Data. Bryan, L.A. . Programmable controllers: theory and implementation/L.A. Bryan,. E.A. Bryan. The abbreviation “PLC” means Programmable Controller. “PC” is used, how- ever, in some CX-Programmer displays to mean Programmable Controller.

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The First Programmable Logic. Controllers (PLCs). • Introduced in the late 's. • Developed to offer the same functionality as the existing relay logic systems. PDF | On Jul 1, , Mallikarjun G Hudedmani and others published Programmable Logic Controller (PLC) in Automation. Programmable logic controllers (PLCs) have been used in industry in one form or another for the past twenty over years. The PLC is designed as a replacement.

Order No. Bliesener, F. Ebel, C. Plagemann, H. Regber, E.

Even within the same product line of a single manufacturer, different models may not be directly compatible. Control example shown in ladder diagram[ edit ] This is a programming example in ladder diagram which shows the control system.

A ladder diagram is a method of drawing control circuits which pre-dates PLCs. The ladder diagram resembles the schematic diagram of a system built with electromechanical relays. As an example, say a facility needs to store water in a tank. The water is drawn from the tank by another system, as needed, and our example system must manage the water level in the tank by controlling the valve that refills the tank.

Shown are: Two inputs from the low and high level switches represented by contacts of the float switches An output to the fill valve, labelled as the fill valve which it controls An "internal" contact, representing the output signal to the fill valve which is created in the program. A logical control scheme created by the interconnection of these items in software In ladder diagram, the contact symbols represent the state of bits in processor memory, which corresponds to the state of physical inputs to the system.

Pdf programmable logic controller

If a discrete input is energized, the memory bit is a 1, and a "normally open" contact controlled by that bit will pass a logic "true" signal on to the next element of the ladder. Therefore, the contacts in the PLC program that "read" or look at the physical switch contacts in this case must be "opposite" or open in order to return a TRUE for the closed physical switches. Internal status bits, corresponding to the state of discrete outputs, are also available to the program.

In the example, the physical state of the float switch contacts must be considered when choosing "normally open" or "normally closed" symbols in the ladder diagram. Both float switches normally closed open their contacts when the water level in the tank is above the physical location of the switch. When the water level is below both switches, the float switch physical contacts are both closed, and a true logic 1 value is passed to the Fill Valve output.

Programmable Logic Controllers | Wiley Online Books

Water begins to fill the tank. The internal "Fill Valve" contact latches the circuit so that even when the "Low Level" contact opens as the water passes the lower switch , the fill valve remains on. Since the High Level is also normally closed, water continues to flow as the water level remains between the two switch levels.

Once the water level rises enough so that the "High Level" switch is off opened , the PLC will shut the inlet to stop the water from overflowing; this is an example of seal-in latching logic. The output is sealed in until a high level condition breaks the circuit.

After that the fill valve remains off until the level drops so low that the Low Level switch is activated, and the process repeats again. A complete program scan may take only a few milliseconds, much faster than changes in the controlled process. Programmable controllers vary in their capabilities for a "rung" of a ladder diagram.

Some only allow a single output bit. There are typically limits to the number of series contacts in line, and the number of branches that can be used. Each element of the rung is evaluated sequentially. If elements change their state during evaluation of a rung, hard-to-diagnose faults can be generated, although sometimes as above the technique is useful.

Some implementations forced evaluation from left-to-right as displayed and did not allow reverse flow of a logic signal in multi-branched rungs to affect the output. Functionality[ edit ] 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. Desktop computer controllers have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than 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 execution, 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. Discrete inputs are given a unique address, and a PLC instruction can test if the input state is on or off. Just as a series of relay contacts perform a logical AND function, not allowing current to pass unless all the contacts are closed, so a series of "examine if on" instructions will energize its output storage bit if all the input bits are on.

Controller programmable pdf logic

Similarly, a parallel set of instructions will perform a logical OR. In an electro-mechanical relay wiring diagram, a group of contacts controlling one coil is called a "rung" of a "ladder diagram ", and this concept is also used to describe PLC logic. Some models of PLC limit the number of series and parallel instructions in one "rung" of logic. The output of each rung sets or clears a storage bit, which may be associated with a physical output address or which may be an "internal coil" with no physical connection.

Such internal coils can be used, for example, as a common element in multiple separate rungs. Unlike physical relays, there is usually no limit to the number of times an input, output or internal coil can be referenced in a PLC program.

Some PLCs enforce a strict left-to-right, top-to-bottom execution order for evaluating the rung logic. This is different from electro-mechanical relay contacts, which in a sufficiently complex circuit may either pass current left-to-right or right-to-left, depending on the configuration of surrounding contacts.

The elimination of these "sneak paths" is either a bug or a feature, depending on programming style. More advanced instructions of the PLC may be implemented as functional blocks, which carry out some operation when enabled by a logical input and which produce outputs to signal, for example, completion or errors, while manipulating variable internally that may not correspond to discrete logic.

Timers and counters[ edit ] The main function of a timer is to keep an output on for a specific length of time.

Introduction to Programmable Logic Controllers

A good example of this is a garage light, where you want power to be cut off after 2 minutes so as to give someone time to go into the house. A Delay-OFF timer activates immediately when turned on, counts down from a programmed time before cutting off, and is cleared when the enabling input is off.

A Delay-ON timer is activated by input and starts accumulating time, counts up to a programmed time before cutting off, and is cleared when the enabling input is turned off.

A Delay-ON-Retentive timer is activated by input and starts accumulating time, retains the accumulated value even if the ladder-logic rung goes false, and can be reset only by a RESET contact.

Logic controller pdf programmable

Counters are primarily used for counting items such as cans going into a box on an assembly line. This is important because once something is filled to its max the item needs to be moved on so something else can be filled. Many companies use counters in PLC's to count boxes, count how many feet of something is covered, or to count how many pallets are on a truck.

Up counters count up to the preset value, turn on the CTU CounT Up output when the preset value is reached, and are cleared upon receiving a reset. Down counters count down from a preset value, turns on the CTD CounT Down output when 0 is reached, and are cleared upon reset.

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These small devices are typically made in a common physical size and shape by several manufacturers, and branded by the makers of larger PLCs to fill out their low end product range. NO and NC symbols each have discussion, problem based learning, case study, structured specific addresses are used as needed and certain functions group learning, etc.

It purpose to make it easier for engineer socializing the knowledge attractively, carefully, accurately, or electrician in the PLC programming [29].. PLC controller and correctly [21]. To adjusting the industrial development, the focus of discussion in this papper 5. PLC subject have four hours in one week of formal lectures, and one hour is fourty five minute. Communication Ninety five for Theories and ninety five minute for practicum. Progammer [23].

Then the students are asked to install software on the laptop and PC in the lab. After that students guided by teachers for the basic installation of PLC.

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Logic controller pdf programmable

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Programmable logic controllers

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