PLC (Programmable Logic Control)

 Programmable Logic Controllers (PLC) is an electronic computer that is easy to use (user friendly), which has control functions for various types and various levels of difficulty. Definition according Capiel Programmable Logic Controller (1982) is: an electronic system that operates in digital and designed for use in industrial environments, where the system uses a programmable memory for internal storage of instructions that implement specific functions such as logic, sequence , perwaktuan, counting and arithmetic operations to control machines or processes through the modules I / O digital and analog.
Based on his concept of PLC are as follows:
1. Programmable, showed the ability in terms of memory for storing programs that have been created that could easily be altered functionality or usefulness.
2. Logic, shows the capability of processing input arithmetic and logic (ALU), ie, perform compare operations, add, multiply, divide, subtract, negation, AND, OR and so forth.
3. Controller, showing the ability to control and regulate the process so as to produce the desired output.
PLC is designed to replace a series of sequential relay in a control system.

In addition, programmable, this tool can also be controlled, and operated by people who have no knowledge in computer operations in particular. This PLC has a programming language that is easily understood and can be operated when the program was created by using the software in accordance with the type of PLC used was dimasukkan.Alat this work based on inputs available and depending on the circumstances at a certain time which will then ON-OFF or her right outputs. 1 shows that the situation is expected to be fulfilled while 0 means condition not met expected. PLC can also be applied to control systems with output much.
PLC function and usability is very broad. In practice, the PLC can be divided in general and in particular [4]. In general, the function of PLC are as follows:
1. Sequential Control. PLC processing the binary signal input into output that is used for the purposes of processing techniques sequentially (sequential), here the PLC to maintain that all the step or steps in a sequential process takes place in the proper sequence.
2. Monitoring Plant. PLC continuously monitors the status of a system (eg temperature, pressure elevation) and take necessary action in connection with a controlled process (for example, already exceeds the limit value) or displays a message on the operator.
While the function of PLC in particular is able to provide input to the CNC (numerical Computerized Control). Some of the PLC can provide input to the CNC for the benefit of further processing. CNC when compared with the PLC has a higher accuracy, and more expensive. CNC is usually used for the finishing process, forming a workpiece, molding and so forth.
The working principle of a PLC is to accept input signals that controlled the process then do a series of logical instructions to the input signal in accordance with programs stored in the memory then generate output signals to control actuators or other equipment.

Advantages and disadvantages of PLC

In industries that exist today, the presence of the PLC is needed primarily to replace the wiring or cabling system that previously was used in controlling a system. By using the PLC will get many benefits which are as follows:
Ø Flexibility
In the past, each different electronic devices controlled by each controller. For example ten machines require ten controllers, but now with only one tenth the machine PLC can be run with their respective programs.

Ø Changes and error correction system easier
If one of the system will be modified or corrected so pengubahannya only performed on the program contained on a computer, within a relatively short period, after which it was downloaded to the PLC. If not using a PLC, for example relays the amendments made by altering the pengkabelannya. This course takes a long time.

Ø The number of contacts that many
Number of contacts held by the PLC on each coil is much more than that owned by a contact relay.

Ø The price is cheaper
PLC is capable of simplifying a lot of cabling compared to a relay. So the price of a PLC at a price cheaper than some fruit relay capable of doing the wiring for the same amount with a PLC. PLC include relays, timers, counters, sequencers, and various other functions.

Ø Pilot Running
PLC is programmed to run and evaluated in the office or laboratory. The program can be written, tested, and modified diobserbvasi when necessary and this saves time when compared with a conventional relay system was tested with best results at the plant.

Ø Visual Observation
During the program starts, the operation of the PLC can be viewed on a CRT screen. Mistakes of any operation can be observed when there.

Ø Operating Speed
PLC operation speed faster than the relay. PLC velocity determined by time in units of milliseconds scannya.

Ø Ladder or Boolean Programming Method
PLC programming can be stated with ladder programming for technicians, or Boolean algebra for the programmer who works in digital control systems, or Boolean.
Ø In character-tested
Solid state devices are more resistant than the relay and test the mechanical or electrical timers. PLC is a solid-state devices that are more resistant test.

Ø Simplifying the control system components
The PLCs also have counters, relays and other components, so that does not require components such as additional. Use of relays requires counters, timers or other components as additional equipment.

Ø Documentation
Printout of the PLC can be directly obtained and do not need to see the blueprint of his circuit. Unlike the printout relay circuit can not be obtained.

Ø Security
Changing the PLC can not be made unless the PLC is not locked and programmed. So there is no unauthorized person can change the PLC program for a PLC is locked.

Ø Able to change by the reprogramming
Karena PLC can be quickly re-programmed, mixed with the production process can be completed. For example part B will be executed but sections of A is still in the process, the process in section B can be re-programmed in seconds.

Ø Addition of faster circuits
Users can add a circuit controller at any time quickly, without requiring great effort and cost as in conventional controllers.

Besides the benefits mentioned above, there are losses that are owned by the PLC, namely:
Ø The technology is still new
Changing the old control system using relay ladder or to a PLC computer concept is difficult for some people

Ø Bad for application programs that remain
Some applications are applications with a single function. While the PLC may include several functions at once. In applications with a single function are rarely carried out not even change at all, so the use of PLC in applications with a single function will waste (cost).

Ø Environmental Considerations
In a processing environment may be experiencing high heat, vibration is in direct contact with electrical appliances within the PLC and this is when there constantly, thus disrupting the performance of the PLC is not functioning optimally.

Ø Operating with a fixed circuit
If the circuit in an operation are not changed then the use of more expensive PLC compared with other control equipment. PLC will become more effective if the programs on the process to be upgraded periodically.

to be continued to Part2

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