Programmable Logic Controller (PLC) V2

PLC (Programmable Logic Controller) is a microprocessor-based controller can be programmed. PLC is also a RISC-based systems (Reduced Instruction Set Computer) so that only require a simple and limited commands. PLC provides many tools of I / o programmable and capable of handling a lot of process control devices in I / o who has.In 1978, the National Electrical manufactures Association (NEMA) sets standards of this programmable control (standard NEMA ICS3-1978, part ICS3-304). NEMA defines the PLC as follows: "electronic equipment that operates digitally, using a programmable memory for internal storage for instructions that implement specific functions, such as logic, sequence, timing, and arithmetic, as well as to control the machine- machine or process that includes input modules, or both analog and digital outputs, from various types of machine or process.

Originally designed to replace the PLC or relay logic circuit, by adding arithmetic functions, timers, and counters, which are widely used and is a major part in controlling the complex system or process. A PLC is designed to be able to replace the tens to hundreds of logic control circuit which does not hang together. Standard conditions PLC inputs and outputs are designed to allow direct connection to the mover machines, production machines or with a sensor.
Also developed are also several additional capabilities that can be used on PLC in the form of additional modules, such as:
 Analog I / O,
 PID Controller
 Communication,
 Graphic Display,
 Additional I / O, and
 Additional Memory.

Currently, the PLC is increasingly widely used in industry to solve the problems of automatic control. This is due to PLC has several advantages, among others:
 ease of installation because it is not long to build a control system.
 simplicity in system development and modification.
 the simplicity in programming.

Advantages and disadvantages of PLC
In industries that exist today, the presence of the PLC is needed primarily to replace wiring or cabling system that previously was used in controlling a system. By using the PLC will get many benefits which are as follows:
1. Flexible
In the past, each different electronic devices controlled by each controller. Suppose ten machines require ten controllers, but now with only one tenth PLC machine can be run with each program.
2. Changes and error correction system easier
If one system will be modified or corrected so pengubahannya only done on the programs contained in computers, in a relatively short time, after that it 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.
3. The number of contacts that many
Number of contacts held by PLC in each coil is more than a contact that is owned by a relay.
4. 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.
5. Plot 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.
6. 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 the error occurred.
7. Operating speed
PLC operation speed is faster than the relay. PLC velocity determined by time in units of milliseconds scannya.
Ladder Programming Method or Boolean
PLC programming can be stated with ladder programming for technicians, or Boolean algebra for the programmer who works in digital control systems, or Boolean.
9. Resistant character test
Solid state devices are more resistant than the relay and test the mechanical or electrical timers. PLC is a solid state device that is more resistant test.
10. Simplifies the control system components
The PLC also have counters, relays and other components, so it does not require components such as additional. Use of relays requires counters, timers or other components as additional equipment.
11. 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.
12. Security
Changing the PLC can not be done unless the PLC is not locked and programmed. So there is no unauthorized person can change the PLC program for a PLC is locked.
13. Can make changes by reprogramming
Since the PLC can be programmed quickly reset, the production process that mixes 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.
14. 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:
1. The technology is still new
Changing the old control system using relay ladder or to a PLC computer concept is difficult for some people.
2. Bad for the 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).
3. Environmental considerations
In a processing environment may be experiencing high heat, vibration is in direct contact with electrical appliances within the PLC, and this when the occur continuously, interfering with the performance of the PLC that is not functioning optimally.
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 be more effective if the program on the process to be upgraded periodically.