PLC Parts
PLC system consists of five main parts, namely:
Ø Central processing unit (CPU). This section of the brain or heart PLC, because this section is the part that perform operations / processing program stored in the PLC. Besides, the CPU also controls all the operational work of the PLC, the transfer of information between the PLC through the internal bus, memory and the unit I / O. Part of this CPU include: q Power Supply, power supply, change the input supply electricity into the electricity supply in accordance with CPU and the entire computer. q Alterable Memory, composed of many parts, the point of this part of the contents in place the chip on chip RAM (Random Access Memory), but the contents can be modified and deleted by the user / programmer. If there is no electricity supply to the CPU then the contents will be lost, and therefore this section is called be volatile, but there are also non-volatile part. q Fixed Memory, contains a program that is set by the manufacturer PLC, made in the form of a special chip called a ROM (Read Only Memory), and can not be modified or removed during the operation, the CPU, so this section is often called non-volatile memory that will not erased its contents, although there is no electricity coming into the CPU. Moreover, it can also add modules or Electrically Erasable EEPROM Programmable Read Only Memory which is intended to back up the main program RAM processor so that the processor can be programmed to load into RAM EEPROM program if the program in RAM is lost or damaged [6]. q Processor, is the part that controls so that information remains that way from one section to another section, this section contains a series of clock, so that each transfer of information to another place in time right up until q Battery Backup, CPU generally have this section. This section serves to maintain that no loss program that has been put into RAM when the PLC to PLC power supply was suddenly interrupted.
Ø Programmer / monitor (PM). Programming done via the keyboard so that the tool is called the Programmer. With the Monitor, it can be seen what is typed or processes being executed by the PLC. The form of this PM there is a big like a PC, there is also a small-sized hand-Eld programmer with a small display window, and there is also a form of laptop. PM associated with the CPU via a cable. Once programmed, the CPU completed PM no longer used for the operation of the PLC process, so this section is only needed one for a lot of CPU.
Ø Module input / output (I / O). Input is the part that receives electrical signals from sensors or other components and the signals were fed to the PLC to be processed. There are many types of input modules which can be selected and the type depends on the input that will be used. If the input is the limit switches and pushbutton selectable DC input card. Analog input module is a special input card that uses the ADC (Analog to Digital Conversion) in which this card is used for input in the form of variables such as temperature, velocity, pressure and position. In general there are 8-32 input point from each module input. Each point will be marked as a unique address by prosesor.Output is part of the PLC which channel the electrical signal processing results of the PLC to the output equipment. The quantity of information / electrical signal that is indicated by the voltage between 5-15 volts DC, with information outside the system voltage varies between 24-240 volts AC DC mapun. Output cards usually have a 6-32 in a single-point output module. Analog output card is a special type of module that uses the output DAC (Digital to Analog Conversion). Analog output module can retrieve the value in 12 bit and turn it into an analog signal. This signal is usually 00-10 volts DC or 4-20 mA. Analog signals are usually used in equipment such as motor-operated valves and pneumatic position control devices.Bila required, an electronic system can be added to this module connects to a distant place. The process of actually operating under the control of PLC may be far away, can be thousands of meters.
Ø Printer. This tool allows the program to the CPU can be in the printout or printed. The information may be printed is the ladder diagram, the status registers, status and a list of conditions that are executed, the timing diagram of the contacts, the timing diagram of the registers, and others.
Ø The Program Recorder / Player.
This tool is used to store programs in the CPU. In the old PLC used tape, floppy disk system. Now this growing PLC with the hard disk that is used for programming and recording. Programs that have been recorded this will be recorded back into the CPU when the original program is lost or encounter an error.
For large operations, another possibility is to connect the CPU with the main computer (the master computer) that are usually used in large factories or processes ordinate many PLC System.
Concept Design of Control System with PLC [7] [8]
In designing a control system requires systematic approaches to the procedure as follows:
1. Draft Control System
In this phase the designer must first determine what system will be controlled and the process of how that may be taken. The system can be controlled machine tools or integrated process which is often generally referred to as a controlled system.
2. Determination of I / O
At this stage all external input and output devices to be connected to the PLC must be determined. Input device may include switches, sensors, valves and other devices while the output can be either electromagnetic solenoid valves and others.
3. The Design Program (Program Design)
After the specified input and output then continued with the process of designing the program in the form of ladder diagrams to follow the rules and sequence control system operation.
4. Programming (programming)
5. Running System (Run The System)
At this stage needs to detect the existence of the errors one by one (debug), and examine carefully until we ensure that the system is safe to run.
in addition to functions that have been told before ... PLC in use also for the Emergency Shutdown System (ESD) due to the rapid response compared to DCS ....
The following is the type of PLC-Programming based on IEC 61131-3 .. there are five programming languages that are recognized by this standard ..
- Ladder Diagram (LD)- Function Block Diagram (FBD)- Instruction List (IL)- Structure Text (ST)- Sequential Function Chart (SFC)
The most often used is LD I prefer ... but if pake FBD.Indeed depend on the background is ... if people are more familiar with LD power ... because the initial design of the PLC is to replace conventional systems that relay his buanyak really wire .... Whereas if college kids are usually more pleased FBD because it is usually already familiar with Digital System (Block Diagram AND, OR, etc.)
- Manufacturer or PLC-makers including the following:
- Allen Bradley (www.ab.com)
- Schneider Electric (http://www.telemecanique.com/en/functions_discovery/function_5_11.htm)
- Mitsubishi
- GE Fanuc
- etc
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