Main parts of PLC (Programmable Logic Controller) : -
PLC have many input terminals through which communicate high and low logical state from switches and sencors. It also has many output terminals also.
Input – input are basically controlling elements of output. There are three types of inputs.
- Digital Input – all discrete value signal input are known as digital input. Digital input having two states either ‘OFF’(0) or ‘ON’(1). All switching and sensing devices belongs to digital I/Ps.
Ex: Start PB, Stop PB, Emg Stop, L/S, Pressure S/W, Float Switch, Proximity Sensors, Photo Electric sensors etc.
- High Speed Input – these are similar to digital input only the difference is of switching frequency. If the switching frequency of input is increases to normal sequencly the input elements belongs to high speed input.
- Analog Input – All types of value variable signals, continuous value signal elements ormore
than binary status known as analog input.
Ex – Transducer, thermocouple, Photo cell etc.
- Output – Output is the end of any function or instruction it is load type device.
Types : a)
Digital b)High Speed c) Analog
- Digital Output –All types of discrete value signal outputs are known as digital output.
- High Speed Output – these are similar to digital but pulse frequency rate is higher.
- Analog Output – All types of continuous value signal output belongs to analog output.
- Memory – memory is used for holding the data & backup of data. Memory is the space In software & it is made by memory registers.
- Memory Capacity – memory capacity depends on total quantity of registers & types of registers.
- Memory bit – It is the smallest unit of digital electronics memory bit having binary status
means two either 0 or 1.
- Memory Registers – Memory registers are made by memory bits. These are also known as memory parameters.
Types of Memory Registers :–
Octal (byte) – 8 Bit register.
- Decimal – 10 Bit register
- Hex. Decimal – 16 Bit register
Types of Memory :–
- RAM – Random Access Memory
It is volatile in nature
It is Non – Volatile in nature
- EPROM – Erasable Programmable Read Only Memory For Removing the data EPROM
Cassette has to be placed in front of ultra violet rays for 15 minutes, the
complete data will be washed out. Data can’t be changed at site for changing
data EPROM Cassette has taken out from panel & carry it in any lab.
- EEPROM - Electrical Erasable Programmable Read Only Memory It is micro chip already fixed in card the editing will be done at sight. Its speed is high.
- FLASH PROM – Its Speed is faster than EEPROM.
CPU – Central Processing Unit (CPU)
Microprocessor based, may allow arithmetic operations, logic operators, block memory
moves, computer interface, local area network, functions, etc. CPU makes a great number of check-ups of the PLC controller itself so eventual errors would be discovered early.CPU replaces contactors, timers, counters
of RLC by software.
Power supply -
Most PLC controllers work either at 24 VDC or 220 VAC. Some PLC controllers have electrical supply as a separate module, while small and medium series already contain the supply module. Power supply is used for supplying the diff. supply voltages to diff. PLC sections.