Types of Programmable Logic Controllers

Programmable logic controllers (PLCs) has several types. Based on the size of the module, type PLC divided into several types:

1. Micro PLC or Small PLC:- It is the simplest PLC with the power supply module, CPU, I / O modules and communication ports in a single chassis. This PLC types are usually limited to a few I / O discrete and can be expanded. There are various micro PLCs on the market today. The vast majority offer analog I / O. with just about any micro PLC, or for that matter PLC in general, when the application requires the monitoring of various analog signals, a separate module is required for each signal (voltage, current, temperature). Examples of this type are CP1H Omron, Siemens S7-200, Fuji Electric SPB.

2. Medium PLC:- is PLC which has CPU module, I / O or communication port are separately. Each module is connected by connector or backplane. It has the capacity more than 2000 I / O. Examples of this type are Omron CS1, Siemens S7-300.

3. Large PLC:- This kind of PLC is nearly equal to the medium one but it has large I/O capacity and more able to be connected with the higher control systems. Examples of this type are CVM1 Omron, Siemens S7-400.


Based on the type of input PLC / output PLC can be divided into:-

1. Discrete I / O, It is a logic shaped digital input and output as high level with 24VDC, or low level with 0V or as a relay contact output that can be irrigated up to 240VAC.

2. Special I / O, it is I / O that has special functions such as.
a. Analog Input Modules
b. Modules temperature PT100 module or thermocouple (low-level analog inputs)
c. High Speed Counter Module is a frequency logic with generally high level 5V, 12V or 24V.
d. Fuzzy Logic Module
e. PID Module
f. Servo Module
g. Communication protocol module form made by each manufacturer, for example, Fieldbus, Modbus, Profibus, Ethernet, Sysmac way, Device Net, Control Net.
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