PLC Hardwere configuration

Many PLC configurations are available, even from a single vendor. But, in each of these there
are common components and concepts. The most essential components are:
Power Supply - This can be built into the PLC or be an external unit. Common voltage levels
required by the PLC (with and without the power supply) are 24Vdc, 120Vac, 220Vac.
CPU (Central Processing Unit) - This is a computer where ladder logic is stored and processed.
I/O (Input/Output) - A number of input/output terminals must be provided so that the PLC can
monitor the process and initiate actions.
Indicator lights - These indicate the status of the PLC including power on, program running, and
a fault. These are essential when diagnosing problems.
The configuration of the PLC refers to the packaging of the components. Typical configurations
are listed below from largest to smallest as shown in Figure 14.
Rack - A rack is often large (up to 18” by 30” by 10”) and can hold multiple cards. When necessary,
multiple racks can be connected together. These tend to be the highest cost, but also the
most flexible and easy to maintain.
Mini - These are smaller than full sized PLC racks, but can have the same IO capacity.
Micro - These units can be as small as a deck of cards. They tend to have fixed quantities of I/O
and limited abilities, but costs will be the lowest.
Software - A software based PLC requires a computer with an interface card, but allows the
PLC to be connected to sensors and other PLCs across a network.

Automatic Gates using PLC

Information on Drawing Numbers for Automatic Gates using PLC :
1. Area Sensor (If there are objects, the sensor output OFF)
2. Area Sensor (If there are objects, the sensor output OFF)
3. Area Sensor (If there are objects, the sensor output OFF)
4. Area Sensor (If there are objects, the sensor output OFF)
5. Electric Motor And Gearbox
6. Limit Switch for Open gate condition
7. Limit Switch for Closed gate conditions
8. Gate


Number Of Inputs and Output PLC applied :
1. Number Of Inputs PLC is 6 Input :
--- 4 Unit Input for Area Sensor 1,2,3,and 4.
--- 1 Unit Input for Limit Switch for Open gate.
--- 1 Unit Input for Limit Switch for Closed gate.
--- Total Number Of Inputs PLC is Minimum 6 Input Unit.

2. Number Of Output PLC is 2 Output :
--- 1 Unit Output to contactor for Electric Motor (Open Gate ).
--- 1 Unit Output to contactor for Electric Motor (Close Gate ).
--- Total Number Of Outputs PLC is Minimum 2 Output Unit.


Sequence PLC Programming for Automatic Gates :

1. Open Gate
a. If Area Sensor 1 = OFF Then Electric Motor for Open Gate = ON.
b. If Limit Switch for Open gate = ON Then Electric Motor for Open Gate = OFF.
c. Electric Motor for Close Gate = always OFF

2. Close Gate
a. If Area Sensor 4 = OFF AND Area Sensor 2 = ON AND Area Sensor 3 = ON Then Electric Motor for Close Gate = ON.
b. If Electric Motor for Close Gate = ON AND Area Sensor 2 = OFF OR Area Sensor 3 = OFF Then Electric Motor for Close Gate = OFF AND Electric Motor for Open Gate = ON.

Note : For All Area Sensor : If there are objects, the sensor output OFF

GE Substation Automation Components

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