The conguration of programmable controller is shown in Fig. 1-1. Below describes the elements of a PLC briey:
Fig.1-1 Processing Architecture of PLC
Various loads
Human-Machine Interface,
SCADA, other PLC,
Inverter, Thermostat, .....
Programming tool
Programmable controller
Input interface
Program processing unit
Output interface
Programming
interface
Communication
interface
Program memory
for user program
Data memory
Power
supply
˙˙˙˙˙
Electromagnetic
contactor,
Motor,
Indicator,
Solenoid valve,
˙˙˙˙˙
Power supply Inside of a PLC consists of ordinary electronic circuit that must use low voltage DC power.
Currently, a PLC manufacturer provides with the AC or DC power input model for the customer to choose from.
The AC power model has a power supply circuit within the PLC to convert AC to DC. The DC power model needs to
provide its power from an external DC source (usually DC 24V) then the PLC uses the internal DC to DC circuit to
convert the power to supply the internal circuit require.
Program processing unit The CPU is the core of a PLC, that is responsible for interpreting the user programs
and calculating the results to achieve the purpose of control.
1
1. Introduction of VS series PLC
1-1 The Basic Concept of PLC Users
1-1-1 Introduction of PLC
The programmable Logic Controller (PLC) is an industrial computer control system that is easy to maintain, low cost
and saves space. In addition to its programmable features, because it is used in the eld of industrial control, PLC is
also required to have high reliability and resistance to climate.
The concept of PLC was introduced by General Motors in 1968. It has been developed by decades. The initial PLC only
had the simple logic control ability, and thus was named as a programmable logic controller. Since Today's PLC
functions have covered the scopes of mathematical operations, servo control and communication links, the more
correct name for it should be programmable controller (referred to as PC), which means a controller that is
programmable. Due to the fact that it shares the same English abbreviation with the personal computer (referred to as
PC). Therefore, in order to distinguish, the programmable controller is referred to as PLC.
PLC has micro controller at its core. The rapid development of semiconductor technology has substantially increased
PLC's computing speed, program capacity and communication connectivity and decreased its prices. Coupled with the
demands on high reliability and resistance to climate the design requirements, PLC is widely used in the eld of
automatic control, and has become an extremely important part.
1-1-2 Configuration of PLC
Various input components
Peripheral equipment
Handheld programming
device or
PC programming software
This is because the use of external DC power supply can avoid the event of unstable AC power input to damage the
controller (this problem is easy to handle if an external DC power supply is used);This is because the use of external
DC power supply can avoid the event of unstable AC power input to damage the controller (this problem is easy to
handle if an external DC power supply is used); therefore, the use of external power supply increases the stability of
control systems. On the other hand, it lowers the general cost of control systems. It is to kill two birds with one stone.
Small PLCs usually use microcontrollers as the core. Now the semiconductor technology has been able to integrate
CPU, memory and a variety of peripheral circuits into a SOC (System On Chip). This not only improves the overall
performance, but also reduces costs. So now, even small PLCs use high-performance 32-bit CPU chip to produce
controllers with fast execution, large program capacity and diverse functions, the real value for money.
Limit switch,
Proximity switch,
Photoelectric switch,
Button switch,
In the past, user prefers to use the AC power input models. However, since there are many related equipments
inside the control panel also required DC power, the use of an external DC power supply to provide all DC
consumptions is popular in recent years.
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