Introduction of Siemens PLC


Siemens makes several PLC product lines in the SIMATIC S7 family. They are: S7-200, S7-300, and S7-400. Siemens Step 7 is a powerful integrated software solution for automation, and includes the programming environment for Siemens programmable logic controllers (PLCs). This software provides unique and powerful programming tools with multiple benefits including: creation of re-useable logic, a structured program architecture, and single project integration of multiple automation devices.

Do you want to know more about Allen Bradley PLC

Types of Siemens PLC

Compact:-  I/O number fixed.

Modular :-  I/O can be as per selection.

Types of PLC

S5-STEP5   –   DOS base system.

S7-STEP7   –  WINDOWS base system.

STEP-7 Groups

(STEP – Siemens Technical Education Program)

1) S7 200 :-

Compact Type PLC.

Use for small scale industry.

CPU Available – CPU 212 to CPU 226.

Digital I/O Capacity – 256.

Analog I/O Capacity- 38.

Programming software – micro win.

Communication Driver – PPI (Point to Point interface).

2) S7 300 :-

Compact and Modular type PLC

Use for Small and Medium Scale industry.

CPU Available – CPU 312 to CPU 318.

Digital I/O Capacity – 1024.

Analog I/O Capacity- 256

Programming software – Simatic Manager.

3) S7 400 :-

Modular Type PLC.

 Use for Large Scale industry.

DP Port Available.

CPU Available – CPU 412 to CPU 418.

Digital I/O Capacity – 16384.

Analog I/O Capacity- 4000.

Programming software – Simatic Manager.

Siemens PLC Hardware

PS  : – Power Supply.

CPU:- Central Processing Unit.

IM:- Interface Module.

SM:- Signal Module(I/O modules).

Bus Connector Rack (rail): – Eleven slot rail.

CP:- Communication Processors.

FM:- Function Module.

IM – Interface Module:-

Interface Module use to connect or interface one rack to another rack.

SM – Signal Module (I/O modules):-

Simple  Input/output can be Interfaced with through Signal Module.

CP – Communication Processors:-

Communication Processor used in Networking Communication Between many processors or plc.

FM – Function Module:-

Special Purpose controlled like PID, CNC, position controller, Cam controller can be interfaced to PLC through FM cards.

CPU memory Organization

CPU memory divided in blocks:-

OB -Organization Block(OB1-main block)

FC -Functions(Subroutine -user defined)

FB -Functional Block(defining function)

DB  -Data Block(creating memory data)

Types of CPU Memory:-

Load memory:- User program stored, capacity can be changed by MMC up to 256k.

Work memory:-Instructions required program execution.

System memory:-Timer, Counter, memory bits, Process Image Memory, buffer diagnostics.

Communication Protocols :-

1) RS232 :-  Bound rate 19,200 bits/sec. maximum length 10m. connector nine pin delta.

2)DH485:- Data Highway,32node components, bus rate 19,200 bit/sec. Maximum length 4000 feet (1.2 km) connector RJ 45 (radio jack).

3)MPI :- multi Point interface bound rate 1.5 mbps default,187.5 kbps, no of maximum nodes 32, network length 4000 ft, MPI use  for PLC programming, inter CPU Communication, Scada/HMI communication.

4) Profibus:- Process field bus, Bound Rate 12 mbps, no of maximum nodes 126, network length 4000 ft, Profibus also used for remote I/Os and drives Communication.


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