Tag Archives: PLC control system

How Siemens S7-200 series PLC’s power requirements and calculation?

S7-200 CPU module provides 5VDC and 24VDC power supply:
When an expansion module CPU through I / O bus to provide 5V power supply, all the expansion module 5V power consumption of the CPU and can not exceed the rated power provided. If not enough external 5V power supply. Each CPU has a 24VDC sensor power supply, it is native input and expansion module input and expansion modules provide relay coil 24VDC.
If the power requirement exceeds the power budget of the CPU module, you can add an external 24VDC power supply to provide to the expansion module.
The so-called power calculation is to use the CPU can provide power capacity, minus the modules required to power consumption.
Note: EM277 module itself does not require 24VDC power supply, the power supply is designed for communication port used. 24VDC power supply requirements depend on the size of the load on the communication ports.
Communication port on the CPU, you can connect PC / PPI cable and TD 200 and give them power, the power consumption has no longer included in the calculation.

Three types of Siemens industrial control software introduction

Siemens industrial software is divided into three different categories:
(1) programming and engineering tool for programming and engineering tool includes all PLC-based or PC for programming, configuration, simulation and control tools needed maintenance. STEP 7 standard package SIMATIC S7 for S7-300 / 400, C7 PLC and SIMATIC WinAC PC-based control product configuration programming and maintenance of project management tools, STEP 7-Micro / WIN is running on a Windows platform S7 -200 series PLC programming, on-line simulation software.
(2) PC-based control software WinAC PC-based control systems allow the use of a personal computer as a programmable logic controller (PLC) run user programs run in Windows NT4.0 operating system installed on the SIMATIC IPC or any other commercial machine. WinAC offers two PLC, one is software PLC, on the user’s computer to run as a Windows task. Another is the slot PLC (install a PC card in the user’s computer), it has all the features of the hardware PLC. WinAC and SIMATIC S7 series processor is fully compatible with its unified programming SIMATIC programming tools (eg STEP 7), programmed to run on either WinAC, also runs on S7 series processors.
(3) human-machine interface software HMI automation software for users to project human-machine interface (HMI) or SCADA system that supports a wide range of platforms. HMI software, there are two, one is applied to the machine-level ProTool, the other is applied to monitor the level of WinCC.
ProTool for most HMI hardware configuration from the operator panel to a standard PC can be used to integrate effectively complete the configuration of ProTool in STEP 7. Configuring ProTool / lite for text display, such as: OP3, OP7, OP17, TD17 like. ProTool / Pro is used to configure all the standard PC and Siemens HMI products, ProTool / Pro not only configuration software, which runs Windows version is also used to monitor system platform.
WinCC is a truly open-oriented monitoring and data acquisition SCADA (Supervisory Control and Data Acquisition) software can be run on any standard PC. WinCC simple operation, high reliability, integration with STEP 7 function, direct access to the PLC system hardware failure, save project development time. It is designed for a wide range of applications, can be connected to the existing automation environment, a large number of communication interfaces and comprehensive process information and data processing capabilities, its latest WinCC5.0 support via IE browser dynamic monitoring of production at the office process

To simplify and write PLC ladder command statement table ladder program

After simplifying the ladder

Instruction Statement List
a) LD        01600
AND       00002
LD-NOT    00001
AND       00000
OUT       10000
b)LD-NOT    00004
AND       00005
LD         10000
AND       00006
AND       00003
LD         00002
AND       00004
AND       00001
OUT       10000
c)LD         10000
AND       00003
AND       00004
OR         00001
AND       00000
LD         10000
AND       00001
LD         00003
AND       00004
AND       00002
OUT       10000

SIEMENS S7-300 PLC CPU module component

S7-300 there are many different types of CPU, suitable for different levels of control. CPU module is integrated with the digital I/O, and integrated digital I/O and analog I/O.

CPU component is packaged in a sturdy and compact plastic enclosure, Panel on the status and error indicator LED, mode selection switch and communication interfaces. Micro memory card slot you can insert up to several megabytes of FEPROM micro memory card (MMC), after loss of program and data preservation. Some CPU, only one MPI interface.

1. Status and fault indication LED

CPU module Panel for LED (light emitting diode) the meaning of

CPU in RUN mode RUN LED lit; 2Hz frequency during boot shining; HOLD State with 0.5Hz frequency lights. When CPU is STOP, HOLD or restart STOP LED Permanent; request a memory reset to 0. 5Hz frequency blinking are the memory reset to 2Hz frequency lights.

2. CPU operation mode

1) STOP (stop) mode: the mode selector switch is in the STOP position, automatically enters STOP mode after power on the CPU module, which does not execute user program can receive global data and checking the system.

2) RUN (run) mode: execute user programs, refresh the input and output, handling interrupts and faults information services.

3) HOLD mode: start and RUN mode when debugging with breakpoints, the user program execution is suspended (paused), the timer is frozen.

4) STARTUP (boot) model: you can use the mode selector switch or STEP 7 start the CPU. If the mode select switch is in the RUN position, power on automatically when entering the start mode.

5) old CPU key to switch to select the operation mode, it also has a RUN-P mode, allows to read and modify the program at runtime. Simulation software simulation of the PLCSIM CPU RUN-P mode, certain monitoring functions can only be carried out in RUN-P mode.

3. Mode selector switch

CPU mode selector switch to the position of significance are as follows:

1) RUN (run): CPU execute user programs.

2) STOP (stop): CPU not execute user programs.

3) MRES (memory reset): MRES position cannot be maintained in this position when you let go the switch will automatically return to the STOP position. From the STOP position to pull the mode selection switch into the MRES position, can reset the memory, the CPU back to the initial state. Working memory and S7-400 of RAM loaded in memory user program and address area is cleared, all memory, timers, counters and data block is reset to zero, including the data hold function. CPU hardware, initializing the hardware and system parameters, system parameters, CPU and is restored to the default settings of the parameters of the module, MPI (multi point interface) parameter is reserved. CPU inside the MMC after the reset of the user programs and system parameters are copied to the storage area.

Reset memory operations in the following order: PLC power from the STOP position to pull the mode selection switch into the MRES position, STOP LED extinguished 1s, 1s, went out again after 1s remain on. Release the switch and make it return to the STOP position. 3S to pull to the MRES position, STOP the frequency flashing at least 3s LED 2Hz, said it is a reset, finally STOP LED on, reset the end, you can release the mode selector switch.

4. Communication interface

All CPU modules have a MPI (multi point interface) communication interfaces, some CPU module with PROFIBUS-DP interface or a point to point interface, model PN CPU modules in an industrial Ethernet PROFINET interfaces.

MPI interface is used with other Siemens PLC, PG/PC (programmer or a PC), OP (operator panel) through the MPI network communications.

PROFIBUS-DP can be used with other Siemens PLC, PG/PC, OP and other DP master and slave communications.

5. Power terminal blocks

The power supply module L+ and m terminals DC 24V output voltage anode and cathode, respectively. Use dedicated power connector or wires connected to the power supply module and the L+ CPU module, and m terminals.

The difference between Simens PLC programming FB and FC

FB–function blocks, blocks with background data
FC–function, or function
They Zhijian of main difference is: FC using of is shared data block, FB using of is background data block lift a example, if you to on 3 a parameter same of motor for control, so only need using FB programming plus 3 a background data block on can has, but, if you using FC, so you need constantly of modified shared data block, or will led to data lost. FB 3 motor parameters are ensuring noninterference.

FB,FC of the essence is the same, are equivalent to the subroutine can be called by another program (you can also call other subroutines). The biggest difference between them is that FB for use with DB, DB holds FB data, even if FB after the withdrawal will remain. FC does not have a data block to store the data permanently, will be assigned a temporary data at run time. In actual programming, are using FB or FC, depends on the actual needs. FB benefits upstairs to very well.

No much difference between FB and FC, FB with a background chunk, FC did not. FB data with different blocks, you can take different parameter values. So you can use the same FB and various background chunks, called by more than one object.

FC and FB like c functions, though FB can generate static variables, data will be saved in the next function call, and FC variable is only valid during the call period, the next call to replace.

S7-300plc FB and FC respectively? FB has its own background, DB and DB FC does not have its own background, FC and FB have a difference, they can achieve the control function, what to use FB or FC should be used, when using FB when FC?
No much difference between FB and FC, FB with a background chunk, FC did not. FB data with different blocks, you can take different parameter values. So you can use the same FB and various background chunks, called by more than one object.

FC and FB like c functions, though FB can generate static variables, data will be saved in the next function call, and FC variable is only valid during the call period, the next call to replace. Each call to the FC I/O areas must be of yourself each time you manually enter, and FB is not, save a lot of trouble, if the PC can control directly to the DB control address.

FX3U PLC external sensor connection

PLC FX3U some columns may be NPN type or PNP type sensor and wiring simple.

FX3U S/S on terminals, S/S by Terminal block of 24V and 0V terminals or terminal connected to leak, source input switch.

Missing input: connect the 24V and S/S terminals

Source input: connect the 0V terminals and S/S Terminal

By choosing you can set the basic unit of input enter input or source for the leak, but not mixed.

Basic unit and input/output expansion unit you can select leakage input or source input.

Design of PLC control system the main steps to be followed and the content

(1) technical analysis
In-depth understanding of process control object, features, requirements, and dividing control of all phases, summarized the various stages of, and between the various stages of transition conditions, draw the flowchart control flow chart or function.
(2) select the appropriate PLC type
When you select the PLC model, mainly consider the following points:
 1 choice of functions. For small PLC main I/O expansion module, a/d and d/a modules and features of the directive (such as interrupt, PID, etc).
 2 I/O number to determine. Statistical control system switches, analog I/O point numbers, and consider future expansion (General plus 10%~20% spare capacity), to choose the PLC I/O points and output specifications.
 3 memory estimate. User program memory required is mainly with the system‘s I/O points and control requirements, length of program structure and other factors. General estimation according to the following formula: storage capacity = switch input points x8+ points X10+ switch output analog channel number x100+ number x300+ number X2+ communications interface standby timer/counter.
(3) allocation of I/O points. Distribution PLC input/output points, write input/output allocation table or input/output terminals the wiring diagram, and PLC programming, both control cabinet or console design and field construction.
(4) program. For more complex control systems, according to the production requirements, draw the flowchart control flow chart or function, and then design a ladder diagram, again according to the prepared statement form the ladder program, staging and modifications to the program, up until the requirement is met.
(5) the controller or console design and field construction. Designing control cabinets and work station layout and installation of electric wiring diagram; design components of the control system of the electrical interlock diagram according to drawings for field wiring and check.
(6) using the integrated debugging. If the control system consists of several components, you should first make a local debugging, and make the whole debugging; more if you control the sequence, the segment can be debugged, and then dispatching and connected.
(7) prepare technical documents. Technical papers should include: programmable controllers wiring diagram electrical engineering, electrical layout, electrical component breakdown, sequential function chart, ladder diagram with notes and descriptions.

Design of PLC control system and debug steps

(A) analysis of controlled objects control requirements and

Detailed analysis of control processes and characteristics about control of interaction between mechanical, electrical, fluid, made the control requires control of PLC control system, identification of programmes, development proposal.

(B) determine the input/output devices

According to the system requirements, and determine all of the required input devices (such as push button, position switches, switches and sensors, and so on) and output devices (such as contactors, solenoid valves, signal lights, and other devices, and so on) to determine the associated with the PLC input/output devices, to determine the PLC I/O points.

(C) select PLC

PLC selection including the PLC model, capacity, I/O modules, power supplies and other options, as described in section II of this chapter.

(D) allocation of design PLC I/O and peripheral hardware lines

1. allocation of I/O points

Draw the PLC I/O points corresponding to the connection diagram input/output devices, or relational tables, which can be carried out in the 2nd step.

2. PLC peripheral hardware circuit design

Draw the electrical wiring diagram for other parts of the system, including the main circuit and do not enter the PLC control circuit and so on.

By the PLC I/O connection diagrams and PLC peripheral electrical wiring diagram the electrical schematics of the system. End system hardware circuit has been identified.

(E) programming

1. program design

According to the system requirements, using appropriate design methods to design the PLC program. Procedures to control to meet the system requirements as the main line, write the control functions or tasks one by one program, gradually improved the system to the specified function. In addition, programs should also include the following:

1) initialization program. PLC poweron, are generally required to do some initialization operations, to start the necessary preparations to avoid malfunction of the system. Initializes the main elements of the program are: to clear certain data, counters and other, to restore some data requirements data, to set or reset certain relays, to display certain initial state, and so on.

2) detection and trouble diagnosis and display program. These programs are relatively independent, generally when the program is completed, adding.

3) protection and linkage programs. Protection and chain are indispensable parts of the program, must be seriously considered. It can avoid the control logic confused due to illegal actions.

2. program debugging

Program the basic idea of staging is to facilitate simulations in the form of actual state, to run programs to create the necessary conditions. According to the signal in different ways, staging a hardware simulation and software simulations in two forms.

1) hardware simulation method is to use a hardware device (such as a PLC or other input device, and so on) simulate signals, and these signals to hard wire connected to the input of the PLC system, its effectiveness is stronger.

2) software in PLC, the modeling method is writing a simulation program, analog provide local signals, its simple, but time is not easy to ensure. In the staging process, methods that can be used to debug and program monitoring function.

(F) the hardware implementation

Hardware implementation is mainly to control cabinet (set), such as hardware design and field construction. Main content:

1) designing control cabinets and floor plan and console and other parts of the electrical installation wiring diagram.

2) design the electrical interconnection between the different parts of the system.

3) according to the construction drawings for field wiring, and to conduct an examination.

Due to programming and hardware implementation may simultaneously carry on, so can shorten the design cycle of PLC control system.

(G) debugging

Debugging is to further online tracking through the staging process. Debugging process should be gradual, from the PLC connected input device, and then connect the output device, and then connect to the actual load step by step debugging. If you do not meet the requirements, then adjust hardware and programs. Often only part of the program.

After the full commissioning, delivery operation. After a period of time, if working properly, the program does not need to be modified, procedures should be cured in the EPROM, in case the program is missing.

(H) the collation and preparation of technical documents

Technical documentation including design specifications, hardware schematics, wiring diagrams, electrical components, PLC program, and use the schedule description

Design of PLC control system of the four cardinal principles

1 meet control requirements of the controlled object.
2 in the premise of meeting the requirements to make simple, affordable, easy to use and maintenance of control system.
3 ensure that the control system is safe and reliable.
4 taking into account the development of the production and improvement of technology in select PLC capacity should be appropriate enough.

PLC control system design of the basic principles and main contents

1. design principles
In order to achieve controlled technology to improve production efficiency and product quality.
1. selection of PLC should not only meet the requirements of specification, you should also focus on technical support and after-sales service of the company‘s products. (Choose product)
2. to meet the control requirements of the controlled object.
3. meet the requirements of the premise, sought to make the control system is simple, economical, convenient operation and maintenance.
4. ensure the control system is safe and reliable.
5. taking into account the development of the production and process improvement, select PLC capacity should be adequate enough.
2. the design of the main content
1. preparation of technical conditions for design of the control system. General technical conditions to determine as a design task, it is the Foundation of the entire design;
2. Select electric drives and motors, solenoid valves, actuators;
3. the model of the selected PLC;
4. development of PLC input/output assign table drawing input/output terminals or wiring diagram;
5. prepared software specifications according to the system design, and then use the corresponding programming languages (ladder diagram) programming;
6. understand and follow the user‘s cognitive psychology, emphasis on human-machine interface design and enhance friendly relationship between man and machine;
7. design work, electrical cabinets and non-standard electrical components;
8. the preparation of design specifications and instructions;