Siemens OP177BPN/DP panel

Siemens OP177BPN/DP panel Siemens OP177BPN/DP panel

Xunzhiman Intelligent Control Technology (Shanghai) Co., Ltd. Shanghai Shimu Automation Equipment Co., Ltd

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1. One of the PROFIBUS DP systems: master/slave system with DP port

The master/slave system design with DP port is very flexible, allowing different data areas in the CPU to store DP process data. The selection of data regions depends on the type and application of CPU. The process image area, bit memory, and data blocks can all be used for DP input and output data.

Process mapping is a standard data allocation. There must be sufficient space in the process image of the CPU to reserve a continuous input area and a continuous output area for DP. This may be limited by the size of the process image and the number of signal modules in the central configuration.

The bit memory is the same as the process image, and this area is suitable for global storage of DP signals. For example, if the available space for process mapping (space not occupied by the central signal module) is insufficient, a bit storage area can be used.

Data blocks can also be used to store DP signals. This type of storage is only used when the DP data area is called by one program.

Establish the hardware configuration of S7-300 PLC master station (with DP port): Double click on the "X2/DP" column or "CP342-5" column, and select "DP Master" in the dialog box

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Order number: 7MH4950-1AA01
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Monitoring of material level in the hopper bin.

Crane and wire rope loads, other tension measurements.

Load measurement for industrial elevators and steel mills

Weighing in hazardous explosive areas (with SIWAREX IS explosion-proof interface)

PLC concept for measuring belt tension
1. Basic concepts of PLC
A programmable controller is a member of the computer family designed and manufactured for industrial control applications. Early programmable controllers were called Programmable Logic Controllers (PLCs), which were mainly used to replace relays for logic control. With the development of technology, the functions of this device have greatly exceeded the scope of logic control. Therefore, today this device is called a programmable controller, abbreviated as PC. However, in order to avoid confusion with the abbreviation of personal computer, the programmable controller is abbreviated as PLC
2. Basic structure of PLC
PLC is essentially a computer for industrial control, and its hardware structure is basically the same as that of a microcomputer, as shown in the figure:
a. Central Processing Unit (CPU)
The central processing unit (CPU) is the control center of the PLC. It receives and stores user programs and data entered from the programmer according to the functions assigned by the PLC system program; Check the status of power supply, memory, I/O, and alert timer, and be able to diagnose syntax errors in user programs. When the PLC is put into operation, it first receives the status and data of various input devices on site in a scanning manner, and stores them separately in the I/O mapping area. Then, it reads the user program from the user program memory one by one, interprets the commands, and executes logical or arithmetic operations according to the instructions. The results are then sent to the I/O mapping area or data register. After all user programs have been executed, transfer the output states of the I/O mapping area or the data in the output registers to the corresponding output devices, and repeat this process until it stops running.
In order to further improve the reliability of PLCs, in recent years, redundant systems with dual CPUs or voting systems with three CPUs have been adopted for large PLCs. In this way, even if a CPU fails, the entire system can still operate normally.
b、 memory
The memory that stores system software is called system program memory.
The memory that stores application software is called user program memory.
C、 Power supply
The power supply of PLC plays a very important role in the entire system. Without a good and reliable power system, it cannot function properly, so PLC manufacturers attach great importance to the design and manufacturing of power supplies. Generally, if the AC voltage fluctuates within the range of+10% (+15%), the PLC can be directly connected to the AC power grid without taking any other measures.
3. The working principle of PLC
One Scanning technology
After the PLC is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution, and output refresh. Completing the above three stages is called a scanning cycle. During the entire operation, the CPU of the PLC repeatedly executes the above three stages at a certain scanning speed.
（1） Input sampling stage
In the input sampling stage, the PLC sequentially reads in all input states and data in a scanning manner, and stores them in the corresponding units in the I/O mapping area. After the input sampling is completed, it enters the user program execution and output refresh phase. In these two stages, even if the input state and data change, the state and data of the corresponding unit in the I/O mapping area will not change. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scanning period to ensure that the input can be read in under any circumstances.
（2） User program execution phase
During the execution phase of the user program, the PLC always scans the user program in a top-down order (ladder diagram). When scanning each ladder diagram, always scan the control circuit composed of each contact on the left side of the ladder diagram first, and perform logical operations on the control circuit composed of contacts in the order of left to right and top to bottom. Then, based on the result of the logical operation, refresh the corresponding bit status of the logical coil in the system RAM storage area; Or refresh the status of the corresponding bit of the output coil in the I/O mapping area; Or determine whether to execute the special functional instructions specified in the ladder diagram.
That is, during the execution of the user program, only the state and data of the input point in the I/O mapping area will not change, while the state and data of other output points and software devices in the I/O mapping area or system RAM storage area may change. Moreover, the ladder diagram at the top will have an effect on any ladder diagram below that uses these coils or data; On the contrary, in the ladder diagram below, the status or data of the refreshed logic coil can only affect the program above it in the next scanning cycle.
（3） Output refresh phase
After scanning the user program, the PLC enters the output refresh phase. During this period, the CPU refreshes all output latch circuits according to the corresponding states and data in the I/O image area, and then drives the corresponding peripherals through the output circuits. At this point, it is the true output of the PLC.
Compare the similarities and differences between the two programs:
Program 1:
Program 2:
The results of these two programs are the same, but the processes executed in the PLC are different.
Program 1 can refresh% M4 with only one scanning cycle;
Program 2 requires four scanning cycles to complete the refresh of% M4.
These two examples illustrate that the same number of ladder diagrams, with different arrangement orders, result in different execution outcomes. In addition, it can also be seen that there is a difference between the running results of scanning user programs and the hard logic parallel running results of relay control devices. Of course, if the time occupied by the scanning cycle can be ignored for the entire operation, then there is no difference between the two.
Generally speaking, the scanning cycle of PLC includes self diagnosis, communication, etc., as shown in the following figure, that is, one scanning cycle is equal to the sum of all the time for self diagnosis, communication, input sampling, user program execution, output refresh, etc.
II I/O response time of PLC
In order to enhance the anti-interference ability of PLC and improve its reliability, each switch input terminal of PLC adopts technologies such as photoelectric isolation.
In order to achieve hard logic parallel control of relay control circuits, PLC adopts a different operating mode from general microcomputers (scanning technology).
The above two main reasons make the I/O response of PLC much more full than that of industrial control systems composed of general microcomputers, and its response time is at least equal to one scanning cycle, generally greater than one scanning cycle or even longer.
The so-called I/O response time refers to the time required from the change of a certain input signal of the PLC to the change of the relevant output signal of the system. The short I/O response time and long I/O response time are shown in the figure:
The (n-1) th one
scanning cycle
Short I/O response time:
Long I/O response time
SIEMENS PLC products in China are mainly divided into three types based on their scale and performance: S7-200, S7-300, and S7-400. Below are some characteristics of these three products.
S7-200
For modular small control systems with low performance requirements, it can have the ability to expand up to 7 modules and integrate a backplane bus in each module. Its network connections include RS-485 communication interface and Profibus, and all modules can be accessed through a programmer PG. It is an integrated unit device with power supply, CPU, and I/O.
There are several extension modules (EM) among them: Digital Input Module (DI) -24VDC and 120/230VAC; Digital output (DO) -24VDC and relay; Analog input module (AI) - voltage, current, resistance, and thermocouple; Analog output module - voltage and current. There is also a relatively special module - the Communication Processor (CP) - whose function is to connect the S7-200 as the master station to the AS interface (sensor and actuator interface). Through the AS interface, the slave station can control up to 248 devices, significantly expanding the input and output points of the S7-200.

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*Spot supply of Siemens weighing modules
　
siemens 7MH4930-0AA01
　
siemens 7MH4950-1AA01
　
siemens 7MH4950-2AA01
　
siemens 7MH4900-2AA01
　
siemens 7MH4900-3AA01

　
Another good discount to order the following products
　
siemens 7MH42/45/49/47/31/41/51/57
　
siemens 7MH7122/7123/7121/7125/7126
　
siemens 7MH7130/7134/7131/7132/7176
　
siemens 7MH717/7170/7150/7152/7156/710/711
　
siemens 7MH77/ 7MH7560/ 7MH7562/7146/7144/7142/7145

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Design Method of Programmable Logic Controller Control System

1、 Question raised

Programmable controller technology is mainly applied in automation control engineering. How to comprehensively apply the knowledge points learned earlier and combine them reasonably according to actual engineering requirements to form a control system? Here is an introduction to the general method of forming a programmable controller control system.

2、 Basic steps of programmable controller control system design

1. Main content of system design

(1) Develop technical specifications for the design of the control system. Technical conditions are generally determined in the form of a design task book, which serves as the basis for the entire design;

(2) Choose the form of electrical transmission and actuators such as electric motors and solenoid valves;

(3) Select the model of PLC;

(4) Prepare input/output allocation table for PLC or draw input/output terminal wiring diagram;

(5) Write software specifications according to the requirements of system design, and then use the corresponding programming language (commonly ladder diagram) for program design;

(6) Understand and follow user cognitive psychology, value the design of human-machine interfaces, and enhance the friendly relationship between humans and machines;

(7) Design workstations, electrical cabinets, and non-standard electrical components;

(8) Write design specifications and user manuals;

According to specific tasks, the above content can be adjusted appropriately.

2. Basic steps of system design

The main steps of designing and debugging a programmable controller application system are shown in Figure 1.