Siemens Taizhou authorized agent

Siemens Taizhou authorized agent Siemens Taizhou authorized agent

SIEMENS Xunzhiman Intelligent Control Technology (Shanghai) Co., Ltd

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The operational functions of a simple PLC include logical operations, timing, and counting functions; The general operation functions of PLC also include data shifting, comparison and other operation functions; More complex computational functions include algebraic operations, data transmission, etc; In large PLCs, there are also analog PID operations and other advanced computing functions. With the emergence of open systems, PLCs now have communication functions. Some products have communication with lower level computers, some products have communication with same level or upper level computers, and some products also have data communication functions with factory or enterprise networks. When planning and selecting, one should start from the requirements of practical application and reasonably choose the required computational functions. In most applications, only logical operations and timing counting functions are required. Some applications require data transmission and comparison. When used for analog quantity detection and control, algebraic operations, numerical conversion, and PID operations are used. To display data, decoding and encoding operations are required.

（2） Control function

The control functions include PID control operation, feedforward compensation control operation, ratio control operation, etc., which should be determined according to the control requirements. PLC is primarily used for sequential logic control. Therefore, in most cases, single loop or multi loop controllers are often used to solve analog control. Sometimes, intelligent input and output units are also used to complete the required control functions, improve the processing speed of PLC, and save memory capacity. For example, using PID control units, high-speed counters, imitation units with speed compensation, ASC code conversion units, etc.

（3） Communication function

Large and medium-sized PLC systems should support multiple fieldbus and standardized communication protocols (such as TCP/IP), and should be able to connect with the factory management network (TCP/IP) when required. The communication protocol should comply with ISO/IEEE communication standards and be an open communication network.

（4） Programming function

Offline programming method: PLC and programmer share a CPU. When the programmer is in programming mode, the CPU only serves the programmer and does not control the on-site equipment. After completing the programming, the programmer switches to the operating mode, and the CPU controls the on-site equipment and cannot perform programming. Offline programming methods can reduce system costs, but they are inconvenient to use and debug. Online programming method: The CPU and programmer have their own CPUs. The host CPU is responsible for on-site control and exchanges data with the programmer during a scanning cycle. The programmer sends the online program or data to the host, and in the next scanning cycle, the host runs according to the newly received program. This method has a high cost, but is easy to debug and operate, and is often used in large and medium-sized PLCs.

Five standardized programming languages: Sequential Function Diagram (SFC), Ladder Diagram (LD), Functional Block Diagram (FBD), three graphical languages, and Sentence List (IL) and Structured Text (ST), two textual languages. The selected programming language should comply with its specifications (IEC6113123), and should also support multiple language programming forms, such as C, Basic, etc., to meet the control requirements of special control situations.
What are the reasons for PLC analog input interference
PLC functional module
I believe many friends who work in automation have encountered the phenomenon that if there is no problem with collecting analog signals on site, the PLC may not operate normally. Even if grounding and shielding are done well, it is still a drop in the bucket. There is nothing we can do to solve these problems. Today, I will share with you some causes and solutions for on-site interference.
1. Strong electrical interference
The meter signal and PLC control signal are both weak current and susceptible to strong electrical interference. So it is required that when wiring outside the cabinet (in cable trenches, cable trays, conduits, etc.), weak current signals such as communication lines, signal lines, and control lines should be kept away from strong current, with a spacing of not less than 20cm. When the cable trench is multi-layered, weak current cables should be laid below strong current cables.
2. Interference inside the cabinet

PLC cannot be installed in the same switchgear as high-voltage electrical appliances. The output of PLC uses a central relay to block external switch signals. If the on-site conditions are constrained and the input signal cannot be effectively blocked by the strong current cable, a small relay can be used to block the switch signal at the input end. Of course, it is generally not necessary to use relays to block the input signals from the PLC control cabinet and the input signals not far from the control cabinet. When wiring the PLC, the negative terminal of the analog input module should be short circuited as much as possible to eliminate interference.

3. Anti interference of signal lines
The interference of signal lines mainly comes from electromagnetic radiation in space, including differential mode interference and common mode interference. Differential mode interference refers to the interference signal superimposed on the measurement signal line, which is mostly a high-frequency alternating signal, and its origin is generally coupling interference. The methods to suppress normal interference include:
Connect an RC filter or a double-T filter to the input circuit; Try to choose a double integral fraction A/D converter as it has the characteristic of eliminating high-frequency interference due to the operation of this integrator; Convert the voltage signal into a current signal and transmit it.
Common mode interference refers to the interference signal shared on the signal line, usually caused by a certain potential difference between the ground terminal of the measured signal and the ground terminal of the control system. When the period and amplitude of this interference are basically equal on the two signal lines, the above methods cannot eliminate or suppress it. The method is as follows:
Choose a differential amplifier with dual differential inputs, which has a high common mode rejection ratio;
The input line is made of twisted wire, which can reduce common mode interference and cancel each other's induction;
The use of photoelectric blocking method can eliminate common mode interference;