2. Interference in the control system and its sources
On-site electromagnetic interference is one of the most common factors in PLC control system and most likely to affect the reliability of the system. Therefore, it is important to know the source of the interference in the field.
(1) Interference sources and general classification
Most of the interference sources affecting the PLC control system are generated in the parts where the current or voltage changes drastically, and the reason is that the current changes to produce a magnetic field and electromagnetic radiation to the equipment; The change in the magnetic field produces an electric current, and the electromagnetic wave is generated by the electromagnetic wave at high speed. Generally, electromagnetic interference is divided into common-mode interference and differential-mode interference according to different interference modes. Common-mode interference is the potential difference between the signal and the ground, which is mainly formed by the superposition of the common (in the same direction) voltage induced by the power grid series, the ground potential difference and space electromagnetic radiation on the signal line. The common-mode voltage can be converted into a differential-mode voltage through the asymmetric circuit, which directly affects the measurement and control signal and causes damage to the components (which is the main reason for the high damage rate of some system I/O modules), and this common-mode interference can be DC or AC. Differential mode interference refers to the interference voltage acting between the two poles of the signal, which is mainly formed by the coupling induction between the signals by the space electromagnetic field and the conversion of common mode interference by the unbalanced circuit, which is superimposed on the signal and directly affects the measurement and control accuracy.
(2) The main sources and ways of interference in the PLC system
Strong electrical interference
The normal power supply of the PLC system is powered by the power grid. Due to the wide coverage of the grid, it will be subject to all space electromagnetic interference to induce voltages on the line. In particular, the changes within the power grid, such as the surge of knife switch operation, the start and stop of large power equipment, the harmonics caused by AC and DC transmission devices, and the transient impact of short circuit of the power grid, are transmitted to the primary side of the power supply through the transmission line.
Interference in the cabinet
The high-voltage electrical appliances in the control cabinet, large inductive loads, and chaotic wiring are easy to cause a certain degree of interference to the PLC.
Interference introduced from signal lines
In addition to transmitting all kinds of effective information, there will always be external interference signals intrusion in all kinds of signal transmission lines connected to the PLC control system. There are two main ways of this interference: one is the grid interference connected through the power supply of the transmitter or the power supply of the shared signal instrument, which is often overlooked; Second, the signal line is interfered by space electromagnetic radiation induction, that is, the external inductive interference on the signal line, which is very serious. The interference introduced by the signal will cause the I/O signal to work abnormally and the measurement accuracy will be greatly reduced, and in severe cases, it will cause component damage.
Interference from the time of chaos in the grounding system
Grounding is one of the effective means to improve the electromagnetic compatibility (EMC) of electronic equipment. Correct grounding can not only suppress the influence of electromagnetic interference, but also suppress the interference of the equipment to the outside; Wrong grounding, on the contrary, will introduce serious interference signals, so that the PLC system will not work properly.
Interference from within the PLC system
It is mainly generated by the mutual electromagnetic radiation between the internal components and circuits of the system, such as the mutual radiation of logic circuits and their influence on analog circuits, the interaction between analog and logical grounds, and the mutual mismatch between components.
Inverter interference
First, the harmonics generated during the start-up and operation of the inverter will cause conductive interference to the power grid, causing the voltage distortion of the power grid and affecting the power supply quality of the power grid; Second, the output of the inverter will produce strong electromagnetic radiation interference, which will affect the normal operation of peripheral equipment.
|
More on that
|
Hollysys PLC - the characteristics of the working process of PLC
(1) The PLC adopts the working mode of centralized sampling and centralized output, which reduces the influence of external interference.
(2) The working process of PLC is the process of cyclic scanning, and the length of cyclic scanning time depends on the speed of instruction execution, the length of the user program and other factors.
(3) Output ...
|
|
Hollysys DCS - Introduction to the main features of DCS
(1) High reliability
DCS is designed to be fault-tolerant, so that when a computer fails, it does not cause the system to lose other functions. In addition, because the tasks undertaken by the individual computers in the system are relatively simple, it is possible to adopt a specific structure and ...
|
|
The scientific and technological achievements of "SCADA system development and refined oil pipeline application based on independent chips and operating systems" have reached the international advanced level
On October 15, 2022, the scientific and technological achievement of "SCADA system development and refined oil pipeline application based on independent chips and operating systems" jointly completed by South China Branch of National Petroleum Pipeline Network Group Co., Ltd. and Hangzhou Hollysys Automation Co., Ltd. successfully passed the China Petroleum and Chemical Industry Co., Ltd.
|
|
Hollysys HOLLiAS MACS IC helps the localization of large-scale thermal power units
At 15:05 on January 12, 2022, Datang Anhui Luoneng Power Generation Co., Ltd. (hereinafter referred to as Datang Luohe) successfully completed the full-load trial operation of Unit 5 after comprehensive upgrading, marking the smooth operation of Unit 5 of Datang Luohe Power Plant after the transformation. Hollysys HOLLiAS MACS IC completely ...
|
|
Hollysys helped China's first 20,000-ton green electricity to green hydrogen demonstration project be fully put into operation
On August 30, Sinopec announced that China's largest photovoltaic power generation direct production green hydrogen project, Xinjiang Kuqa Green Hydrogen Demonstration Project (hereinafter referred to as the Green Hydrogen Demonstration Project), was fully completed and put into operation, marking a breakthrough in the large-scale industrial application of green hydrogen in China. In this project, and ...
|
|
Hollysys PLC - common causes and treatment methods of PLC failures in operation
1. Peripheral circuit component failure
This type of failure often occurs in the failure of the PLC after a certain period of work. In the PLC control loop, if there is a component damage fault, the PLC control system will immediately and automatically stop working.
The input circuit is a PLC that accepts switching quantities, analog ...
|
|
Hollysys PLC - a component of the PLC control cabinet
1. Open empty
A master air switch that is the power control for the entire cabinet.
2. Power supply
A 24VDC switching power supply.
3、PLC
This should be chosen according to the needs of the project. If the scale of the project is small, the integrated PLC can be used directly; If the item ...
|
|
Hollysys DCS—— Selection, design and debugging of DCS system
1. Configuration of the system and controller
The configuration of systems and controllers focuses on reliability and load factor (including redundancy). The communication load rate must be controlled within a reasonable range, and the load rate of the controller must be balanced as much as possible to avoid the occurrence of "high load" problems.
2 ...
|
|
Century Qualcomm and Hollysys reached a strategic cooperation
With the inclusion of "exploring the construction of digital twin cities" in the 14th Five-Year Plan, the field of intelligent transportation is being endowed with more new business value. Recently, Century Qualcomm and Hollysys reached a strategic cooperation, based on the principle of "giving full play to advantages, mutual promotion, long-term cooperation, mutual benefit and win-win", ...
|
|
Hollysys OCS industrial optical bus control system was successfully applied in Sinopec project
On November 13, 2022, Zhong'an United Coal Chemical Branch came with exciting news that the 20,000 tons/year butene-1 plant produced qualified butene-1 products at 22 o'clock on the same day, and the one-time start-up was successful. The control system of the device adopts the innovative technology product "OCS Industrial Optical Bus Control ...
|
|
Hollysys DCS - DCS fault maintenance measures
Whether it is a new unit or an upgraded DCS, the equipment of the system and controller should focus on the reliability and load factor (including redundancy) objectives. The load rate planning of the communication bus must be controlled within a reasonable range, and the load rate of the controller should be balanced as much as possible.
|
|
and Lisi plc - the difference between DCS and PLC
The choice between a programmable logic controller (PLC) and a distributed control system (DCS) is a case-by-case analysis, as the requirements for the control system vary depending on the application. You can start from the following aspects!
PLC and DCS
PLC
...
|
|
Hollysys DCS - the debugging scheme of DCS system
1. Check before power-on
If the cable insulation resistance meets the requirements (greater than 5M ohms), check the cable insulation resistance test record, and spot check the actual measurement if necessary.
Check that all power cables, signal cables, and communication buses should be connected.
Control stations, operator stations, engineer stations, etc.
|
|
Hollysys assisted Qingdao Petrochemical DCS upgrade
In December 2020, the equipment of Sinopec Qingdao Petrochemical Co., Ltd. (hereinafter referred to as Qingdao Petrochemical) 5 million tons/year oil refining integration project, which was upgraded and transformed by Hollysys, was successfully operated, marking the successful completion of the DCS equipment upgrading task. This upgrade is a major development for Sinopec Industrial Holdings.
|
|
Hollysys PLC - What are the selection methods of PLC?
1. Budget for input and output (I/O) points
When budgeting I/O points, the appropriate margin should be considered, usually based on the calculated number of input and output points, and then add 10%-20% of the expandable, and after the margin, it will be used as the budget data of input and output points. When ordering in practice, it is also necessary to rely on the manufacturer's ...
|
|
Hollysys DCS - Introduction to the hardware architecture of DCS distributed control system
DCS usually adopts a hierarchical and progressive structure, each level is composed of several subsystems, and each subsystem achieves a number of specific finite goals, forming a pyramid structure. Examining the hierarchical structure of DCS, DCS level and control management level are the two most basic links that make up DCS.
Process control...
|
|
Troubleshooting steps of Hollysys DCS system
The steps of DCS system troubleshooting include:
(1) Check the fault caused by improper use.
Common types of operational faults include operator errors, terminal wiring faults, module installation faults, and power supply failures.
(2) Troubleshoot the improper operation of the DCS system ...
|
|
Hollysys PLC - Introduction to the 4 basic concepts of PLC signals
Analog signal: refers to a continuous current signal or voltage signal, and analog signal can be divided into standard signal and non-standard signal.
Switching signal: It can be divided into active signal and passive signal, which is basically an on-off signal, and can be measured on and off with a multimeter ohm.
...
|
|
Hollysys signed a contract with Lysys for the integrated management platform project of smart tunnel of Linzhou-Changzhi Expressway in Henan
Recently, Hollysys signed a contract for the comprehensive management platform project of smart tunnel of Linzhou-Changzhi Expressway in Henan Province. Linzhou to Changzhi Expressway is a traffic artery that crosses the Grand Canyon of Taihang Mountain, through Henan and Shanxi, with a total of 7 pairs (14) tunnels.
|
|
Hollysys DCS - a common fault of DCS
1. Field instrument equipment failure:
Field instrumentation equipment includes various transmitters, various switches, actuators, loads and components of various temperatures that are directly connected with the production process. If the field instrument fails, it directly affects the control function of the DCS system and the operator's ...
|
|
Contact
working hours
