Taiwan PLC supplier talks about the comparison between PLC and control relay
Delta PLC The supplier talks about the comparison between PLC and control relay. In the field of industrial automation, programmable logic controllers (PLCs) are used as automatic control systems to become the basis of most automation systems, and they have brought unprecedented changes to industrial control. The industrial control system using PLC has incomparable advantages in terms of operation, control, efficiency and precision compared with the traditional industrial control system with relay. Although the relay control equipment used in the industrial control system will not be completely eliminated, the design idea of the industrial control designer has been changed due to the emergence of the PLC.
First, the shortcomings of control relays "
Relays have been applied to all areas of home and industrial control. They have higher reliability than previous products. However, this is also Some problems that come with it. For example, most control relays are carried out under long-term wear and fatigue working conditions, which are easy to damage. Moreover, the contacts of the relay are prone to arcing, and even melt together to cause misoperation, causing serious Consequences. Furthermore, for a specific device equipped with hundreds of relays, the control box will be bulky and cumbersome. In the case of full load, large relays will generate a lot of heat and noise, It also consumes a lot of power. And the relay control system must be manually wired and installed. If there are simple changes, it will take a lot of time and manpower and material resources to modify, install and debug.
The advantages, features and functions of the programming controller
The programmable controller is known for its small size and powerful function. It not only can easily complete the sequential logic. , motion control, timing control, counting control, digital calculation, data processing and other functions, and can establish digital and analog quantities with various types of production machinery through input and output interfaces, thus achieving automatic control of the production process. Especially now, due to The arrival of information and network era has expanded the functions of PLC, making it a strong network communication capability, which is widely used in many industries.
1. Sequence control
The sequential control is a basic field of PLCzui and a wide range of applications. The so-called sequential control is to make the various actuators of the production process automatically follow the sequence according to the sequence of the process flow under the control signal. Because it also has programming design. Flexible, fast, reliable, low cost, easy to maintain, etc., so in the realization of single machine control, multi-group control, production process control can completely replace the traditional relay contactor control system. It is mainly based on operating buttons, Limit switch and other on-site command signals and sensor signals to control mechanical moving parts The corresponding operation is carried out to achieve automatic production line control. The typical application is in the control of the automatic elevator, the automatic opening and closing of the electromagnetic cutting on the pipeline, the sequential start of the belt conveyor, etc. For example, the raw material mixing system of our branch is utilized. PLC sequential control function.
2, closed-loop process control
In the past, analog control for process control uses PID analog regulators composed of hardware circuits to achieve open and closed-loop control. It is now possible to use the PLC control system and select the analog control module. Its function is completed by software. The accuracy of the system is determined by the number of bits, which is not affected by the components, so the reliability is higher, and it is easy to implement complex control and advanced control methods. Multiple control loops and multiple control parameters can be controlled simultaneously, such as temperature, flow, pressure, speed, etc. during production.
5. Motion position control
PLC can support CNC Control and management of machine tools. In the machining industry, programmable controllers are integrated with computer numerical control (CNC) to complete the movement of machine tools. Control, its function is to accept the processing information input by the input device, after processing and calculation, send corresponding pulses to the drive device, through the stepper motor or servo motor, make the machine tool move according to a predetermined orbit to complete the multi-axis servo motor Self-control. It is currently used in applications such as centerless grinding, stamping, segmentation of complex parts, and burrs.
4. Monitoring and management of the production process
The PLC can be connected to peripherals such as display terminals and printers through the communication interface. The display as a human machine interface (HMI) is an intelligent device with a micro-processing chip. It can be combined with a PLC to replace the numerous control buttons, selection switches, signal indicators on the control cabinet, and the production process simulation screen and electricity. A large number of intermediate relays and terminal blocks in the control cabinet. All operations can be performed on the operating elements on the display. The PLC can collect and process the data in the production process conveniently and quickly, and can display the parameters to be displayed in binary, decimal, hexadecimal, ASCII characters, and the like. On the display screen, the color change of the icon reflects the operating state of the field device, such as the opening and closing of the valve, the starting and stopping of the motor, and the state of the position switch. The PID loop control uses data, bar graphs and other comprehensive methods to reflect the changes in the quantity in the production process. The operator can adjust the parameters through parameter setting. The data query can be used to find the data records at any time. The relevant production data can be saved by printing. For the convenience of future production management and analysis of process parameters.
5, network characteristics
PLC can realize the communication networking requirements between multiple PLCs or between multiple PLCs and one computer, thus forming a multi-level distributed control system, which constitutes Factory automation network.
(1) Remote control of the control system is realized by the communication module, the host computer and the corresponding software.
(2) Connect to remote client computers via a modem and public network, allowing administrators to remotely monitor the line control system.
As a general-purpose industrial controller, the programmable controller can be used in all industrial fields. At present, programmable controllers have been widely applied to various fields such as machinery, metallurgy, petroleum, chemical, textile, transportation, electric power, military, etc. at home and abroad, and have achieved considerable technical benefits. Moreover, it represents the world's advanced level of electrical control technology. It has been listed as the four pillars of industrial automation technology along with numerical control technology, CAD/CAM technology and industrial robot technology.