Programmable Logic Controller (PLC) is an electronic system of digital operations designed for use in industrial environments. It uses a programmable memory to store instructions to perform logical operations, sequential control, timing, counting, and arithmetic operations, and to control various types of mechanical equipment or production processes through digital or analog inputs and outputs.
PLC technology:
1, open-loop control
Open-loop control of switching quantities is the most basic control function of the PLC. PLC's instruction system has a powerful logic operation ability, it is easy to realize timing, counting, sequence (step) and other logic control methods. Most PLC is used to replace the traditional relay contactor control system.
2, analog closed-loop
For analog closed-loop control system, in addition to switching inputs and outputs, but also analog inputs and outputs, in order to sample the inputs and regulate the output to achieve the temperature, flow, pressure, displacement, speed and other parameters of continuous regulation and control. The current PLC not only large, medium-sized machine with this function, but also some small machines also have this function.
3, digital control
Control system with a rotary encoder and pulse servo device (such as stepper motors), the PLC can be used to achieve the function of receiving and outputting high-speed pulses to achieve digital control, the more advanced PLC has also been developed specifically for the digital control module to achieve the function of interpolation of curves, and recently introduced a new type of motion unit module, but also to provide a digital control technology programming language, so that the digital control technology, so that the PLC has a digital control system, so that the digital control system is not only large, medium-sized machines have this function, but also some small machines also have this function. Programming language for digital control technology, so that the PLC to achieve digital control is more simple.
4, data acquisition and monitoring
Because the PLC is mainly used for on-site control, so the collection of on-site data is a very necessary function, based on the PLC is connected to the upper computer or touch screen, you can observe the current value of these data, but also timely statistical analysis.
Some PLCs have a data logging unit, you can use a general personal computer memory card inserted into the unit to save the collected data. another feature of the PLC is the self-test signal. Using this feature, the PLC control system can realize white diagnostic monitoring, reduce system failure, improve system reliability.
Expanded Information:
In the manufacturing industry, there are a large number of switching-quantity-based open-loop sequential control, which carries out sequential actions in accordance with logical conditions and chronological actions; there is also a chain of protection actions in accordance with the logical relationship between the sequence, timing is not related to the control of interlocking protective actions; as well as a large number of switching-quantity, pulse-quantity, timing, counter, analog override, alarm, and other state-quantity-based - off-line control, which can be used to control the operation of the system. Alarms and other state quantities of the main - discrete amount of data acquisition and monitoring.
Because of these control and monitoring requirements, so that the PLC developed to replace the relay line and sequence control-based products. PLC manufacturers in the original CPU template on the gradual increase in a variety of communication interfaces, fieldbus technology and Ethernet technology is also synchronized with the development of the PLC's wider and wider range of applications. PLC has a stable and reliable, inexpensive, full-featured, flexible and easy to apply, easy to operate and maintain the advantages, which is the fundamental reason for its lasting market share.
The hardware of PLC controller itself adopts the block structure, with motherboard, digital I/O template, analog I/O template, and special positioning template, barcode recognition template and other modules, users can use the motherboard to expand according to the need or use the bus technology to equip the remote I/O slave to get the desired I/O number.
PLC in the realization of a variety of quantities of I / O control at the same time, but also has the ability to output analog voltage and digital pulse, so that it can control a variety of can receive these signals servo motors, stepper motors, inverter motors, etc., coupled with the touch screen of the human-computer interface support, Schneider's PLC can satisfy your needs at any level in the process control.
Baidu Encyclopedia-Programmable Logic Controller