Programmable Logic Controller (PLC) of the workload of the design and

construction of the control system
Since the digital output plc using a relay control system software to replace a large number of intermediate relay, time relays, counters and other devices, the control cabinet design and installation of wiring workload greatly reduced. Meanwhile, plc controller manufacturer user program can simulate debugging in laboratory, but also reduce the workload of site commissioning. Also, due to the low failure rate micro smart plc and strong monitoring, modular, etc., so maintenance is also very convenient.

Programmable Logic Controller (PLC) software measures:

We have a strong self-test and protection.
① fault detection - software periodically to detect the external environment, such as a power failure, under voltage, battery voltage is too low and strong interference signals. So that timely treatment.
② Information Protection and Recovery - When sporadic fault condition occurs, does not destroy the plc cpu modules's internal information. Once the fault condition is removed, you can return to normal, continue the original program of work. Therefore, intelligent plc when the fault condition is detected, immediately put the current state stored in the memory, software with the memory is closed to the memory of any action to prevent the storage of information is obliterated.
③ Set the Watchdog WDT (Watchdog) - If the program execution time per cycle than the WDT specified time, indicating the program into an infinite loop, call the police.
④ strengthen inspection and verification procedures - once the program is wrong, call the police, and stops executing.
⑤ the program and dynamic data backup battery - after a power outage, use battery-powered back-up, and information about the status will not be lost.
Plc modules factory pilot project, there is an immunity test. It is required to withstand the amplitude of 1000V, the rise time 1nS, a pulse width of the pulse 1μS of interference. In general, the average time between failures of up to hundreds of thousands - tens of millions of hours; the system can be made up to 4 to 50,000 hours or longer.

Programmable Logic Controller (PLC) hardware measures:

The main modules are used large-scale or large scale integrated circuits, a large number of switching operations performed by non-contact electronic memory, I / O system design have improved the channel protection and signal conditioning circuit.
① shield - to power transformers, CPU, programmers and other major components, the use of electrical conductivity, magnetic shielding material good, to prevent outside interference.
② filter - the power supply system and an input line filter in various forms, such as LC or π-type filter network to eliminate or suppress high frequency interference, but also weakened the interaction between the various modules.
③ power adjustment and protection - the core components of the microprocessor needed a + 5V supply, the use of multi-stage filter and make adjustments with the integrated voltage regulator to adapt to fluctuations in the exchange and over-grid voltage, under influence of voltage.
④ isolation - between the microprocessor and plc IO module circuits, opto-isolated, effectively isolate the electrical connection between the I / O interface with the CPU contact, reducing failures and malfunctions; between the I / O port also isolated from each other.
⑤ with modular structure - This structure helps in case of failure to repair short. Once identified a faulty module can easily be replaced quickly, allowing the system to resume normal work; also helps to accelerate find the cause of the fault.

Programmable Logic Controller (PLC) features

Industrial control equipment reliability requirements:
① MTBF long time
② time to repair (MTTR) Short
Any failure electronic devices, usually two:
① sporadic fault. Due to the harsh external environment, such as electromagnetic interference, ultra-high temperature, ultra-low temperature, over voltage, under voltage failure caused by vibration and so on. Such failures, they do not cause damage to system components, once the environmental conditions return to normal, the system also will return to normal. But for plc analog input output module, the rear outside influence, the information stored inside may be damaged.
② permanent failure. Since the components can not be restored and the destruction caused by the fault.
If we can limit the occurrence of sporadic fault condition, the consequences will not be affected if the plc IO module or able to make impact in harsh environments is limited to a minimum, make PLC automatically disappear after the harsh conditions return to normal, so that we can improve MTBF time; if we can increase the number of diagnostic measures and appropriate means of protection in the PLC, when a permanent failure, can quickly find the point of failure and faults locally, can reduce mean time to repair the plc communication modules. To this end, each PLC manufacturer has taken various measures in terms of hardware and software, so that PLC in addition to their strong self-diagnostic capabilities, in time with an error message, stop waiting for repair, but also make the PLC has a very strong anti-jamming capability.

CPU module key switch description

CPU module key switch description

RUN running mode and REM remote mode

Run the CPU, the user cannot be stopped by software; cannot modify the program, including a full download and online download, not mandatory, cpu modules plc programming software can not write variables (HMI can write variables); can not be reset, cold reduction and empty application.

From the "run" or "PRG mode dial to" REM "mode, CPU working mode to maintain the state, users can through software running or stopping CPU;  digital output plc can modify the program online, can force, you can also write variables can be reset, cold reduction and empty applications.