PLC input and output interfaces

The programmable controller is a digital computing operation of electronic systems, specialized applications in industrial environments. It uses memory can be programmed, used in instruction execution storage logical and sequential control, timing, counting and arithmetic operations such as operations and digital or analog input (I) and output (O) through the interface, to control various type of machine or production process.
Interface Plc modules and the electrical circuit is output through the input section (I / O) to complete. plc IO module integrates the PLC's I / O circuit, the input register reflecting the input signal, the output point to reflect the state of the output latch. Input module into the electric signal into a digital signal the PLC system, the opposite output module. I / O into the digital input (DI), switching output (DO), the analog input (AI), analog output (AO) modules.

— plc input modules, a method of low-cost expansion of output module

analog output plc, a method of low-cost expansion of output module programmable controller (hereinafter referred to as PLC) because of its high reliability, simple programming, versatility, small size, compact structure, easy installation and maintenance features, in the industrial control has been widely used. PLC modules are generally divided into the following categories: digital input modules, digital output modules, analog input modules, analog output plc. In industrial control especially in the field of process control analog acquisition and control needs a relatively large amount, so the PLC analog input and output modules require more, and analog input and output modules are more expensive, increasing the analog input, output module increases the cost and reduces the cost of the entire system, limit the application of PLC. This paper presents a method based on extended analog input and output modules of communication trying to solve this problem.

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 industrial controller's internal information. Once the fault condition is removed, you can return to normal, continue the original program of work. Therefore, profibus module 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 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.