Currently, there are hundreds of PLC manufacturers both domestically and internationally, each with its own performance characteristics. When designing a PLC system, the first priority is to ensure production safety and reliability, guarantee quality, and improve efficiency.
When designing a PLC system, the first step is to determine the system scheme. The next step is to design and select the appropriate PLC. Selecting a PLC mainly involves determining the manufacturer and specific model. If the system scheme requires a distributed system, remote I/O system, or network communication capabilities, these requirements also need to be considered.
The general steps are as follows:
PLC Manufacturer Selection
Generally, for controlling independent equipment or relatively simple control systems, Japanese PLC products offer a certain advantage in terms of cost-effectiveness. However, for larger systems with high network communication requirements, open distributed control systems, and remote I/O systems, European and American PLCs have an advantage in network communication capabilities.
Estimation of the number of input/output (I/O) points
The number of I/O points should be determined based on the total number of all input/output points required by the control device. Generally, an expansion margin of 10% to 20% should be added as the estimated number of input/output points.
Estimation of PLC memory capacity
The total number of words in memory is calculated by multiplying the number of digital I/O points by 10 to 15, plus 100 times the number of analog I/O points (16 bits per word). An additional 25% margin is then considered for this number.
PLC communication function selection
Choose the appropriate communication method based on actual needs.
PLC Model Selection
PLCs are classified into two types according to their structure: integrated type and modular type. Integrated type PLCs have fewer and relatively fixed I/O points, so users have less room for choice and they are usually used in small control systems.
Selection of I/O modules
The functional modules include a communication module, a positioning module, a pulse output module, a high-speed counting module, a PID control module, and a temperature control module.
