When purchasing a PLC , the following points must be noted, as they are the only direct indicators of a PLC's performance level.
1. Storage capacity
Storage capacity refers to the capacity of the user program memory. A larger user program memory capacity allows for the creation of more complex programs. Generally, a small PLC has a user memory capacity of several thousand words, while a mainframe PLC has a user memory capacity of tens of thousands of words.
2． I/O points
The number of input/output (I/O) points is the total number of input and output signals that a PLC can accept, and it is an important indicator of PLC performance. The more I/O points, the more external input and output devices can be connected, and the larger the control scale.
3. Scanning speed
Scan speed refers to the speed at which a PLC executes a user program, and it is an important indicator of PLC performance. Scan speed is generally measured in the time required to scan 1K words of user program, usually expressed in milliseconds per K words. PLC user manuals typically provide the time taken to execute each instruction; by comparing the times taken by different PLCs to perform the same operation, the scan speed can be measured.
4. Functions and Number of Instructions
The strength and quantity of instruction functions are also important indicators for measuring PLC performance. The more powerful and numerous the programming instructions, the stronger the PLC's processing and control capabilities, and the simpler and more convenient the user programming process, making it easier to complete complex control tasks.
5. Types and quantities of internal components
When programming a PLC, a large number of internal components are needed to store variables, intermediate results, hold data, timers, counters, module settings, and various flags. The more types and quantities of these components there are, the stronger the PLC's ability to store and process various information.
6. Special Functional Units
The number and strength of special function units (SMUs) are important indicators for evaluating PLC products. In recent years, PLC manufacturers have attached great importance to the development of SMUs, resulting in an increasing variety of SMUs with increasingly powerful functions, thus expanding the control capabilities of PLCs.
7. Scalability
The scalability of a PLC includes expansion of the number of I/O points, storage capacity, networking capabilities, and various functional modules. When selecting a PLC, its scalability is often a key consideration.
