The number of input and output points of a PLC indicates how many input signals the PLC can accept from the outside and how many output signals it can output to the outside. In fact, it is the number of input and output terminals of the PLC.
There are two common types of user memory used in PLCs: random access memory (RAM) and erasable programmable read-only memory (ROM). User programs are usually stored in RAM to prevent data loss during power outages.
1. Small PLC
The number of input/output points is less than 128, and the user memory capacity is less than 2KB. Small PLCs are suitable for on/off control applications, and have functions such as logic operations, calculations, and timing. They can realize conditional control, timing, counting control, and sequential control.
2. Medium-sized PLC
The number of input/output points ranges from 256 to 1024, and the user program memory capacity ranges from 2 to 8 KB. In addition to the aforementioned logic operation functions, medium-sized PLCs also have analog input/output, data transmission, and data communication functions. These PLCs often adopt a modular structure, allowing users to add I/O modules and analog modules according to control requirements. Therefore, they can automate complex industrial production processes involving both digital and analog signals.
3. Large-scale PLC
The PLC has 1024 input/output points, with a maximum of 8192 points, and a user program memory capacity of 8KB or more. It features abundant I/O modules to adapt to various control requirements. Besides ladder logic programming, it can also be programmed using high-level languages such as BASIC and C. It possesses functions including data processing, module adjustment, real-time interruption, process monitoring, network communication, file processing, remote control, and intelligent control. It can also form a distributed control system or an automation network for the entire factory.
