Hello PLC professionals and technicians! As we all know, PLCs (Programmable Logic Controllers) are essential components in industrial automation. They play a crucial role in controlling and monitoring various processes in industries such as manufacturing, automotive, and energy. The heart of a PLC is its CPU (Central Processing Unit) and memories, which store and execute the program to control the connected devices. In this article, we will discuss the commonly used CPUs and memories in PLCs, their features, and their applications. Let's dive in!
CPU Types: The CPU is the brain of a PLC, responsible for processing and executing the program instructions. PLCs use different types of CPUs based on their application and requirements. The most commonly used ones are:
1. Microprocessor-based CPU: This type of CPU is widely used in small to medium-sized PLCs. It contains a microprocessor, memory, and I/O interfaces on a single chip. The program is stored in the internal memory, and the CPU executes the instructions sequentially. These CPUs are cost-effective and suitable for simple applications with less I/Os.
2. Microcontroller-based CPU: Similar to microprocessor-based CPUs, microcontroller-based CPUs also have a microprocessor, memory, and I/O interfaces on a single chip. The difference is that they have additional features such as timers, counters, and communication ports. These CPUs are suitable for more complex applications with up to 256 I/Os.
3. Programmable Gate Array (PGA) CPU: This type of CPU uses a reprogrammable logic device, which can be configured to perform specific functions. These CPUs are highly flexible and customizable, making them ideal for complex and high-speed applications. They are also more expensive compared to microprocessor and microcontroller-based CPUs.
4. ASIC (Application-specific integrated circuit) CPU: As the name suggests, these CPUs are designed for a specific application. They offer high performance and reliability, making them suitable for critical applications such as process control and safety systems. However, they are costly and require specialized expertise for design and programming.
Memory Types: PLCs use different types of memories to store the program, data, and system parameters. The most commonly used ones are:
1. Read-Only Memory (ROM): As the name implies, this type of memory is used to store the program and data that are not supposed to be modified. The content of ROM is non-volatile, meaning it retains the data even when the power is turned off. This makes it suitable for storing the program and system parameters in PLCs.
2. Random Access Memory (RAM): RAM is a volatile memory, which means it loses its content when the power is turned off. It is used to store temporary data and program instructions during runtime. The size of RAM in a PLC varies from 16 KB to 1 MB, depending on the application and requirements.
3. Electrically Erasable Programmable Read-Only Memory (EEPROM): EEPROM is a type of non-volatile memory that can be electrically erased and reprogrammed. It is commonly used to store user-defined data and system parameters that need to be updated periodically. PLCs use EEPROM to store data such as timers, counters, and diagnostic information.
Applications: The choice of CPU and memory in a PLC depends on the application and its requirements. For instance, a simple conveyor system can be controlled using a microprocessor-based CPU and ROM, while a complex assembly line with multiple processes may require a PGA CPU and a combination of ROM and EEPROM to store program instructions and system parameters.
Conclusion: In conclusion, CPUs and memories are the backbone of a PLC, enabling it to perform its tasks efficiently and accurately. As a professional technician, it is essential to have a good understanding of the different types of CPUs and memories and their applications to choose the right one for a specific task. We hope this article has provided you with a comprehensive introduction to the commonly used CPUs and memories in PLCs. Happy programming!
Thank you for reading!