RAFI controller, German RAFI model, RAFI price

The RAFI controller is an electronic system for digital arithmetic operations, specifically designed for industrial environments. It uses a programmable memory to execute instructions for stored logic operations, sequential control, timing, counting, and arithmetic operations. It controls various types of mechanical equipment or production processes through digital or analog input (I) and output (O) interfaces. The programmable controller was developed based on electrical control technology and computer technology, and has gradually evolved into a new type of industrial control device with a microprocessor at its core, integrating automation technology, computer technology, and communication technology. PLC has been widely used in the automatic control of various production machinery and processes, becoming one of the most important, widespread, and frequently applied industrial control devices. It is recognized as one of the three pillars of modern industrial automation (PLC, robots, CAD/CAM).

RAFI controller composition

(1) Reference element: Provides the input quantity corresponding to the desired output. 2) Comparison element: Calculates the deviation between the input quantity and the feedback quantity, often implemented using integrated operational amplifiers (op-amps). 3) Amplification element: Since the deviation signal is generally small and insufficient to drive the load, an amplification element is required, including voltage amplification and power amplification. 4) Actuating element: Directly drives the controlled object to change the output quantity. Common examples include motors, control valves, and hydraulic motors. 5) Measurement element: Detects the controlled variable and converts it into the required electrical signal. Commonly used in control systems are tachogenerators and optical encoders for speed detection; resolvers and synchros for position and angle detection; current transformers for current detection; and thermocouples for temperature detection. These detection devices generally convert the detected physical quantities into corresponding continuous or discrete voltage or current signals. 6) Correction element: Also known as a compensation element, it is an element with structure and parameters that are easy to adjust. It is connected in the system in series or via feedback to perform the required arithmetic functions and improve system performance. Depending on its position in the system, it can be referred to as a series correction element or a feedback correction element.

RAFI controller structure

1) Central Processing Unit (CPU): The Central Processing Unit (CPU) is the control center of the PLC, acting as its neural core. Each PLC system has at least one CPU. It receives and stores user programs and data entered from the programmer according to the functions assigned by the PLC system program; checks the status of the power supply, memory, I/O, and watchdog timer, and diagnoses syntax errors in the user program. When the PLC is running, it first receives the status and data from field input devices via scanning and stores them in the I/O image area. It then reads the user program line by line from the user program memory, interprets the commands, and executes logical or arithmetic operations as instructed, sending the results to the I/O image area or data registers. After all user programs are executed, the output states in the I/O image area or data in the output registers are transferred to the corresponding output devices. This cycle continues until operation stops. To further improve the reliability of the PLC, large-scale PLC systems often use dual CPU redundant systems or triple CPU voting systems. Thus, even if one CPU fails, the entire system can continue to operate normally. CPU speed and memory capacity are important parameters of the PLC, determining the working speed of the PLC, the number of I/O points, and software capacity, thereby limiting the control scale. 2) Memory: System program memory stores system software; user program memory stores PLC user applications; data memory stores intermediate states and information during PLC program execution, equivalent to the RAM of a PC. 3) Input/Output Interface (I/O module): The interface between the PLC and electrical circuits is completed through the input/output section (I/O). The I/O module integrates the PLC I/O circuitry. Its input latch reflects the input signal status, and output points reflect the output latch status. Input modules convert electrical signals into digital signals for the PLC system, while output modules do the reverse. I/O modules are divided into digital input (DI), digital output (DO), analog input (AI), and analog output (AO) modules. 4) Communication Interface: The main function of the communication interface is to enable data exchange (communication) between the PLC and external devices. Communication interfaces come in various forms, with the most basic being standard serial interfaces such as UBS, RS-232, and RS-422/RS-485. Connections can be made using multi-core cables, twisted pairs, coaxial cables, or optical fibers. 5) Power Supply: The PLC power supply provides operating power for the PLC circuitry and plays a crucial role in the entire system. A good, reliable power supply system is the most basic guarantee for the PLC. Generally, if AC voltage fluctuation is within +10% (+15%), the PLC can be directly connected to the AC mains without additional measures. Power input types include: AC power (220VAC or 110VAC) and DC power (commonly 24VDC).

RAFI controller features

1) High reliability and strong anti-interference capability: PLC uses software to replace a large number of intermediate relays and time relays, leaving only a small amount of hardware related to inputs and outputs. Wiring can be reduced to 1/10~1/100 of that in relay control systems, significantly reducing failures caused by poor contact. High reliability is a key performance metric for electrical control equipment. PLC employs modern large-scale integrated circuit technology, strict manufacturing processes, and advanced internal anti-interference techniques, resulting in high reliability. For example, the mean time between failures (MTBF) for the Mitsubishi F series PLC is as high as 30 hours. Some PLC systems using redundant CPU have even longer MTBFs. In terms of external circuitry, using PLC to form a control system reduces electrical wiring and switch contacts to one-hundredth or even one-thousandth of those in equivalent relay-contactor systems, greatly lowering failure rates. Additionally, PLC features hardware self-diagnosis for faults, issuing alarm information promptly when issues arise. In application software, users can also incorporate self-diagnostic programs for peripheral devices, providing fault self-diagnosis protection for circuits and equipment other than the PLC. Thus, it is no surprise that the entire system exhibits extremely high reliability. 2) Complete hardware support, comprehensive functions, and strong applicability: PLC has evolved into a range of serialized products in large, medium, and small sizes. It is standardized, serialized, and modular, equipped with a wide variety of hardware devices for user selection. Users can flexibly and conveniently configure systems to create setups with different functions and scales. Installation and wiring of PLC are also convenient, typically using terminal blocks for external connections [3]. PLC has strong load-driving capability and can directly drive general solenoid valves and AC contactors, making it suitable for industrial control applications of various scales. In addition to logic processing, modern PLC units mostly have comprehensive data arithmetic capabilities, suitable for various digital control fields. A large number of PLC function units have emerged, allowing PLC to penetrate various industrial controls such as position control, temperature control, and CNC. Enhanced PLC communication capabilities and developments in human-machine interface technology make it very easy to use PLC to compose various control systems. 3) Easy to learn and use, popular among engineering technicians: As a general-purpose industrial control computer, PLC is industrial control equipment oriented towards industrial and mining enterprises. Its interfaces are easy to use, and its programming languages are easily accepted by engineering technicians. The graphical symbols and expression methods of ladder diagram language are quite similar to relay circuit diagrams. Using only a few digital logic control instructions of the PLC, the functions of relay circuits can be easily realized. This opens a convenient door for those unfamiliar with electronic circuits, computer principles, and assembly language to use computers for industrial control. 4) Easy to modify: System design, installation, and commissioning require little effort, maintenance is convenient, and modifications are easy. PLC ladder programs generally adopt sequential control design methods. This programming method is regular and easy to master. For complex control systems, the design time for ladder diagrams is much less than that for designing relay system circuit diagrams. PLC uses stored logic to replace wiring logic, greatly reducing external wiring of control equipment, significantly shortening the design and construction cycle of control systems, and making maintenance easier. More importantly, it makes it possible to change the production process of the same equipment by changing the program. This is very suitable for production scenarios with high variety and small batches. 5) Small size, light weight, and low energy consumption: Taking ultra-small PLC units as an example, recently produced models have base dimensions smaller than 100mm, equivalent to the size of only a few relays. Thus, the volume of switchgear cabinets can be reduced to 1/2~1/10 of the original size. Its weight is less than 150g, and power consumption is only a few watts. Due to its small size, it is easy to install inside machinery, making it an ideal controller for mechatronics integration.

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