When purchasing a PLC control cabinet, you need to understand and evaluate it from multiple aspects. The following is a detailed introduction:
Technical specifications
PLC brand and model: PLCs of different brands and models differ in performance, function, reliability and price. Well-known brands such as Siemens, Mitsubishi, Omron, etc. have guaranteed product quality and technical support, but the price is relatively high. You need to choose the right brand and model according to the project requirements, such as the requirements for operation speed, storage capacity, communication function, etc.
I/O points: Clearly define the required input (DI) and output (DO) points, including digital and analog quantities. Consider the needs of the current project and possible future expansion needs, and reserve a certain margin. It is generally recommended to reserve 10% – 20% of the I/O points.
Operation speed and storage capacity: The operation speed is measured by the time to execute a basic instruction. For systems with high real-time requirements, you need to choose a PLC with fast operation speed. Storage capacity includes program storage capacity and data storage capacity. You need to choose the appropriate storage capacity according to the complexity of the program and the amount of data.
Communication interface and protocol: Understand the types of communication interfaces supported by the PLC control cabinet, such as RS232, RS485, Ethernet, etc., as well as communication protocols such as Modbus, Profibus, OPC, etc. Ensure that it can communicate effectively with other devices (such as host computers, sensors, actuators, etc.).
Design and manufacturing
Cabinet design: The size of the cabinet should be determined according to the installation space and internal equipment layout to ensure that there is enough space for wiring and maintenance. The protection level is usually expressed by IP (Ingress Protection), such as IP54, which means that the dustproof level is level 5 (preventing foreign objects from intruding and completely preventing dust from intruding), and the waterproof level is level 4 (preventing splashing water from intruding). The appropriate protection level needs to be selected according to the use environment.
Internal layout: A reasonable internal layout should arrange the electrical components neatly for easy wiring, operation and maintenance. Strong and weak currents should be wired separately to avoid interference. At the same time, heat dissipation and ventilation issues should be considered to ensure that the electrical components work in a suitable temperature environment.
Wiring process: The wiring should be neat and standardized, and appropriate cable specifications and colors should be used to distinguish different circuits. Cables should be firmly fixed to avoid looseness and wear. At the same time, grounding should be done well to ensure the electrical safety of the system.
Performance and reliability
Reliability indicators: Understand the mean time between failures (MTBF) and mean time to repair (MTTR) of the PLC control cabinet. The longer the MTBF, the higher the reliability of the equipment; the shorter the MTTR, the faster the equipment can resume normal operation after a failure.
Anti-interference ability: There are various electromagnetic interferences in industrial environments, such as motor starting and inverter operation. PLC control cabinets should have good anti-interference capabilities and use shielded cables, isolation transformers, filters and other measures to reduce the impact of interference on the system.
Redundant design: For some systems with extremely high reliability requirements, redundant design can be considered, such as power redundancy, CPU redundancy, communication redundancy, etc. When a device fails, the redundant device can automatically switch to ensure the normal operation of the system.
Safety and compliance
Electrical safety standards: PLC control cabinets should comply with relevant electrical safety standards, such as GB 7251 (low-voltage complete switchgear and control equipment). It has overload protection, short circuit protection, leakage protection and other functions to ensure the safety of operators and equipment.
Service and support
Supplier reputation: Choose suppliers with good reputation and rich experience.
After-sales service: Understand the after-sales service content provided by the supplier, including technical support, maintenance services, spare parts supply, etc. Ensure that you can get effective support and repair in time when there is a problem with the equipment.
Training service: Ask the supplier whether it provides training services to help operators and maintenance personnel familiarize themselves with the operation and maintenance methods of the PLC control cabinet.
Cost and budget
Purchase cost: Compare the quotations of different suppliers, including the hardware cost, software cost, transportation cost, etc. of the PLC control cabinet. Under the premise of ensuring quality and performance, choose products with high cost performance.
Operation cost: Consider the operation cost of the PLC control cabinet, such as energy consumption and maintenance cost. Choose products with low energy consumption and simple maintenance to reduce long-term operation costs.
