To determine whether the number of I/O points of the PLC is sufficient, it is necessary to comprehensively consider the current needs, future expansion needs and some special situations. The following is a detailed introduction to the judgment method:
Count the number of I/O points required for existing equipment
Clear equipment type: In industrial automation production, there are many types of equipment involved, and each device has different requirements for I/O points. For example, common buttons, limit switches, etc. are used as input devices to input signals to the PLC; while contactors, solenoid valves, etc. are used as output devices to receive control signals from the PLC.
Count the number: Carefully count the number of I/O points required for each device, and add up the number of points required for all input devices and output devices to obtain the number of input points and output points actually required by the current production system. For example, there are 10 buttons and 5 limit switches on a production line as input devices, and each button and limit switch occupies 1 input point, so a total of 15 input points are required; there are 8 contactors and 3 solenoid valves as output devices, and each contactor and solenoid valve occupies 1 output point, so a total of 11 output points are required.
Consider future expansion needs
Expanding production scale: In order to adapt to market demand, enterprises may upgrade and renovate production lines and add production equipment. This requires reserving a certain number of I/O points to meet the needs of new equipment to access PLC. For example, if 5 sensors and 3 actuators are expected to be added in the future, 5 input points and 3 output points need to be reserved.
Function expansion: In addition to adding equipment, it is also possible to optimize the production process and add new control functions. These new functions often also require corresponding I/O point support. For example, there is no link for product quality inspection in the original production process. If this function is planned to be added later, it may be necessary to add several sensors to detect product size, weight and other parameters, which requires additional input points.
Reserve a certain number of spare points
Deal with emergencies: In the actual production process, some unexpected situations may be encountered, such as equipment failure replacement, temporary addition of test points, etc. Reserving spare points can facilitate the rapid resolution of these problems without replacing the PLC and ensure the continuity of production. Generally speaking, the number of spare points should account for about 10% – 20% of the total number of I/O points. For example, if a total of 30 I/O points (15 input points and 15 output points) are currently required, and 15% of the spare points are reserved, then an additional 4 – 5 I/O points need to be reserved.
Considerations for special cases
Signal type and isolation requirements: Some special signal types, such as analog signals, high-speed pulse signals, etc., may require special I/O modules to process. Moreover, in order to ensure the stability and anti-interference ability of the signal, different types of signals may need to be isolated, which will also occupy additional I/O points. For example, an analog input signal may require an analog input module, which may occupy multiple I/O channels.
Redundant design: For some production systems with extremely high reliability requirements, redundant design may be adopted, that is, equipped with spare I/O modules or PLCs. Redundant design will increase the usage of I/O points, but it can improve the reliability and stability of the system, ensuring that the system can still operate normally when a module fails.
