Mitsubishi PLC control system design to save input / output point skills - Database & Sql Blog Articles

Probe domestic switch needle KG-300K, with a head diameter of 3.0mm, is a normally open switch needle.

100V, 250mA, surface mount, high-speed switching diode.

Photocoupler – an essential component for electrical isolation in control systems.

In engineering design, it's common to face situations where the control system has too many signals, but the PLC input points are limited. Adding more hardware can lead to extra costs. The challenge is how to maximize the use of existing equipment and process as much data as possible. This is a topic worth exploring in depth.

(1) Methods to Reduce the Number of Input Points Required
a. Use group input automatic programs and manual programs that don’t run simultaneously. You can combine these signals and input them into the PLC based on different control states.
b. Merge contacts for input. For example, in a two-start, three-stop relay-contactor control system, the three stop buttons can be connected in series to one input point, while the two start buttons go to another. This significantly reduces the number of input points used without affecting functionality.
c. Fully utilize the internal functions of the PLC. Use the transfer instruction to connect a single switch to an input, acting as a manual/automatic mode selector.
Differentiate between manual and automatic operations using branch instructions. With counting commands or shift registers, you can also implement single-button start/stop by alternating outputs.

(2) Methods to Reduce the Number of Output Points Required
a. If multiple loads share the same on/off state, they can be paralleled to the same output terminal, provided the PLC’s output power allows it. This means one output point can drive multiple loads.
b. When there are m BCD display devices showing PLC data, each BCD display can occupy 4 output terminals in parallel. This approach optimizes the usage of output points.
c. Some control logic is simple and doesn't participate in the work cycle. These can be controlled without the PLC, saving valuable output points for more critical tasks.

By applying these strategies, engineers can optimize both input and output resources, making the most out of available PLC capabilities while reducing unnecessary hardware investment. It's all about smart design and efficient use of existing components.