The main difference between the Mitsubishi FX3U and FX5U PLC is that the FX5U is a newer, more advanced model from the MELSEC iQ-F Series, while the FX3U belongs to the older MELSEC-F Series. The FX5U PLC delivers faster processing, higher memory, and built-in features that make it ideal for modern automation needs. For example, the FX5U executes LD and MOV instructions in 34 nanoseconds, compared to 65 ns and 520 ns in the FX3U, which means the FX5U performs tasks almost twice as fast. It also comes with larger memory capacity (up to 128K steps), whereas the FX3U supports 64K steps. Another big upgrade is that the FX5U has built-in analog I/O (2 analog inputs and 1 analog output), eliminating the need for external modules. It also has a built-in Ethernet port for easy programming, monitoring, and data transfer — something missing in most FX3U models.
The FX5U PLC is designed with better connectivity, scalability, and security compared to the FX3U. It supports advanced communication options like Ethernet, RS-485, and CC-Link, enabling seamless connection with HMIs, inverters, and other devices. The FX3U, on the other hand, requires separate adapter modules like FX3U-ENET-ADP for network connectivity. The FX5U also introduces enhanced security functions, ensuring data protection and program integrity — an important feature for today’s industrial systems. In terms of expandability, the FX5U supports up to 512 I/O points, whereas the FX3U supports 384 I/O points. The programming software is also upgraded — FX5U uses GX Works3, while FX3U supports older versions like GX Works2. In short, the Mitsubishi FX5U PLC offers better speed, memory, networking, and control features, making it the ideal replacement for the FX3U in advanced automation applications.