4256A26G01 is a dedicated remote I/O expansion interface board of Westinghouse Emerson 4256 series Ovation WDPF distributed control system, matched and used with MRC main remote control boards (4256A25 series). It acts as a signal expansion bridge between the MRC master card and multiple groups of field remote I/O sub-racks, expanding the access capacity of remote field stations and undertaking secondary scheduling, signal buffering and bus signal shaping of remote communication data. This board is fully backward compatible with all mainstream MRC master control versions, featuring optimized bus signal drive capability and extended channel carrying capacity compared with old-generation expansion boards. It adopts multi-layer high-temperature resistant FR-4 industrial PCB and full enclosed electromagnetic shielding layout, with 1000V AC/DC galvanic isolation between field wiring terminals and internal logic circuits to eliminate electromagnetic noise interference generated by inverters, high-voltage switchgears and large rotating equipment in heavy industrial sites. Each module undergoes strict factory verification including 72-hour high-low temperature cyclic aging, full-load bus communication burn-in and channel fault simulation test. It supports single-slot hot-swappable installation without overall DCS system shutdown, integrates multi-stage surge, overvoltage, overcurrent, reverse polarity and short-circuit hardware protection, and carries LED diagnostic indicators for power, bus link and channel fault to realize rapid on-site troubleshooting, effectively improving the expandability of large multi-station DCS systems and reducing unplanned production downtime.