Valmet ABMB MT838 – Bus Mother Board PCB

The Valmet ABMB MT838 is a printed circuit board that serves as a bus mother board (backplane) for Valmet DNA and Metso automation systems. It provides the mechanical and electrical interface for plug‑in modules, distributing power and data buses across a series of slots. The MT838 is designed for medium‑density I/O configurations, typically offering 8 to 12 slots. It ensures low‑impedance power delivery and high‑speed signal routing for reliable operation of digital and analogue I/O cards, communication modules, and CPU boards.

Slot Architecture and Bus System

The MT838 features a backplane with multiple 96‑pin DIN 41612 connectors, arranged with a standard pin‑out that supports both parallel and serial communication buses. The parallel bus handles high‑speed I/O data transfers, while a separate CAN‑based serial bus supports configuration, diagnostics, and firmware updates. The bus lines are terminated with active or passive termination networks that can be configured via onboard jumpers. The board includes a clock distribution network to provide synchronized timing signals to all slots.

Power Distribution and Monitoring

The backplane distributes +5 V, +24 V, and ±15 V from a rear power input to each slot. The power traces are oversized to handle high current loads with minimal voltage drop (less than 2 % at full load). Each power rail is filtered with electrolytic and ceramic capacitors near each connector to suppress high‑frequency noise. The board includes a power status monitor with LEDs for each rail; an open‑collector output provides a remote fault signal in case of undervoltage or overcurrent.

Signal Integrity and Shielding

The MT838 is manufactured with a six‑layer PCB stackup, including dedicated ground and power planes. Critical data lines are impedance‑controlled (60 Ω differential) and length‑matched to ensure reliable data transfer at speeds up to 20 MHz. The board is designed with a ground fill around all signal tracks to reduce crosstalk and radiated emissions. An EMI shielding bar can be attached to the front edge for additional suppression.

Mechanical and Environmental Specifications

The board is a 6U Eurocard (233 mm x 160 mm) with a thickness of 2.0 mm. It is made of high‑TG FR‑4 and coated with a conformal lacquer. Operating temperature is 0 °C to +55 °C; storage from ‑40 °C to +85 °C; humidity 5‑95 % non‑condensing. The board meets UL 94 V‑0 and IEC 61010‑1 standards.

Connectors and Interface

It includes 8 (or 12) 96‑pin DIN connectors for modules, a 20‑pin power input connector, a 50‑pin header for external bus expansion, and a 10‑pin diagnostic header. Test points are provided for all power rails and bus signals.

Installation and Setup

Mount the backplane into the subrack. Connect the power supply. Set the bus termination jumpers based on the rack position. Insert the modules into the slots. No software configuration is required.

Applications

The MT838 is used in Valmet I/O racks for paper machines, boilers, and chemical reactors, providing the foundation for CPU and I/O modules.

Maintenance

Inspect for dust and check the power LEDs. The board is passive and reliable.

Conclusion

The Valmet ABMB MT838 offers a robust, high‑performance backplane solution, ensuring reliable interconnectivity for modular automation systems.