Valmet Metso 181226 Digital Input Module – Rev B2/B3

The Valmet Metso 181226 is a 32‑channel digital input module designed for high‑density discrete signal acquisition in industrial control systems. Available in revisions B2 and B3 (with minor component and firmware optimizations), this module accepts 24 V DC inputs from limit switches, pushbuttons, proximity sensors, and relay contacts. It is fully compatible with the Valmet DNA and Metso I/O platform, offering reliable status monitoring for logic and interlock circuits.

Electrical Input Specifications

Each of the 32 inputs is rated for a nominal voltage of 24 V DC (range 18‑30 V DC) with a typical input current of 5 mA at 24 V. The threshold for logic high is 11 V, and low is 5 V, providing good noise immunity. Inputs are configured as sinking (negative logic) by default, but can be changed to sourcing via jumper settings. An integrated input debounce filter can be set to 0.5, 1, or 3 ms to eliminate switch bounce.

Isolation and Protection

The module provides 1500 V AC isolation between the inputs and the system bus, and groups of 8 inputs share a common return. Each input includes a transient voltage suppressor and reverse‑diode protection against accidental reversal of field wiring. The board also has a fuse on the common power line to protect against overcurrent, with an LED indicating fuse status.

Diagnostic Features

Revision B2/B3 adds enhanced diagnostics, including open‑wire detection for inputs that are supposed to be normally closed, and short‑to‑ground detection for outputs (not applicable here, but useful for adjacent modules). A module status LED (green/red) signals power‑on, communication loss, or internal fault. Each channel also has a dedicated LED that lights when the input is energized.

Communication and Data Mapping

The 181226 module communicates with the host controller via the Valmet backplane protocol, updating the input image at a typical rate of 1 kHz. The 32‑bit status word is mapped to the controller's memory, where each bit corresponds to one channel. The module supports event‑driven interrupts, allowing the controller to respond immediately to critical input changes without polling.

Hardware and Mounting

This module is a 6U x 4HP Eurocard with a 96‑pin DIN connector for backplane attachment. It is designed for mounting in a Valmet subrack with forced‑air cooling. The field connections are made via a separate 64‑pin terminal block cable harness, which is ordered separately. The module weighs approximately 0.5 kg and is easily removable with the front handle.

Environmental and Compliance

Operating temperature: ‑20 °C to +65 °C; storage: ‑40 °C to +85 °C. Humidity tolerance is 5‑95 % non‑condensing. The board is RoHS compliant and carries CE certification. It has been tested for vibration (2 g) and mechanical shock (30 g).

Application Areas

Common applications include monitoring motor starter status, valve position feedback, conveyor belt sensors, and emergency stop circuits. In a paper mill, it collects signals from felt position indicators, doctor blade limit switches, and lubrication system pressure switches. Its high channel count reduces the number of modules and wiring, simplifying panel design.

Installation and Commissioning

Before installing, verify that the rack slot is correctly configured for digital input modules. Insert the board firmly and secure with the locking screws. Connect the field wiring harness, ensuring that the common returns are correctly wired to the module's return terminals. Commission with the system engineering tool by assigning each input to a tag name and setting the debounce time as required.

Maintenance and Spare Parts

Regular inspection should focus on the LED status indicators and the cleanliness of connector pins. If a module fails, it can be replaced while the system is powered (hot‑swap) provided that the rack supports it and the controller is appropriately configured. Spare modules are readily available from Valmet support.

Conclusion

The Valmet Metso 181226 digital input module (Rev B2/B3) offers a cost‑effective, dense, and reliable solution for digital signal acquisition. Its advanced diagnostics and robust construction make it a trusted component in critical automation systems.