Metso IOP331 high-density Digital Input Module
The Metso IOP331 is a high-density Digital Input Module designed for the Metso DNA and maxDNA Distributed Control Systems.
It is the primary interface for bringing discrete “On/Off” signals from the field into the control logic.
1. Introduction
The IOP331 provides 16 channels of digital input, specifically designed to monitor the status of field contacts such as limit switches, pushbuttons, and auxiliary relay contacts.
Its primary role is to sense whether a circuit is open or closed and transmit that status to the Distributed Processing Unit (DPU).
It is built for the high-reliability requirements of power plants and heavy industrial processing.
2. Technical Parameter Table
| Parameter | Specification |
| Model Number | IOP331 (Part No: 181551) |
| Input Channels | 16 Channels |
| Input Voltage | 48V DC (Standard wetting voltage) |
| Input Current | Approx. 5-7 mA per channel |
| Isolation | 1500V AC (Field-to-Logic Galvanic Isolation) |
| Filtering/Debounce | Software configurable (typically 5–20 ms) |
| Status Indicators | 16 Front-panel LEDs (one per channel) |
| Power Consumption | Low power CMOS design |
| Operating Temp | 0°C to +55°C |
| Connection Type | Interface with CPO331 or similar terminal blocks |
3. Related Models
The IOP331 is often used in conjunction with other discrete and analog modules in the same rack:
IOP330: The 24V DC version of this digital input module.
IOP351: The 16-channel Relay Output module (the “action” counterpart to the IOP331’s “sensing”).
IOP332: A variant designed for 125V DC digital inputs.
CPO331: The specialized Connection Pole/Terminal Block required for field wiring.
4. Application Cases
Sequence of Events (SOE): Monitoring high-speed trips and status changes in power plant turbines.
Safety Interlocks: Reading the position of emergency stop buttons and safety gates.
Motor Status: Confirming “Run” or “Stop” feedback from motor starters and Variable Frequency Drives (VFDs).
Valve Position: Detecting “Fully Open” or “Fully Closed” states via limit switches on pneumatic valves.
| CANON | DDR2-1A |
| CASH | E-55 |
| CAUTION | 3L046-5 KPC CG |
| CCC | TIOC-555HD |
| CCC | TMPU-1002 |
| CCC by Honeywell | IOC-555-D |
| CCC BY HONEYWELL | PSMU-350-3 |
| CCC by Honeywell | TIOC-555HD |
| CCC by Honeywell | TMPU-1002 |
| CISCO | ASSY#68-0208-03B0/73-1669-06B0 |
| CISCO | N7K-M148GT-11L |
| CISCO | IE-4000-16GT4G-E |
| Cisco | CSACS-1121-K9 |
| CKD | LYX-0507 |
5. Product Advantages and Features
Built-in Diagnostics: The module monitors its own internal health and communication status with the DPU, alerting operators to module hardware failures immediately.
Optical Isolation: Utilizes optocouplers to ensure that high-voltage spikes or electrical noise on the field wiring do not damage the central processor.
Wetting Voltage Flexibility: While 48V is standard for the 331. it is engineered to handle the voltage drops common in long-distance field wiring.
Ease of Maintenance: Individual channel LEDs allow for “at-a-glance” troubleshooting—technicians can verify signal presence without opening the software.
6. Other Models in the Same Series
The IOP331 is a staple of the maxPAC / Metso DNA I/O architecture:
DPU4E / DPU404: The controllers that process the digital logic from the IOP331.
IOP302: 16-channel Analog Input (4-20mA).
IOP320: 8-channel Analog Output (4-20mA).
PSM303: Power Supply Module for the I/O bus.
IOP331