Metso IOP351 high-density Digital Output Module
the Metso IOP351 is a high-density Digital Output Module (specifically a Relay Output Module) designed for the Metso DNA and maxDNA Distributed Control Systems.
It is the “muscle” of the I/O rack, used to switch physical equipment on and off based on logic from the controller.
1. Introduction
The IOP351 module provides 16 discrete relay outputs. It acts as an isolation barrier between the low-voltage logic of the control system and the higher-power field devices.
Unlike standard transistor outputs, the IOP351 uses physical relay contacts, making it ideal for applications requiring robust switching of AC or DC loads, such as motor starters, solenoid valves, and indicator lamps.
2. Technical Parameter Table
| Parameter | Specification |
| Model Number | IOP351 (Part No: 181555 / 69230I351A) |
| Output Channels | 16 Channels (Relay Contacts) |
| Contact Type | Form A (Normally Open) |
| Max Switching Voltage | 125V DC / 250V AC |
| Max Switching Current | 2.0 A (Per channel, resistive load) |
| Isolation | 1500V AC (Field-to-Logic) |
| Response Time | < 10 ms (Pick/Drop) |
| Power Supply | 24V DC (Backplane logic power) |
| Status Indicators | Individual LEDs for each output channel |
| Mounting | maxPAC I/O Rack |
3. Related Models
The IOP351 is part of a broader family of discrete (digital) output modules:
IOP350: A similar 16-channel relay module, often used for lower voltage or different contact configurations.
IOP330/331: Digital Input modules used to read status (the counterpart to the IOP351).
IOP320: Analog Output module (4–20 mA) for modulating control.
CPO351: The corresponding Connection Pole (terminal block) used for field wiring.
IOP351
4. Application Cases
Motor Control: Triggering the coils of large motor starters or contactors.
Solenoid Valves: Opening and closing pneumatic or hydraulic valves in process lines.
Alarm Systems: Actuating physical horns, sirens, or strobe lights in a plant.
Interposing Relays: Serving as a master relay to trigger even larger high-voltage switchgear in power distribution.
| BUSSMANN | 25NH00 G-690 |
| BUSSMANN | 50NH00 G-690 |
| BUSSMANN | FWC-32A10F |
| CABLELINK | E87647-M |
| CABLETRON | MiniMMAC |
| CABLETRON | 9000298-02 |
| CABLETRON | 9000162 |
| CABLETRON | 9000299-02 |
| CABLETRON | 9000170-02 |
| CABLETRON | 90001666-03 |
| CABLETRON | PC-6191-C |
| Candis | TSE1111-D |
5. Product Advantages and Features
Heavy-Duty Isolation: Because it uses physical relays, it provides excellent galvanic isolation, protecting the sensitive DNA controller from electrical noise and surges on the field side.
Visual Diagnostics: Each of the 16 channels has a dedicated LED on the front panel, allowing technicians to see instantly which outputs are energized without using a multimeter.
High Density: Packing 16 relays into a single slot saves significant cabinet space compared to using external interposing relays.
Fail-Safe Operation: Can be configured to “Fail-Open” or “Hold Last State” depending on the system watchdog settings, ensuring process safety during a communication loss.
6. Other Models in the Same Series
The IOP351 belongs to the maxPAC / Metso DNA hardware lineage:
DPU4E / DPU404: The Distributed Processing Units that execute the control logic.
IOP302: 16-channel Analog Input module.
IOP303: 8-channel RTD/Resistance Input module.
PSM303: The power supply module that energizes the I/O bus.