Honeywell 2MLI-D21D Digital Input Module
Product Overview
The Honeywell 2MLI-D21D is a 21-channel digital input module designed specifically for high-integrity, safety-critical automation systems. As part of Honeywell’s ML200 Series, this module features dual-redundant input capability, ensuring continuous signal availability and fault tolerance. It is used to acquire discrete signals from field devices such as switches, relays, and proximity sensors, typically in emergency shutdown (ESD), fire & gas, and turbine control systems.
Built to comply with stringent industrial safety and reliability standards, the 2MLI-D21D module supports diagnostics, channel isolation, and superior electromagnetic compatibility (EMC), making it ideal for mission-critical monitoring in hazardous industrial environments.
Key Features
-
21 Digital Input Channels – High-density module for collecting multiple field signals in one unit
-
Dual-Redundant Input Architecture – Increases reliability by accepting dual-sourced signals for each channel
-
Enhanced Diagnostics – Continuously monitors signal integrity and wiring conditions
-
Channel Isolation – Each input is electrically isolated to prevent fault propagation
-
LED Indicators – Real-time channel status display for simplified maintenance
-
Wide Voltage Range Support – Accepts industry-standard 24 VDC digital input signals
-
ML200 System Integration – Seamless connection with Honeywell safety and automation systems
-
DIN-Rail or Panel Mountable – Flexible installation options for various control cabinet designs
Technical Specifications
3.1 Dimensions and Weight
| Item | Specification |
|---|---|
| Dimensions | 135 x 115 x 30 mm |
| Weight | Approx. 0.35 kg |
3.2 Electrical Characteristics
| Item | Specification |
|---|---|
| Input Channels | 21 dual-redundant inputs |
| Nominal Input Voltage | 24 VDC |
| Input Voltage Range | 18 to 30 VDC |
| Logic High Threshold | ≥ 15 VDC |
| Logic Low Threshold | ≤ 5 VDC |
| Input Impedance | Approx. 3 kΩ |
| Channel Isolation | >1500 VDC channel-to-system |
3.3 Environmental Characteristics
| Item | Specification |
|---|---|
| Operating Temperature | 0°C to +60°C |
| Storage Temperature | -40°C to +85°C |
| Relative Humidity | 5% to 95% RH (non-condensing) |
| Vibration/Shock | IEC 60068 compliant |
| Protection Class | IP20 |
3.4 System Compatibility
| Item | Specification |
|---|---|
| System | Honeywell ML200 Series |
| Configuration Platform | Honeywell system configuration tools |
| I/O Redundancy | Dual-signal support per channel |
Industry Applications
-
Emergency Shutdown Systems (ESD) – Monitors critical field inputs for immediate system response
-
Fire & Gas Detection – Interfaces with flame detectors, smoke sensors, and alarm contacts
-
Oil & Gas Processing – Ensures safe operation through reliable digital signal monitoring
-
Power Generation – Captures breaker, relay, and interlock statuses in turbine and substation controls
-
Chemical and Petrochemical Plants – Supports SIL-rated safety instrumented systems (SIS)
The Honeywell 2MLI-D21D Digital Input Module delivers unmatched reliability and diagnostic performance for demanding safety applications. With dual-redundant input channels, robust electrical isolation, and seamless ML200 system integration, it is a trusted solution for industrial facilities requiring uninterrupted digital signal acquisition and safety assurance.
