Honeywell MLI Series Modules

Technical Dossier

Product Details And Specifications

Honeywell MLI Series: Comprehensive Module Range and Technical Overview

The Honeywell MLI (Modular Logic Interface) series is a distributed control system (DCS) platform deployed extensively across global heavy industries, including petrochemical refineries, nuclear power facilities, offshore platforms, and large-scale chemical processing plants. Engineered under Honeywell's Process Solutions division, the MLI architecture provides deterministic scan-cycle control with high-density I/O capability, making it a standard reference platform in facilities where continuous uptime and process integrity are non-negotiable. Installed base spans North America, the Middle East, and Asia-Pacific, with many sites operating MLI hardware beyond its original design lifecycle due to the cost and complexity of full DCS migration.

The Evolution of MLI Architecture

The MLI series was introduced as part of Honeywell's TDC 3000 and PlantScape ecosystem, designed to bridge legacy relay logic with modern digital control. Early-generation MLI modules operated on a proprietary Local Control Network (LCN) backplane, using parallel bus communication at fixed scan rates. Mid-generation revisions introduced enhanced diagnostics, redundancy support, and compatibility with Honeywell's Universal Control Network (UCN). Later variants added HART pass-through capability on analog modules and expanded the digital output density to 64 points per card (as seen in the MLI-DR64H/D1). Compatibility between early and late MLI generations requires careful backplane revision matching — specifically, modules rated for the H-series backplane (suffix /H or /D1) are not interchangeable with earlier B-series racks without firmware and termination assembly verification. As Honeywell has transitioned its DCS portfolio toward Experion PKS and C300 controllers, the MLI series has entered a mature/end-of-life phase. Honeywell no longer manufactures new MLI modules; all procurement is sourced through authorized repair depots or specialist spare parts distributors.

MLI Full Catalog & Functionalities (SKU List)

Digital Output Modules

• MLI-DR64H/D1: 64-channel 24VDC digital output, H-series backplane, D1 termination assembly
• MLI-DR32H: 32-channel 24VDC digital output, H-series rack, standard density
• MLI-DR16H: 16-channel relay digital output, H-series, isolated contact outputs
• MLI-DR64B: 64-channel digital output, B-series backplane, legacy variant

Digital Input Modules

• MLI-DI64H/D1: 64-channel 24VDC digital input, H-series backplane, D1 termination
• MLI-DI32H: 32-channel 24VDC digital input, H-series rack, standard density
• MLI-DI16H: 16-channel 120VAC digital input, H-series, high-voltage variant
• MLI-DI64B: 64-channel digital input, B-series backplane, legacy variant

Analog Output Modules

• MLI-AO16H: 16-channel 4–20mA analog output, H-series, loop-powered
• MLI-AO08H: 8-channel 4–20mA analog output, H-series, isolated outputs
• MLI-AO16B: 16-channel analog output, B-series backplane, legacy variant

Analog Input Modules

• MLI-AI16H: 16-channel 4–20mA/HART analog input, H-series, HART pass-through
• MLI-AI32H: 32-channel analog input, H-series, high-density process measurement
• MLI-AI16B: 16-channel analog input, B-series backplane, legacy variant

CPU & Controller Modules

• MLI-CPU01H: Primary logic controller, H-series, redundancy-capable, LCN/UCN interface
• MLI-CPU02H: Enhanced CPU with expanded memory, H-series, dual-port network

Power Supply Modules

• MLI-PS24H: 24VDC rack power supply, H-series, redundant input capable
• MLI-PS48H: 48VDC rack power supply, H-series, for high-current I/O racks

Communication Adapters

• MLI-NIM01: Network Interface Module, LCN bus adapter, primary node interface
• MLI-UCN01: Universal Control Network adapter, UCN-to-MLI rack bridge

Sourcing Hard-to-Find & Obsolete MLI Series Parts

With Honeywell having formally discontinued MLI series manufacturing, procurement of replacement modules requires specialist sourcing. DriveKNMS maintains a dedicated inventory of tested MLI modules, including end-of-life variants such as B-series backplane cards and early CPU revisions no longer available through OEM channels. For facilities operating under long-term maintenance agreements or regulatory hold periods (common in nuclear and refining environments), DriveKNMS provides lifecycle extension support: sourcing, functional testing, and documented traceability for each unit. Requests for low-volume emergency replacements and bulk spare parts packages are both accommodated. Lead times for common H-series modules are typically 3–7 business days from confirmed stock; rare B-series and CPU modules are subject to availability confirmation.

Quality Control for the MLI Range

MLI series modules present specific test challenges due to their proprietary backplane bus protocol and multi-layer PCB construction. DriveKNMS applies a structured test protocol for each MLI unit: visual inspection for capacitor degradation, solder joint integrity, and connector pin condition; powered bench test using an MLI-compatible rack simulator to verify bus communication handshake; channel-level functional test for all I/O points (digital continuity, analog linearity across 4–20mA range, HART signal integrity where applicable); and burn-in cycle under load to screen for latent component failures. CPU modules undergo additional firmware version verification and memory integrity checks. All units are shipped with a test report and 12-month warranty against functional failure.