Honeywell 2MLI-D28A 64-Point Digital Input Module

Honeywell 2MLI‑D28A 64‑Point Digital Input Module

Configured for high‑density 24 VDC discrete acquisition in MasterLogic platforms, the Honeywell 2MLI‑D28A (2MLI‑D28A digital input module) provides direct electrical execution of 64 sinking‑type input points with CPU‑configurable response timing and photo‑coupler isolation.

Hardware Specifications

4‑20 mA HART Loop Protocol Interaction & Channel‑to‑Channel Isolation

Although the 2MLI‑D28A is a discrete module, its photo‑coupler isolation and threshold design align with Honeywell’s mixed‑signal backplane behavior. Channel‑to‑channel isolation prevents transient coupling from adjacent analogue modules handling 4‑20 mA HART loops. The module’s fixed impedance (~5.6 kΩ) ensures predictable loading when installed near loop‑powered transmitters, while the AC 560 V isolation rating maintains stable reference behavior across grounding planes. CPU‑selectable response times allow tuning for noise‑sensitive environments where HART loop polling may introduce switching artifacts.

Frequently Asked Questions

Q: Can the 2MLI‑D28A be hot‑swapped? A: No. The module must be inserted or removed only when the MasterLogic rack is de‑energized.

Q: Does changing the CPU response‑time parameter affect backplane timing? A: No. Response‑time selection affects only input filtering; backplane scan timing is controlled by the CPU.

Q: Are the 64 points individually isolated? A: Isolation is provided per channel through photo‑couplers, but commons are grouped in 32‑point COM blocks.

Field Installation Guidelines

• Route 24 VDC discrete wiring separately from analogue or high‑energy conductors to reduce noise coupling.
• Maintain correct polarity for sinking‑type field devices.
• Use 0.3 mm² conductors as recommended to ensure proper terminal engagement.
• Ensure connectors are fully seated to avoid intermittent channel behavior.
• Terminate shields at a single grounding point to prevent ground‑loop interference.
• Verify CPU response‑time settings when integrating with fast‑acting sensors or interlocks.
• Label all field wiring to support maintenance and troubleshooting.