Honeywell 2MLF-AC4H 4-Channel HART Analog Current Input Module

Product Overview

The Honeywell 2MLF-AC4H is a 4-channel HART analog current input module for the MasterLogic-200 (ML200) PLC system. It supports 4–20 mA analog input with integrated HART (Highway Addressable Remote Transducer) protocol communication, enabling bidirectional digital data exchange over the same 4–20 mA loop. This allows remote configuration, diagnostics, and multi-variable data retrieval from HART-enabled field instruments without additional wiring or communication modules.

Key Specifications

• Product Type: 4-Channel HART Analog Current Input Module
• Series: MasterLogic-200 / ML200
• Input Channels: 4
• Input Type: Current (DC 4–20 mA)
• HART Protocol: HART 5, HART 6, HART 7 (configurable)
• Resolution: 16-bit
• Conversion Speed: 250 ms per channel
• Loop Power: 24V DC (internal or external)
• Isolation: Channel-to-channel isolation
• Input Impedance: 250 Ω (current mode)
• Terminal Block: 18-point removable terminal block
• Current Consumption: 80 mA (from 5V internal bus)
• External Power: DC 24V (20.4–28.8V)
• Dimensions (W x H x D): 27.4 mm x 90 mm x 70 mm
• Weight: Approx. 120 g
• Operating Temperature: 0°C to +55°C

Features & Benefits

• Integrated HART communication — eliminates separate HART multiplexers and hand-held communicators, reducing hardware cost by 60% per loop
• Channel-to-channel isolation — galvanic isolation prevents ground loop errors when multiple HART devices share different ground potentials
• 16-bit resolution — 0.0015% measurement granularity enables precise process control for pressure, flow, and temperature loops
• Multi-variable HART data — read primary variable, secondary variable, and device status from smart transmitters in a single scan
• 250 ms per channel — 1-second total scan for all 4 channels meets the requirements of most slow process loops (level, temperature)

Typical Applications

• Smart pressure transmitter integration in oil & gas pipelines
• Coriolis flow meter HART data acquisition in chemical batching
• Multivariable temperature transmitter monitoring in HVAC central plants
• Valve positioner HART diagnostics in safety instrumented systems
• Remote device configuration without breaking the 4–20 mA loop
• Asset management system integration for predictive maintenance

Installation Guide

1. Verify HART device compatibility — confirm your field instruments support HART 5/6/7 and are configured for 4–20 mA + HART mode (not 4–20 mA only).
2. Install in I/O slot — mount the 2MLF-AC4H in any available ML200 I/O slot.
3. Connect 24V external power — wire DC 24V to the external power terminals for loop power supply.
4. Wire 4–20 mA loops — connect each HART device to the corresponding channel terminals (AI+, AI-, EXC). Use 2-wire or 4-wire configuration as per device manual.
5. Enable HART in SoftMaster — in the CPU I/O parameters, set each channel to HART mode and configure the HART polling address.
6. Verify communication — use the SoftMaster HART diagnostic screen to read device tag, manufacturer, and primary variable from each connected instrument.

FAQ

Q: What is the difference between 2MLF-AC4H and 2MLF-AC4A?
A: The 2MLF-AC4H includes integrated HART protocol communication. The 2MLF-AC4A is a standard 4–20 mA analog input without HART. Choose AC4H for smart HART instruments; choose AC4A for conventional 4–20 mA transmitters.

Q: Can I use this module with non-HART 4–20 mA devices?
A: Yes. The 2MLF-AC4H is backward compatible with standard 4–20 mA devices. HART functionality is optional — if no HART device is connected, the channel operates as a standard analog input.

Q: What is the maximum loop resistance?
A: The module supports loop resistances up to 600 Ω at 24V DC supply. For longer cable runs, use an external loop power supply or HART signal conditioner.

Q: Does this module provide loop power?
A: Yes. The 2MLF-AC4H provides internal 24V DC loop power for each channel. Alternatively, you can use an external 24V supply for isolated loop power.

Selection Tips

• Choose 2MLF-AC4H when your field instruments are HART-enabled smart transmitters (pressure, flow, temperature, level).
• For conventional 4–20 mA devices without HART, the 2MLF-AC4A is more cost-effective.
• For voltage input (0–10V, 1–5V), select 2MLF-AV8A (8-channel voltage input).
• Always verify your HART device polling address — each device on the same loop must have a unique HART address (1–15 for multidrop mode).
• Use shielded twisted-pair cable for HART loops to prevent electromagnetic interference from VFDs and contactors.