Honeywell 2MLF-RD4A 4-Channel RTD Input Module

Product Overview

The Honeywell 2MLF-RD4A is a 4-channel RTD (Resistance Temperature Detector) input module for the MasterLogic-200 (ML200) PLC system. It directly interfaces with Pt100, Pt1000, Cu50, and Cu100 RTD sensors, providing high-accuracy temperature measurement for process control, HVAC, and machine monitoring applications. With 16-bit resolution and built-in lead-wire compensation, it eliminates the need for external signal conditioners, reducing panel complexity and installation cost.

Key Specifications

• Product Type: 4-Channel RTD Input Module
• Series: MasterLogic-200 / ML200
• Input Channels: 4
• Sensor Types: Pt100, Pt1000, Cu50, Cu100 (3-wire or 4-wire)
• Measurement Range: -200°C to +850°C (Pt100)
• Resolution: 16-bit (0.1°C typical)
• Accuracy: ±0.1% FS at 25°C
• Conversion Speed: 80 ms / 4 channels
• Isolation: Channel-to-channel and channel-to-logic isolation
• Lead-Wire Compensation: Automatic 3-wire and 4-wire compensation
• External Connection: 20-point removable terminal block
• Current Consumption: 50 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. 100 g
• Operating Temperature: 0°C to +55°C

Features & Benefits

• Direct RTD interface — eliminates external transmitters and signal conditioners, reducing panel component count by 60% per temperature loop
• Automatic lead-wire compensation — 3-wire and 4-wire RTD support automatically nullifies cable resistance errors, ensuring ±0.1% accuracy even with long sensor cables
• Wide -200°C to +850°C range — covers cryogenic, ambient, and high-temperature process applications with a single module type
• 16-bit resolution — 0.1°C measurement granularity enables precise temperature control for pharmaceutical and food-grade batch processes
• Channel isolation — prevents ground loop errors when multiple RTDs are installed on different grounded vessels or pipes

Typical Applications

• Reactor jacket temperature monitoring in chemical plants
• Boiler steam temperature measurement in power generation
• HVAC chilled water and hot water supply temperature
• Food & beverage pasteurization and CIP temperature verification
• Pharmaceutical autoclave and freeze-dryer temperature control
• Motor bearing and gearbox oil temperature monitoring

Installation Guide

1. Verify RTD type — confirm your sensors are Pt100, Pt1000, Cu50, or Cu100 and wired as 3-wire or 4-wire configuration.
2. Install in I/O slot — mount the 2MLF-RD4A in any available ML200 I/O slot.
3. Connect 24V external power — wire DC 24V to the external power terminals for the excitation circuits.
4. Wire RTD sensors — connect sensor leads to the appropriate terminals:
   • 3-wire: Connect one lead to AI+, one to AI-, and the compensation lead to the EXC terminal.
   • 4-wire: Connect two leads to AI+ and AI- (current injection), and two leads to S+ and S- (sense).
5. Configure sensor type in SoftMaster — select Pt100, Pt1000, Cu50, or Cu100 and the wiring method (3-wire or 4-wire) in the CPU I/O parameters.
6. Verify temperature reading — compare the PLC reading against a calibrated handheld thermometer at a known temperature point (e.g., ice bath at 0°C).

FAQ

Q: What is the difference between 2MLF-RD4A and 2MLF-RD8A?
A: The 2MLF-RD4A provides 4 RTD channels. The 2MLF-RD8A provides 8 RTD channels in the same footprint. Choose RD8A for high-density temperature monitoring; choose RD4A when 4 channels are sufficient and lower cost is preferred.

Q: Can I use thermocouples with this module?
A: No. The 2MLF-RD4A is for RTD sensors only. For thermocouples (J, K, T, E, R, S, B types), use the 2MLF-TC4S (4-channel isolated thermocouple input) module.

Q: What is the maximum cable length from sensor to module?
A: With 3-wire or 4-wire compensation, cable runs up to 500 meters are possible using 1.0 mm² or larger copper cable, depending on environmental noise.

Q: Does this module provide sensor excitation?
A: Yes. The 2MLF-RD4A provides constant current excitation to the RTD. No external excitation source is required.

Selection Tips

• Choose 2MLF-RD4A for 4-channel RTD temperature measurement in standard process applications.
• If you need 8 channels in the same slot, upgrade to 2MLF-RD8A.
• For thermocouple applications (high temperature >850°C), select 2MLF-TC4S instead.
• Always use shielded, twisted-pair cable for RTD wiring to minimize electromagnetic interference.
• Verify your RTD wiring configuration (3-wire vs. 4-wire) before ordering cable — 4-wire provides the highest accuracy but requires more conductors.