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- HART Analog Output Module
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Product Overview
The Honeywell 2MLF-DC4H MasterLogic-200 HART Analog Output Module is a four-channel analog output module that converts digital values from a compatible MasterLogic-200 PLC into current signals for industrial field devices. In addition to conventional analog control, it supports HART (Highway Addressable Remote Transducer) communication, allowing digital information to be exchanged with compatible HART field instruments over the same wiring used for the analog current signal.
This combination is useful in process automation systems where the controller must regulate field equipment while maintaining access to instrument information. A PLC can send a 4–20 mA command to a compatible control valve or positioner while HART communication supports access to available device data and diagnostic information.
The 2MLF-DC4H supports both 4–20 mA and 0–20 mA output ranges, but HART communication is available only when the corresponding output is configured for 4–20 mA. Each channel can be configured for its required output range and digital data format through the PLC program or I/O parameters.
Unlike the 2MLF-DC4S, which is specified for isolation between output channels, the 2MLF-DC4H uses photocoupler isolation between the input terminal and PLC power, with no isolation between individual output channels. This distinction matters when selecting a module for installations with separate field circuits or specific isolation requirements.
For maintenance and system integration, engineers should verify the output range, HART communication requirements, digital scaling, field-device compatibility, and channel wiring before commissioning the module.
Technical Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | Honeywell |
| Product Type | HART Analog Output Module |
| Model | 2MLF-DC4H |
| Product Series | MasterLogic-200 |
| Module Type | Four-Channel HART Analog Output Module |
| Number of Output Channels | 4 |
| Analog Output Range | DC 4–20 mA, DC 0–20 mA |
| Maximum Load Resistance | 600 Ω |
| HART Communication | Supported with 4–20 mA output |
| HART Communication Mode | Single primary master |
| Maximum Resolution | 1/16,000 |
| Resolution at 4–20 mA | 1.0 μA |
| Resolution at 0–20 mA | 1.25 μA |
| Accuracy at 25°C | ±0.1% or less |
| Accuracy at 0–55°C | ±0.3% or less |
| Maximum Conversion Speed | 100 ms per 4 channels |
| Absolute Maximum Output | DC 24 mA |
| Digital Input Formats | Unsigned, Signed, Precise, Percentile |
| Isolation Method | Photocoupler isolation between input terminal and PLC power; no isolation between channels |
| Terminal Connection | 18-point terminal |
| I/O Points Occupied | Fixed type: 64 points; non-fixed type: 16 points |
| Internal Current Consumption | DC 5 V, 200 mA |
| External Current Consumption | DC 24 V, 220 mA |
| Dimensions | 113 × 27 × 98 mm |
| Weight | 0.15 kg |
Product Features
- Four-channel analog output: Provides four current-output channels for controlling compatible industrial field devices.
- HART communication support: Enables supported digital communication with compatible HART instruments through the analog signal wiring.
- Selectable current ranges: Supports 4–20 mA and 0–20 mA output configurations according to the application.
- High-resolution conversion: Provides a maximum resolution of 1/16,000 for the configured output range.
- Channel-specific configuration: Allows output ranges and digital data formats to be configured through the PLC program or I/O parameters.
- Multiple data formats: Supports unsigned, signed, precise, and percentile values to accommodate different control-program requirements.
- Defined load capability: Supports output circuits with a load resistance of up to 600 Ω.
- PLC power isolation: Uses photocoupler isolation between the input terminal and PLC power, while individual output channels are not isolated from one another.
- Field-instrument integration: Combines analog command transmission with HART communication for compatible process instruments.
Working Principle
The 2MLF-DC4H converts digital values generated by the MasterLogic-200 CPU into analog current signals. When configured for HART operation, it also supports digital communication with compatible field instruments through the same signal wiring.
The process begins when the PLC control program calculates a required output value. The module interprets that value according to the configured data format and output range, then generates the corresponding current signal. The receiving device uses this signal to regulate a process variable, such as flow, pressure, temperature, or valve position.
A typical analog control path is:
PLC Control Program → Digital Output Value → 2MLF-DC4H → 4–20 mA Signal → Field Actuator
When HART communication is enabled, digital information can be exchanged with a compatible instrument over the 4–20 mA loop. This can support access to available instrument variables, configuration information, and diagnostic data without requiring a separate communication cable.
HART communication is not supported when the output range is configured for 0–20 mA. Applications requiring HART must therefore use the 4–20 mA range and a compatible HART field device.
The module supports four digital data formats:
- Unsigned Value: 0–16000.
- Signed Value: -8000 to 8000.
- Precise Value: 4000–20000 for 4–20 mA, or 0–20000 for 0–20 mA.
- Percentile Value: 0–10000.
The selected data format determines how the PLC’s digital command corresponds to the analog output. Correct scaling is essential to avoid discrepancies between the requested process value and the current received by the field device.
The module’s isolation arrangement must also be considered during installation. Photocoupler isolation separates the input terminal from PLC power, but there is no isolation between output channels. Field wiring and grounding must account for this design characteristic.
Role in the MasterLogic-200 Control Architecture
The 2MLF-DC4H acts as the analog command and HART communication interface between the MasterLogic-200 PLC and compatible field instruments. It translates control-program values into current outputs while supporting digital communication with instruments configured for HART.
A typical process-control arrangement is:
Field Transmitters → PLC Input Modules → MasterLogic-200 CPU → 2MLF-DC4H → Control Valves and Other Field Devices
| System Component | Function |
|---|---|
| MasterLogic-200 CPU | Executes the control program and calculates output commands |
| 2MLF-DC4H | Generates four analog current outputs and supports HART communication |
| Analog Input Module | Receives process measurements from compatible transmitters |
| Digital Input Module | Receives discrete equipment status and interlock signals |
| HART Field Instrument | Exchanges analog process signals and supported digital information |
| Control Valve or Positioner | Uses the current command to regulate the process |
| PLC Base and Backplane | Provides the module mounting and system interconnection |
| Field Wiring | Carries current signals and HART communication |
| Engineering Software | Supports PLC programming, I/O configuration, and troubleshooting |
The module does not independently execute the complete process-control strategy. Its output depends on the PLC program, the configured signal range, the connected instrument, and the operating conditions of the field circuit.
Industrial Applications
| Application | Typical Use |
|---|---|
| Process Automation | Sending analog commands to compatible field instruments |
| Chemical Processing | Controlling modulating valves and monitoring HART-enabled instruments |
| Oil and Gas Facilities | Supporting analog control and instrument diagnostics |
| Water and Wastewater Treatment | Regulating flow-control equipment and compatible process actuators |
| Industrial Boilers | Controlling modulating equipment that accepts current references |
| Pharmaceutical Manufacturing | Supporting analog control of compatible process equipment |
| Food and Beverage Processing | Regulating process valves and other current-controlled devices |
| HVAC Process Control | Controlling compatible modulating actuators |
| Pressure Regulation | Sending current commands to suitable pressure-control equipment |
| Flow Control Systems | Adjusting valve position according to the PLC control strategy |
The 2MLF-DC4H is particularly relevant where analog control and HART instrument communication are both required. Applications that require electrical isolation between individual output channels should be evaluated carefully because this model does not provide channel-to-channel isolation.
Installation and Maintenance
- Verify the module identity: Confirm that the installed or replacement module is the Honeywell 2MLF-DC4H rather than another MasterLogic-200 analog output variant.
- Check the PLC configuration: Verify the CPU, base, module position, and I/O addressing against the system configuration.
- Select the correct output range: Configure each channel for 4–20 mA or 0–20 mA according to the connected field device.
- Confirm HART requirements: If digital instrument communication is required, ensure the corresponding channel uses the 4–20 mA output range and the field instrument supports HART.
- Verify load resistance: Check that the total output-loop load does not exceed the specified maximum of 600 Ω.
- Review digital scaling: Confirm the selected unsigned, signed, precise, or percentile data format and ensure that the PLC program uses the corresponding value range.
- Inspect terminal wiring: Check the 18-point terminal connections against the module wiring diagram before energizing the system.
- Account for channel isolation: Remember that the module does not provide isolation between individual output channels. Check the grounding and wiring arrangement for all connected circuits.
- Inspect the module installation: Ensure that the module is correctly seated and that the terminal connections and associated wiring are secure.
- Test analog output values: Use an appropriate measuring instrument to verify the current produced by each channel at representative commanded values.
- Verify HART communication: For channels configured for 4–20 mA, confirm communication with the compatible field instrument and check the available device information or diagnostic status.
- Document commissioning results: Record the output range, data format, I/O assignment, measured current, HART communication status, and any corrective actions.
Follow the applicable Honeywell installation and electrical safety procedures before removing or replacing the module. If the output is incorrect or HART communication fails, check the configuration, loop resistance, field wiring, instrument compatibility, and PLC program before concluding that the module is defective.
Compatible System Components
The 2MLF-DC4H is part of the Honeywell MasterLogic-200 modular I/O family. Related components support analog input, analog output, and discrete control functions within a compatible PLC configuration.
| Component | Function |
|---|---|
| Honeywell MasterLogic-200 CPU | Executes PLC logic and manages I/O data |
| Honeywell 2MLF-AC8A | Eight-channel analog current input module |
| Honeywell 2MLF-AV8A | Eight-channel analog voltage input module |
| Honeywell 2MLF-DC4A | Four-channel analog current output module |
| Honeywell 2MLF-DC4S | Four-channel current output module with isolation between output channels |
| Honeywell 2MLF-DC8A | Eight-channel analog current output module |
| Honeywell 2MLF-DV4A | Four-channel analog voltage output module |
| Compatible HART Field Instruments | Exchange supported digital data over compatible 4–20 mA loops |
| MasterLogic-200 PLC Base | Provides mounting and electrical interconnection for compatible modules |
| PLC Engineering Software | Supports programming, configuration, and diagnostics |
Recommended Related Models
| Model | Product Type | Relevance |
|---|---|---|
| Honeywell 2MLF-DC4A | MasterLogic-200 Analog Current Output Module | Four-channel current output for applications not requiring HART |
| Honeywell 2MLF-DC4S | MasterLogic-200 Isolated Analog Current Output Module | Four-channel current output with isolation between channels |
| Honeywell 2MLF-DC8A | MasterLogic-200 Analog Current Output Module | Eight-channel current output alternative |
| Honeywell 2MLF-DV4A | MasterLogic-200 Analog Voltage Output Module | Four-channel voltage output alternative |
| Honeywell 2MLF-AC4H | MasterLogic-200 HART Analog Current Input Module | Four-channel HART current input for compatible instruments |
| Honeywell 2MLF-AC8A | MasterLogic-200 Analog Current Input Module | Eight-channel analog current input for process measurements |
Key Advantages
- Combines four analog current outputs with HART communication support.
- Allows compatible instruments to exchange digital information over existing 4–20 mA signal wiring.
- Supports configurable output ranges and multiple digital data formats.
- Provides high-resolution current conversion for process-control applications.
- Integrates analog field-device control into the MasterLogic-200 PLC architecture.
- Supports maintenance and troubleshooting through available HART instrument information.
Technical FAQs
Can HART communication operate when a channel is configured for 0–20 mA?
No. HART communication is supported when the channel is configured for 4–20 mA. If HART access is required, select the 4–20 mA range and verify that the connected field instrument supports the protocol.
Does the 2MLF-DC4H isolate each output channel from the others?
No. The module provides photocoupler isolation between the input terminal and PLC power, but it does not provide isolation between individual output channels. This should be considered when connecting instruments with different grounding arrangements or separate electrical circuits.
What is the maximum load resistance for the analog output loop?
The specified maximum load resistance is 600 Ω. The complete loop load must remain within this limit for the module to deliver the required current output correctly.
Why might HART communication fail even when the analog current output is correct?
Check that the channel is configured for 4–20 mA, the field instrument supports HART, and the loop wiring and communication configuration are correct. Also verify the HART master arrangement, since the module documentation specifies single-primary-master operation.