Product Overview

The Honeywell 2MLI-D24B is a 32-point DC 24V Digital Input Module for the MasterLogic-200 PLC system. It collects discrete signals from field devices and transfers their status to the CPU, where they are evaluated as part of the programmed machine or process control logic.

This module uses a current source input configuration. That distinction is important when selecting field devices and planning the I/O wiring. Unlike the 2MLI-D24A, which supports both current source and sink input arrangements, the 2MLI-D24B is intended for source-type input connections.

With 32 input channels, the module can monitor several groups of industrial switching devices through one I/O position. Typical signals include proximity sensor outputs, limit switches, push buttons, relay contacts, and equipment status feedback. In a packaging line, for example, the module can collect product detection signals, machine position feedback, and guard-switch conditions for processing by the PLC CPU.

The input circuitry uses photocoupler isolation to separate external field signals from the internal electronic circuits. This is useful in control cabinets where multiple sensors and switching devices share the same installation environment.

Another practical feature is the adjustable input response time. Both OFF-to-ON and ON-to-OFF transitions can be configured through CPU parameters. Seven settings are available, ranging from 1 ms to 100 ms, with 3 ms as the default. Engineers can select the appropriate response setting according to the switching characteristics of connected devices and the requirements of the control sequence.

The 2MLI-D24B uses a 40-point connector for external signal connections. Its 32-channel configuration makes it suitable for larger discrete signal groups in automated machinery, production equipment, and industrial process installations.

Technical Specifications

Product Features

1. Thirty-Two DC 24V Input Channels

The 2MLI-D24B provides 32 digital input channels for acquiring discrete field signals. This channel capacity allows engineers to monitor multiple sensors, switches, and equipment feedback points without distributing the signals across several smaller input modules.

2. Current Source Input Configuration

The module uses a current source input arrangement. Field devices must be selected and wired according to this electrical configuration. This is particularly important when replacing a different MasterLogic-200 input module, since the D24B and D24A have different input circuit arrangements.

3. Photocoupler Isolation

Photocoupler isolation separates the external input signals from the internal PLC electronics. This helps limit the transfer of electrical disturbances from field wiring into the controller circuitry.

4. Adjustable Input Response Time

Both OFF-to-ON and ON-to-OFF transitions support seven selectable response-time settings: 1, 3, 5, 10, 20, 70, and 100 ms. The default is 3 ms, and the settings are configured through CPU parameters.

5. Individual Input Status Monitoring

Input ON status is indicated through LED operation. Maintenance personnel can use these indicators to check whether field devices are producing the expected switching signals during commissioning and troubleshooting.

6. Thirty-Two-Point Common Arrangement

The module uses a 32-point common configuration. The shared COM connection should be considered when preparing the field wiring and assigning input devices to the module.

7. Forty-Point Connector Interface

External wiring is connected through a 40-point connector. This interface accommodates the module’s 32 input channels and associated common and NC connections.

8. Industrial DC Signal Compatibility

The module operates with a rated input voltage of 24V DC and an operating range of 20.4–28.8V DC. It can therefore be incorporated into standard 24V DC industrial control circuits when the field device output characteristics are compatible.

Working Principle

The 2MLI-D24B receives discrete electrical signals from external DC 24V devices and converts their switching states into digital information for the MasterLogic-200 CPU.

When a connected sensor or switch changes state, its output circuit supplies an electrical signal to the corresponding input channel. The module evaluates the input voltage and current against the specified switching thresholds.

For an ON condition, the input signal must reach at least 19V DC and provide a current of 3 mA or higher. For an OFF condition, the voltage must be 11V DC or lower, with current at 1.7 mA or lower.

The signal then passes through the photocoupler isolation stage. Once the input state has been processed, the module transfers the digital status to the CPU through the MasterLogic-200 system backplane.

The CPU evaluates the input information against the application program. For example, when a sensor detects a component at an assembly station, the module reports the corresponding input state. The CPU checks this signal together with other operating conditions before allowing the next machine sequence to start.

The response-time configuration determines how long the module takes to recognize a signal transition. Shorter settings are useful for applications requiring faster signal recognition, while longer settings can be selected when the connected devices or operating conditions require additional input filtering.

Typical Signal Processing Path:

DC 24V Field Sensor → 40-Point Connector → Input Circuit → Photocoupler Isolation → MasterLogic-200 CPU → Program Logic

Example Machine Operation:

1. A proximity sensor detects a workpiece entering an automated station.
2. The sensor changes its DC 24V output state.
3. The corresponding 2MLI-D24B input channel detects the electrical signal.
4. The module updates its digital input information.
5. The MasterLogic-200 CPU evaluates the signal and checks related interlocks.
6. The CPU executes the next programmed machine operation through the output modules.

Role in MasterLogic-200 Control Architecture

Within the MasterLogic-200 PLC architecture, the 2MLI-D24B serves as a 32-channel interface for discrete field signals. It collects operating information from external devices and makes that information available to the CPU for program execution.

Its 32-point configuration is useful in installations with a relatively large number of switching signals. Instead of distributing every sensor group across several smaller modules, engineers can consolidate up to 32 compatible input signals through one module.

The current source input configuration determines how field devices must be connected. When planning a replacement or system expansion, engineers should verify the input wiring arrangement rather than selecting a module based only on its channel count and rated voltage.

The module operates alongside the MasterLogic-200 CPU, power supply, base units, and output modules. The CPU processes the incoming signals, while the output modules handle the corresponding commands to connected field equipment.

Industrial Applications

Installation and Maintenance

1. Verify the Module Model: Confirm that the installed module is 2MLI-D24B, a 32-point DC 24V current source input module.
2. Check Base Compatibility: Verify that the selected MasterLogic-200 base supports the intended module arrangement and that the PLC rack configuration matches the project.
3. Confirm Field Device Compatibility: Check that connected sensors and switches are suitable for the current source input configuration before making electrical connections.
4. Verify Input Voltage: Ensure that field signals remain within the specified operating range of 20.4–28.8V DC.
5. Check Input Thresholds: Confirm that ON signals meet the minimum voltage and current requirements and that OFF signals fall within the specified limits.
6. Inspect the 40-Point Connector: Check connector alignment, contact condition, and secure installation before applying power.
7. Use Appropriate Wiring: Follow the specified 0.3 mm² cable requirement and maintain clear separation between signal wiring and potential sources of electrical interference.
8. Check Common Connections: Verify the 32-point common arrangement and ensure that the COM wiring matches the module’s input configuration.
9. Configure Response Time: Select the OFF-to-ON and ON-to-OFF response settings through CPU parameters according to the requirements of the connected field devices.
10. Monitor Input Indicators: Activate individual field devices and confirm that the corresponding input ON LED responds correctly.
11. Verify PLC Address Mapping: Check that the 32 physical input channels correspond to the correct addresses and variables in the application program.
12. Maintain Wiring Documentation: Record field device assignments, connector pin information, input addresses, and response-time settings for future maintenance and troubleshooting.

Compatible System Components

Recommended Related Models

Key Advantages

• 32 DC 24V digital input channels.
• Current source input configuration.
• Photocoupler isolation between field and internal circuits.
• Seven selectable input response-time settings.
• Default input response time of 3 ms.
• Individual input ON LED indicators.
• 32-point common input arrangement.
• 40-point connector interface.
• Integration with the modular MasterLogic-200 PLC architecture.
• Suitable for multi-sensor machine monitoring and industrial discrete control.

Technical FAQs

What is the difference between the 2MLI-D24B and 2MLI-D24A?

Both modules provide 32 DC 24V digital input channels, but their input configurations are different. The 2MLI-D24A supports current source and sink input arrangements, while the 2MLI-D24B uses a current source input configuration. Field wiring compatibility should therefore be checked before replacing one with the other.

How many field devices can the 2MLI-D24B monitor?

The module provides 32 input points, allowing it to monitor up to 32 compatible discrete signals. The actual number of simultaneously active inputs must also account for the module’s input derating requirements, operating voltage, and ambient temperature conditions.

Can the response time be configured separately for input activation and deactivation?

Yes. Both OFF-to-ON and ON-to-OFF response times can be configured through CPU parameters. The available settings are 1, 3, 5, 10, 20, 70, and 100 ms, with 3 ms as the default setting.

What type of external connection does the 2MLI-D24B use?

The module uses a 40-point connector for external field wiring. Its 32 input channels are arranged with a shared common connection and additional NC contacts. The connector pin assignment should be checked against the module wiring diagram before installation or replacement.