Introduction

The Honeywell 2MLI-D21A Digital Input Module is an eight-point, 24 V DC input module for the MasterLogic-200 PLC platform. It collects discrete field signals from devices such as switches and control contacts, allowing the PLC to monitor equipment status and execute programmed control sequences.

The module features photo-coupler isolation, configurable input response times, and LED input status indication. Its source/sink input configuration supports suitable industrial digital signal applications when wired according to the manufacturer's requirements.

For maintenance engineers and system integrators, the 2MLI-D21A offers a dedicated digital input solution for compatible MasterLogic-200 installations. Verify the controller configuration, field wiring, and operating voltage before installation or replacement.

Technical Specifications

Parameter	Specification
Brand	Honeywell
Model	2MLI-D21A
Product Type	Digital Input Module
PLC Series	MasterLogic-200
Number of Input Points	8
Input Type	DC digital input, source/sink
Rated Input Voltage	24 V DC
Operating Voltage Range	20.4–28.8 V DC
Rated Input Current	Approximately 4 mA
Input Resistance	Approximately 5.6 kΩ
ON-State Threshold	19 V DC or higher / 3 mA or higher
OFF-State Threshold	11 V DC or lower / 1.7 mA or lower
Response Time	Configurable: 1, 3, 5, 10, 20, 70, or 100 ms
Default Response Time	3 ms
Isolation Method	Photo-coupler
Isolation Voltage	AC 560 V RMS / 3 cycles
Current Consumption	20 mA
Status Indication	Input ON LED
External Connection	9-point terminal block, M3 × 6 screw
Dimensions	120 × 25 × 110 mm
Weight	0.10 kg / 0.22 lb

Recommended Related Models

Honeywell 2MLI-D22A Digital Input Module — A 16-point, 24 V DC digital input module for applications requiring more input channels.
Honeywell 2MLI-D24A Digital Input Module — A 32-point, 24 V DC input option for higher channel density.
Honeywell 2MLI-D22B Digital Input Module — A 16-point, 24 V DC source-type input module.
Honeywell 2MLQ-RY2A Digital Output Module — For compatible relay-output control applications.
Honeywell 2MLQ-TR4A Digital Output Module — For compatible transistor-output applications.

Popular Related Models

Model	Product Description
Honeywell 2MLI-D21A	8-Point 24 V DC Digital Input Module
Honeywell 2MLI-D22A	16-Point 24 V DC Digital Input Module
Honeywell 2MLI-D22B	16-Point 24 V DC Source-Type Input Module
Honeywell 2MLI-D24A	32-Point 24 V DC Digital Input Module
Honeywell 2MLQ-RY2A	Relay Digital Output Module
Honeywell 2MLQ-TR4A	Transistor Digital Output Module

Applications

The Honeywell 2MLI-D21A Digital Input Module is an 8-point, 24 V DC input module designed for the MasterLogic-200 PLC system. It receives discrete signals from field devices and transfers their status to the PLC for logic processing, equipment monitoring, and automated control.

With source/sink input capability and photo-coupler isolation, the module is suitable for a range of industrial applications involving digital status signals.

Typical applications include:

Machine automation: Monitoring push buttons, limit switches, and other discrete control signals.
Production lines: Collecting equipment status and interlock signals for PLC logic.
Process monitoring: Detecting the on/off states of compatible field devices.
Industrial equipment control: Providing input feedback for automated sequences and operational checks.
System maintenance: Replacing a compatible digital input module in an existing MasterLogic-200 installation.

Advantages

Eight digital input points: Collects multiple discrete signals through a single module.
24 V DC input: Designed for common industrial control signal applications.
Source/sink compatibility: Supports the specified source/sink input configuration.
Photo-coupler isolation: Helps electrically isolate field input signals from internal circuitry.
Configurable response time: Input response can be selected through CPU parameters.
LED status indication: Provides visual indication when an input is active.
Compact form factor: Fits into compatible MasterLogic-200 modular control systems.

Technical FAQs

Q1: What is the Honeywell 2MLI-D21A used for?

The 2MLI-D21A receives discrete 24 V DC signals from field devices and provides their status to a compatible MasterLogic-200 PLC.

Q2: How many digital input points does it support?

The module supports eight digital input points, with a common connection for the group.

Q3: What is the rated input voltage?

Its rated input voltage is 24 V DC, with a documented operating range of 20.4–28.8 V DC, provided the specified ripple limit is met.

Q4: Does the module support source and sink inputs?

Yes. The 2MLI-D21A is specified as a source/sink-type digital input module. Check the field device wiring and PLC documentation to ensure the connection method is appropriate.

Q5: What is the rated input current?

The rated input current is approximately 4 mA per input point.

Q6: What is the input response time?

The response time can be configured to 1, 3, 5, 10, 20, 70, or 100 ms through CPU parameters. The default setting is 3 ms for both OFF-to-ON and ON-to-OFF transitions.

Q7: Does the module provide electrical isolation?

Yes. It uses photo-coupler isolation. The documented isolation voltage is AC 560 V RMS for three cycles under the specified test conditions.

Q8: How can an operator identify an active input?

The module includes input status LEDs. An input's LED illuminates when that input is ON.

Q9: What should be checked if an input signal is not detected?

Check the field device, 24 V DC supply, polarity, common wiring, terminal connections, and input status LED. Also verify the configured response time and confirm that the signal meets the module's ON-state requirements.

Q10: Which related modules can be considered when more input points are required?

The Honeywell 2MLI-D22A provides 16 digital input points, while the 2MLI-D24A provides 32. Confirm wiring, input type, base compatibility, and system configuration before selecting an alternative.

Look forward to your comments!Comment