Siemens Simatic S7-400, Digital input SM 421, 24 - 60V

Product Overview

The SIMATIC S7-400 digital input module SM 421 provides 16 isolated digital inputs for connecting field devices to the S7-400 controller. This module features UC 24-60 V operation with integrated alarm and diagnostic capabilities for enhanced system monitoring. Designed for industrial automation applications requiring reliable digital signal acquisition from sensors, switches, and proximity detectors.

Key Features

• Universal Voltage Operation: Supports UC 24-60 V input voltage range for both AC and DC applications, providing flexibility in field device connections
• Optical Isolation: Features optically isolated inputs to prevent ground loops and enhance electrical safety between field devices and controller
• Alarm Capabilities: Integrated alarm functions provide real-time notification of input status changes and system events
• Diagnostic Functions: Advanced diagnostic capabilities enable proactive maintenance and system troubleshooting
• High Input Density: 16 digital inputs in a compact module design maximize I/O density in the control cabinet
• Hot-Swappable Design: Supports module replacement during operation without system shutdown, minimizing downtime

Technical Specifications

• Input Configuration: 16 isolated digital inputs
• Input Voltage Range: UC 24-60 V (AC/DC universal)
• Input Current: Typical 4-10 mA for "1" signal
• Maximum Input Current: 0.5-2 mA for "0" signal
• Input Delay: Configurable input delay settings for channel groups
• Cable Length: Up to 100 m unshielded (0.5 ms delay), up to 600 m unshielded (3 ms delay), up to 1000 m shielded
• Isolation: Optical isolation between inputs and logic
• Connection Type: Front connector with screw/spring clamp terminals
• Net Weight: 0.790 kg
• Physical Dimensions: 290 mm (H) x 25 mm (W) x 210 mm (D)
• Packaging Dimensions: 23.30 x 30.20 x 4.10 cm
• Country of Origin: Germany
• EAN: 4025515128922
• UPC: 662643186284

Compliance & Certifications

• RoHS Compliance: Compliant with RoHS directive since March 1, 2008
• WEEE Compliance: Subject to WEEE take-back obligations
• Export Control: AL: N / ECCN: N
• Industrial Standards: Designed for industrial automation applications
• Safety Standards: Meets relevant safety standards for industrial control systems

REACH Regulation Information

• This product contains substances from the REACH candidate list in concentrations higher than 0.1% w/w:
  • Lead
  • Lead monoxide (lead oxide)
  • Tris(4-nonylphenyl, branched and linear) phosphite (TNPP)
• These substances are considered safe when used as intended according to product documentation

Product Lifecycle

• Status: PM300 Active Product
• Phase-out Notice: Product phase-out scheduled since October 1, 2025

Input Characteristics

• Signal Types: Compatible with standard switches and 2-wire proximity switches (BERO)
• Input Characteristic: Complies with IEC 61131-2 standards
• Signal Recognition: Configurable for different input delay settings
• Wire Break Detection: Supports wire break monitoring for enhanced diagnostics
• Status Display: Green LED per channel for visual status indication

Applications

• Industrial process control systems requiring universal voltage inputs
• Manufacturing automation with mixed AC/DC sensor signals
• Machine control applications with proximity switches and limit switches
• Safety systems requiring diagnostic and alarm capabilities
• Systems with extended cable runs requiring signal integrity
• Applications requiring hot-swappable I/O modules for minimal downtime

System Integration

• Controller Compatibility: Designed specifically for SIMATIC S7-400 automation systems
• PROFIBUS DP Support: Compatible with PROFIBUS DP distributed I/O configurations
• Centralized/Distributed Operation: Supports both centralized and distributed I/O architectures
• Modular Design: Integrates seamlessly with other S7-400 signal modules and system components

Diagnostic Features

• Real-time Monitoring: Continuous monitoring of input status and module health
• Alarm Generation: Automatic alarm generation for input status changes
• Error Detection: Detection of wire breaks, short circuits, and other fault conditions
• Status Reporting: Comprehensive status reporting through STEP 7 programming software
• Preventive Maintenance: Diagnostic data supports predictive maintenance strategies

Installation & Configuration

• Easy Installation: Standard S7-400 module mounting with secure mechanical connection
• Front Connector System: Uses front connector for simplified wiring and maintenance
• Parameter Assignment: Configurable input delays and diagnostic settings
• Channel Grouping: Input delay settings applied to channel groups (0-7 and 8-15)
• Hot-Swap Capability: Module replacement during operation without system interruption

Download existing graphical data for this product:

• Product Datasheet
• Technical Documentation
• S7-400 Reference Manual
• Product Support Page