Siemens 6ES7421-1FH20-0AA0 Input Module

This digital input module acquires 120 VAC signals from field devices for the SIMATIC S7-400 automation system. It monitors pushbuttons, limit switches, and proximity sensors in industrial control applications. The module’s high-density design provides 16 channels in a single slot of the S7-400 rack.

Input Configuration and Electrical Specifications

The Siemens 6ES7421-1FH20-0AA0 features 16 digital inputs, each with a nominal voltage of 120 VAC. Each channel delivers a typical input current of 10 mA and includes surge suppression. The module provides a galvanic isolation of 1500 VAC between the input and the backplane. It draws a typical current of 25 mA from the 24 VDC power supply. The module also consumes 250 mA from the internal 5 VDC backplane bus.

Technical Specifications

Specification	Detail
Model	6ES7421-1FH20-0AA0
Product Type	Digital Input Module
System Compatibility	SIMATIC S7-400
Number of Inputs	16
Nominal Voltage	120 VAC
Input Current per Channel	10 mA (typical)
Input Delay (Off to On)	10 ms
Input Delay (On to Off)	10 ms
Galvanic Isolation	1500 VAC
Power Consumption (5V)	250 mA
Power Consumption (24V)	25 mA
Dimensions	25 × 290 × 210 mm
Weight	0.8 kg
Operating Temperature	0°C to +60°C
Storage Temperature	-40°C to +85°C
Humidity	5% to 95% non-condensing
Certifications	CE, UL

Diagnostics and Protection Features

The module includes diagnostics for each channel to detect open-circuit and short-circuit conditions. It sends diagnostic messages to the CPU for alarm handling and maintenance alerts. The module also supports hardware interrupts for immediate fault response. A surge suppression circuit protects the inputs from voltage spikes. LED indicators display the status of each input and the overall module health.

System Integration and Application Use

This module integrates seamlessly into the S7-400 backplane bus for high-speed data exchange. It reads inputs cyclically from the field and provides the data to the CPU’s process image. Typical applications include motor control, valve monitoring, and status indication. The module’s built-in diagnostics minimize troubleshooting time in complex process plants. Chemical plants, refineries, and power stations benefit from its reliability.