Siemens 6ES5421-5AA11 Input Module | 16-Point 120V AC 0.47kg

Technical Specifications and Input Design

This digital input module interfaces with 120V AC field devices for SIMATIC S5 systems. The Siemens 6ES5421-5AA11 reads signals from limit switches, pushbuttons, and proximity sensors. You can install this unit into any standard S5-115U or S5-135U rack slot. Its rugged design withstands high-voltage transients from industrial machinery. The module weighs approximately 0.47 kilograms. Its dimensions measure 25 cm in height, 5 cm in width, and 21 cm in depth.

Parameter	Specification
Brand	Siemens
Model	6ES5421-5AA11
Category	Digital Input Module / AC Discrete Input Unit
Weight	0.47 kg
Height	25 cm
Width	5 cm (single slot)
Depth	21 cm
Number of Inputs	16 points
Input Voltage Range	85-132V AC (47-63 Hz)
Input Type	AC optocoupler isolated
Input Current per Point	10 mA typical at 120V AC
Minimum ON Voltage	74V AC
Maximum OFF Voltage	40V AC
Response Time (ON to OFF)	25 milliseconds maximum
Response Time (OFF to ON)	25 milliseconds maximum
Isolation Voltage	2500V AC between field and logic
Energy Storage	None (no battery or capacitors)
Component Count	Single PCB with 16 optocoupler and filter circuits

Wiring and Group Configuration

The module divides its sixteen inputs into two isolated groups of eight. Each group shares a common AC return terminal for wiring convenience. You can connect different AC phases to each group safely. The Siemens 6ES5421-5AA11 uses a front-panel screw terminal strip. This terminal strip accepts wire sizes from 0.2 to 2.5 square millimeters. Each input point includes a green LED status indicator. This LED lights when the input detects a valid AC signal level.

Signal Processing and Noise Filtering

The input circuits include built-in filtering for 50/60 Hz AC line noise. Each channel requires at least 74V AC to register an ON condition reliably. The module uses an optocoupler for complete electrical isolation from the backplane. Consequently, the logic circuits remain safe from high-voltage field faults. The inputs respond within 25 milliseconds to any voltage change. This response time filters out short-duration line transients effectively. The module operates perfectly with standard 120V AC control transformers.

Installation and Operational Guidelines

You must insert this module into any standard S5 I/O rack slot. The backplane supplies 5V DC power to the optocoupler circuits. The module draws approximately 150 mA from this backplane supply. It stores no input states when you remove system power. Therefore, the CPU receives fresh input data after each power-up cycle. You should verify the applied voltage stays below 132V AC. Exceeding this limit will permanently damage the input circuits. The module requires no external power supply for normal operation.