Name: 6ES7421-1FH20-0AA0 SIMATIC S7-400 DI Module | 120/230V AC/DC Inputs
SKU: 6ES7421-1FH20-0AA0
Price: 234.00 USD
Availability: InStock

Product details

Product Overview

Siemens 6ES7421-1FH20-0AA0 – digital input module for SIMATIC S7-400 systems
- Provides 16 isolated digital input channels
- Accepts 120/230V AC and DC signals (47-63 Hz)
- Complies with IEC 61131 Type 2 standards
- Ideal for high-voltage industrial environments

Technical Specifications

Brand & Model
- Brand: Siemens
- Model: 6ES7421-1FH20-0AA0
- Series: SIMATIC S7-400
- Product type: Digital input module SM 421
Input Characteristics
- Number of inputs: 16 channels
- Input type: AC/DC (universal voltage)
- Rated voltage: 120/230V UC
- Signal “0” range: 0 to 40V AC / -40 to +40V DC
- Signal “1” range: 74-264V AC / 80-264V DC
- Input delay (0→1): 20ms (AC) / 15ms (DC)
- Input delay (1→0): 30ms (AC) / 25ms (DC)
Current & Power
- Backplane current: max 80mA at 5V DC
- Typical input current: 10-14mA AC / 1.8-2mA DC
- Power loss: 12W typical
- Max quiescent current: 6mA AC / 2mA DC
Isolation & Protection
- Channel isolation: 500V AC tested
- Isolation between channels: Yes (in groups of 4)
- Isolation from backplane bus: Yes
- No built-in diagnostics function
Physical & Environmental
- Dimensions: 25mm x 290mm x 210mm
- Weight: 650g (1.43 lbs)
- LED status indicator: Green per channel
Wiring & Connectivity
- Cable length (shielded): 1000m max
- Cable length (unshielded): 600m max
- Supports 2-wire sensors (max 5mA quiescent)
- Encoder type: 2-wire sensors only

Expert Review

Field engineer’s insight: This module handles high-voltage AC/DC inputs reliably. Many plants use it for 230V motor starter feedback and 120V limit switches. The 600m unshielded cable length saves wiring costs in large factories.

Manager’s Insight

Why choose this module: The 6ES7421-1FH20-0AA0 reduces spare parts inventory. One module replaces both AC and DC input types. Its 16 channels in 25mm width save rack space.

Suitable Devices & Applications

Compatible systems: SIMATIC S7-400 (all CPUs)
Common applications:
- Motor starter feedback monitoring (230V AC)
- Limit switch and proximity sensor inputs
- Power distribution panel status signals
- Packaging machinery control systems

Installation Guide

Turn off all power to the S7-400 rack
Insert module into any available slot on the backplane
Secure with the locking mechanism
Wire input signals to the front connector (40-pin)
Connect shielded cables for runs over 600 meters
Ensure proper grounding for noise reduction

Maintenance & Debugging

Check green LED per channel for signal presence
No periodic calibration needed
Clean front connector annually in dusty environments
Use diagnostic tools via S7-400 CPU for troubleshooting

Package Contents

1x 6ES7421-1FH20-0AA0 digital input module
1x front connector (not pre-wired)
1x product documentation CD

Warranty & Shipping

12-month warranty against manufacturing defects
Ships within 12-24 hours on business days
Express delivery via FedEx, UPS, or DHL

Frequently Asked Questions (FAQ)

Q: Can I mix AC and DC sensors on the same module?
- A: Yes, each channel accepts both AC and DC signals independently.
Q: What happens if I apply 240V DC instead of AC?
- A: The module accepts 80-264V DC, so 240V DC works fine.
Q: Why does my input not turn on with a 24V sensor?
- A: The minimum ON voltage is 74V AC or 80V DC. 24V sensors need a different module (6ES7421-1BL00-0AA0).
Q: How many modules can I install in one rack?
- A: Up to 21 modules per S7-400 rack (depending on power supply capacity).
Q: Does this module support diagnostics in STEP 7?
- A: No, diagnostics function is not available on this module. Use the CPU diagnostic buffer for fault analysis.