The SM 1221 (6ES7 221-1BH32-0XB0) is a compact, high-density digital input expansion module designed for seamless integration with SIMATIC S7-1200 PLCs. Featuring 16 digital inputs (24 V DC), configurable sink/source logic, and high reliability in a small form factor, this module empowers precise and scalable industrial control applications.
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Key Technical Specifications
Specification Detail
Inputs 16 digital inputs, 24 V DC, sink/source configuration
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Supply Voltage 24 V DC rated; operating range: 20.4–28.8 V DC
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Backplane Load Powered via S7-1200 backplane bus (5 V DC max. 130 mA)
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Power Loss Approximately 2.5 W
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Input Characteristics Logic “0”: ≤ 5 V DC at 1 mA / Logic “1”: ≥ 15 V DC at ~4 mA; parameterizable input delay (0.2 ms to 12.8 ms)
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Cable Length Up to 500 m (shielded); 300 m (unshielded)
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Diagnostics & Indicators Input diagnostics with status LEDs
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Isolation & Protection IP20 housing; approvals: CE, UL/cULus, CSA, FM, RCM, KC, Marine
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Environmental Operating temp: –20 °C to +60 °C; storage: –40 °C to +70 °C; humidity: up to 95 % non-condensing
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Mechanical Dimensions: 45 × 100 × 75 mm (W × H × D); Weight: ~210 g
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Siemens Support

Lifecycle Active product (PM300); ships ex-works in 1 day; RoHS compliant since 15 March 2013
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Compliance Contains lead, lead monoxide, and BPA above 0.1% w/w per REACH Art. 33; no expected hazard under normal use
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Engineering Highlights

Dense I/O Integration
Adds 16 high-density digital inputs in a slim 45 mm module—ideal for compact installation.

Flexible Signal Handling
Sink/source configuration accommodates diverse wiring setups and industrial sensor types.

Tunable Response Time
Optional input delays (0.2–12.8 ms) help mitigate false triggering from signal noise or bouncing.

Extended Run Capability
Supports long cable runs—up to 500 m with shielded cable—a plus in distributed plant architectures.

Clear Operational Feedback
Input status LEDs and onboard diagnostics simplify system troubleshooting.

Rugged & Certified
Built to industrial standards with a robust temperature and humidity tolerance, backed by extensive safety certifications.

Compact, Lightweight Build
At just ~210 g and standard dimensions, it provides efficient system expansion without space penalty.

Ideal Use Cases

Enhancing discrete sensing capability in automation panels without enlarging control enclosures.

Deployments in environments with high electromagnetic interference or long wiring runs.

Applications requiring adjustable input timing to fine-tune system responsiveness.

Integrations requiring compliance with stringent industrial and safety standards.

Summary

The SIMATIC SM 1221 (6ES7 221-1BH32-0XB0) is a robust, compact digital input module that delivers high-density capabilities and flexible signal configuration to S7-1200 PLC systems. With comprehensive diagnostics, adaptable input behavior, and certifications for demanding environments, it’s engineered for precision, reliability, and scalable automation design.