SIEMENS 6ES7221-1BH22-0XA0 – 16-Point 24VDC Digital Input Module | SIMATIC S7-200
Engineering Background
The SIEMENS 6ES7221-1BH22-0XA0 is a compact digital input expansion module designed for the SIMATIC S7-200 Micro PLC platform — one of the most widely deployed small-scale automation controllers in industrial history. Engineered in Germany to IEC 61131-2 standards, this module extends the native I/O capacity of S7-200 CPUs, enabling precise acquisition of 16 discrete 24V DC field signals with high noise immunity and deterministic scan-cycle performance.
Product Positioning
Targeted at OEM machine builders, system integrators, and MRO procurement engineers who require a drop-in replacement or capacity expansion for existing S7-200 installations. The 6ES7221-1BH22-0XA0 is the standard 16-point DI variant in the EM 221 expansion family, offering the optimal balance of channel density, form factor, and cost-per-point for discrete sensing applications.
Complete Technical Specifications
| Parameter | Value |
|---|---|
| Part Number / SKU | 6ES7221-1BH22-0XA0 |
| Product Family | SIMATIC S7-200 EM 221 |
| Module Type | Digital Input Expansion Module |
| Number of DI Channels | 16 × 24V DC |
| Input Voltage (Rated) | 24V DC |
| Input Voltage Range | 20.4 – 28.8V DC |
| Logic 1 Signal Level | ≥ 15V DC (4 mA) |
| Logic 0 Signal Level | ≤ 5V DC (1 mA) |
| Input Impedance | 4 kΩ |
| Isolation | Optical (500V AC, 1 min) |
| Input Delay (Filter) | 0.2 ms / 6.4 ms (selectable) |
| Backplane Bus Current (5V DC) | 30 mA |
| Current Consumption (24V DC) | 4 mA per input (max) |
| Power Dissipation | 2 W (max) |
| Dimensions (W × H × D) | 71.2 × 80 × 62 mm |
| Weight | Approx. 170 g |
| Operating Temperature | 0 – 55 °C |
| Storage Temperature | -40 – 70 °C |
| Relative Humidity | 5 – 95% (non-condensing) |
| Protection Class | IP20 |
| Certifications | CE, UL, cUL, FM, ATEX (Zone 2) |
| Compatible CPUs | S7-200: CPU 221, 222, 224, 224XP, 226 |
| Country of Origin | Germany |
| MLFB / Order Number | 6ES7221-1BH22-0XA0 |
Proven Application Environments
- Discrete Manufacturing: Conveyor line end-of-travel sensing, part-present detection, and machine guarding interlocks.
- Building Automation: HVAC damper position feedback, door/window contact monitoring, and alarm panel integration.
- Water & Wastewater: Pump run/fault status acquisition, level switch monitoring, and valve position feedback.
- Food & Beverage: Packaging line sensor arrays, fill-level detection, and conveyor jam sensing.
- Energy & Utilities: Substation auxiliary contact monitoring and generator status acquisition.
- MRO / Retrofit: Direct drop-in replacement for failed EM 221 modules in legacy S7-200 installations without CPU reprogramming.
Engineering Advantages
- Optical Isolation: 500V AC galvanic isolation between field wiring and backplane bus eliminates ground-loop interference and protects the CPU from field-side transients.
- Selectable Input Filter: 0.2 ms fast filter for high-speed counting applications; 6.4 ms standard filter for noise-prone industrial environments — configurable per channel group in STEP 7-Micro/WIN.
- Plug-and-Play Expansion: Connects directly to the S7-200 CPU expansion port via integrated ribbon cable; no additional power supply or rack required for modules ≤ 4 in chain.
- LED Status Indication: Per-channel green LED provides real-time field signal status for rapid commissioning and fault diagnosis without a programming device.
- Compact DIN-Rail Form Factor: 71.2 mm width fits standard 35 mm DIN rail; side-by-side mounting with CPU and other EM modules minimizes panel footprint.
- Wide Temperature Range: 0–55 °C operating range supports installation in non-climate-controlled enclosures and outdoor cabinets with appropriate IP-rated housing.
System Architecture & Signal Flow
The 6ES7221-1BH22-0XA0 connects to the S7-200 CPU via the right-side expansion port using the integrated 10-pin ribbon cable. Field 24V DC signals are wired to the M1 and M2 terminal blocks (8 channels per group). Each input passes through an RC input filter (0.2 ms or 6.4 ms), then through an optocoupler stage providing 500V AC isolation before presenting a logic-level signal to the backplane bus. The CPU reads all 16 inputs within a single scan cycle via the I-memory image table (I0.0–I1.7 or mapped per CPU configuration). The module draws 30 mA from the 5V DC backplane bus and requires a 24V DC field supply (customer-provided or from CPU 24V sensor supply, subject to current budget).
Sourcing & Quality Verification
- Authentic Origin: All units sourced through verified industrial distribution channels with full traceability to authorized SIEMENS distributors.
- Incoming Inspection: Each module undergoes visual inspection, label verification (MLFB, date code, country of origin), and functional power-on test prior to dispatch.
- Packaging Integrity: Shipped in original or equivalent ESD-safe packaging with desiccant; outer carton includes tamper-evident sealing.
- Documentation: Certificate of conformity and test report available upon request for regulated industries (pharma, energy, defense).
- Warranty: 12-month warranty against manufacturing defects; DOA replacement within 7 business days.
Procurement Process
- Confirm Compatibility: Verify your S7-200 CPU model and current expansion module count (max 7 EM modules per CPU, subject to I/O and power budget).
- Request Quote: Contact [email protected] for volume pricing, lead time confirmation, and freight options.
- Place Order: Add to cart and complete checkout, or submit a purchase order via email for NET-30 qualified accounts.
- Shipping: Standard dispatch within 1–3 business days; DHL/FedEx express available for urgent requirements.
- After-Sales: Technical support available via email and phone for installation, configuration, and commissioning queries.
Technical FAQ
Q: Is the 6ES7221-1BH22-0XA0 compatible with S7-200 SMART CPUs?
A: No. The EM 221 series is designed exclusively for the classic S7-200 platform. S7-200 SMART uses a different expansion bus and requires SMART EM modules (e.g., 6ES7222-1BH22-0XA8).
Q: Can I use the module’s 24V DC sensor supply from the CPU?
A: Yes, if the CPU’s 24V DC sensor supply current budget permits. The 6ES7221-1BH22-0XA0 draws up to 4 mA per active input (64 mA max at full load). Verify against your CPU’s sensor supply specification.
Q: How many EM 221 modules can I chain to one CPU?
A: Up to 7 expansion modules total (any mix of EM types), subject to the CPU’s 5V DC backplane bus current limit (typically 660–1000 mA depending on CPU model).
Q: What programming software is required?
A: STEP 7-Micro/WIN V4.0 SP9 or later (for classic S7-200). No additional hardware configuration is required — the CPU auto-detects connected EM modules at power-up.
Q: Is the module available with ATEX certification for hazardous areas?
A: The standard 6ES7221-1BH22-0XA0 carries ATEX Zone 2 certification. For Zone 1/Zone 0 applications, Zener barrier or galvanic isolator interfaces are required in the field wiring.
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