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        • Lifecycle Status

          Discontinued / Obsolete by OEM
          Apter Power maintains a robust inventory of discontinued Siemens automation hardware, delivering thoroughly tested legacy modules to protect your plant from unexpected downtime.

        6ES7421-1BL01-0AA0

        / 4.9
        1001 reviews ｜ Need a Specific Revision?
        The 6ES7421-1BL01-0AA0 is a Siemens SIMATIC S7-400 SM 421 digital input module with 32 channels, 24V DC, optically isolated, 20 mA backplane current.
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        Warranty Policy
        We provide 1 year warranty for all remaining parts.
        The warranty period is one year from the date of shipment, unless otherwise stated in the parts description. We guarantee that the project will not exhibit functional defects that may occur under normal operating conditions during the warranty period.
        Return Notice
        The warranty period is one year from the date of shipment, unless otherwise stated in the parts description. We guarantee that the project will not exhibit functional defects that may occur under normal operating conditions during the warranty period.
        In the event of a defect, we will send new equipment, repair equipment or refund the purchase price based on our availability. You must contact us to obtain a return authorization and return the defective device to us within 14 days of reporting the defect.
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        Apter Power offers a wide range of components, products and services related to industrial automation. We also supply new products from a variety of quality manufacturers.
        How to order
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        Technical specifications for 6ES7421-1BL01-0AA0

        • Manufacturer:
          Siemens
        • Part Number:
          6ES7421-1BL01-0AA0
        • Product Family:
          Siemens Simatic S7-400
        • Product Type:
          Digital Input Module
        • Stock:
          1
        • Number of Inputs:
          32
        • Rated Input Voltage:
          24V DC
        • Signal:
          13V to 30V DC
        • Signal:
          7 mA
        • Max Permissible Quiescent Current (signal:
          1.3 mA
        • Input Delay (0→1):
          1.2 ms ... 4.8 ms
        • Current Consumption (5V backplane):
          max. 20 mA
        • Power Loss (typ.):
          6 W
        • Isolation Groups:
          32 channels as one group
        • Weight:
          0.6 kg
        • Estimated shipping dimensions:
          23x22.3x28.8cm
        • Tariff Code:
          8517795000
        • Country of origin:
          Germany
        • Place of shipment:
          Xiamen, Fujian, China
        By purchasing this item, you agree to the Terms & Conditions, ApterPower is not an authorized distributor for listed manufacturers or tradenames and therefore the manufacturer's warranty does not apply. All our products come with ApterPower's 1-year warranty.

        More Information

        Overview Manuals Specifications Application Performance & Efficiency Application Scenarios

        Features:

        • 32 channels in a 25 mm wide module; 24V DC; configurable input delay (1.2‑4.8 ms); 7 mA typical input current.
        • Minimizes load on the S7-400 rack power supply; allows more modules per rack.
        • Shielded cable up to 1000 m; unshielded up to 600 m; isolation between inputs and backplane (500V DC test); protection against field wiring faults.
        The 6ES7421-1BL01-0AA0 packs 32 digital input channels into a module just 25 mm wide. For a typical S7-400 system, this high density is a significant advantage when many digital inputs are required. Instead of using multiple 16‑channel modules consuming two or more slots, a single SM 421 handles 32 field devices – pushbuttons, limit switches, proximity sensors, or relay contacts. Each input operates at 24V DC with a typical current of 7 mA. The input delay is configurable from 1.2 to 4.8 ms, allowing engineers to balance response speed against noise immunity.

        S7-400 racks have a limited 5V power budget. Adding many I/O modules can quickly exceed the capacity of the power supply, forcing engineers to add expensive power supply modules or reduce I/O count. The 6ES7421-1BL01-0AA0 addresses this by drawing only 20 mA maximum from the 5V backplane bus. For comparison, some other 32‑channel input modules draw 100‑150 mA. With this module, an engineer can install five modules (160 inputs) using only 100 mA of 5V current – leaving ample capacity for other modules like analog inputs, outputs, or communication processors. The low power consumption also reduces heat dissipation in the rack.

        Field devices such as limit switches and proximity sensors are often located hundreds of meters from the PLC cabinet. The 6ES7421-1BL01-0AA0 supports shielded cable lengths up to 1000 meters (1 km) and unshielded lengths up to 600 meters. This allows sensors to be placed far from the rack without needing remote I/O or signal repeaters. For long cable runs, shielded cable is recommended to reject electromagnetic interference from motors, drives, and power lines. The module also provides optical isolation between the input circuits and the S7-400 backplane bus, tested at 500V DC.

        The 6ES7421-1BL01-0AA0 Siemens Digital Input Module may still be available for purchase and support from Apter Power beyond End-Of-Life (EOL)by the manufacturer (OEM).
        Siemens 6ES7421-1BL01-0AA0 Digital Input Module Manuals,Datasheets,Drivers,Link Important Notice:Other accessories,manuals,cables,calibration data,software,etc.are not included with this equipment unless listed in the above stock item description.All prices are shown in USD.
        Siemens 6ES7421-1BL01-0AA0 Digital Input Module Specs

        General

        • Manufacturer Siemens
        • Model 6ES7421-1BL01-0AA0
        • Condition New Original ready stock
        • Product Family 6ES7421-1BL00-0AA0,6ES7421-7BL01-0AB0,6ES7421-1BH01-0AA0
        Important Notice:Other accessories,manuals,cables,calibration data,software,etc.are not included with this equipment unless listed in the above stock item description.All prices are shown in USD.
        • Process Industry: Used in chemical plants, oil refineries, and water treatment facilities to monitor a vast array of digital sensors (level switches, pressure switches).
        • Automotive Production: Managing complex assembly lines and robotics where hundreds of status signals must be processed simultaneously.
        • Infrastructure & Power: Integrated into power distribution and large building automation systems to monitor circuit breaker statuses and safety interlocks.
        • Large-scale Manufacturing: Supporting heavy machinery like pulp and paper mills or metal processing plants.
        • High Signal Density: Features 32 digital input channels (24V DC) in a single module width, maximizing the utilization of rack space and reducing the overall footprint of the control cabinet.
        • Galvanic Isolation: Provides electrical isolation between the field signals and the internal S7-400 bus, protecting the CPU from external surges and increasing system reliability.
        • Fast Response Times: Optimized for low input delay (typically around 1.2 to 4.8 ms), ensuring that the controller reacts quickly to changes in the field status.
        • Energy Management: Designed for low internal power consumption from the backplane bus, allowing more modules to be powered by a single power supply unit.
        • Sensor Aggregation: Collecting signals from 32 different limit switches on a long conveyor system to track the position of materials in real-time.
        • Safety Status Monitoring: Feeding the status of multiple emergency stop buttons or gate interlocks (in a non-failsafe capacity) into the PLC logic for operational sequencing.
        • Sequence of Events (SOE): Detecting state changes in high-speed industrial processes to help operators troubleshoot the exact order of events during a system trip.
        • Remote I/O (ET 200M): Often installed in an ET 200M station connected via PROFIBUS or PROFINET, allowing for high-density digital monitoring far from the central CPU.
        Description
        The 6ES7421-1BL01-0AA0 is an SM 421 digital input module for SIMATIC S7-400 systems. It provides 32 digital input channels, each rated for 24V DC. The module has a typical power loss of 6 W and draws only 20 mA from the 5V backplane bus. Inputs are optically isolated as a single group of 32 channels. 

        When using the 6ES7421-1BL01-0AA0, engineers can connect up to 32 field devices such as pushbuttons, limit switches, or proximity sensors. The input voltage range for signal "1" is 13-30V DC, and for signal "0" it is -30V to +5V DC. Typical input current for signal "1" is 7 mA. 

        The 6ES7421-1BL01-0AA0 provides optical isolation between the inputs and the backplane bus, tested at 500V DC. All 32 channels are isolated together as one group; there is no isolation between individual channels. 

        For legacy S7-400 system expansions, the 6ES7421-1BL01-0AA0 provides reliable 32‑point digital input capability. It is a standard module in the S7‑400 I/O family. The product has a last modified date indicated but remains a current spare part. 
        Alternative Names
        6ES7421-1BLO1-OAAO 6ES742I-IBL0I-0AA0 6ES74211BL010AA0 6ES7421-7BH01-0AB0 6ES7422-1BL00-0AA0 6ES7421-7DH00-0AB0 6ES7421-1EL00-0AA0 6ES7421-1FH20-0AA0
        Technical notes
        The 6ES7421-1BL01-0AA0 has a wide input voltage range for signal "1" (13-30V DC). This allows the module to operate correctly even if the 24V supply drops to 13V (e.g., due to long cable runs or undersized power supplies). The module also accepts up to 30V without damage.
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        FAQS

        The following is a list of questions commonly asked by our customers. Please contact us if you have a question about our process that is not answered below.
        VIEW ALL FAQS
        Can I adjust the input delay on 6ES7421-1BL01-0AA0?
        Yes. The input delay (0→1) is configurable between 1.2 ms and 4.8 ms. The default setting is 4.8 ms. For faster response, set the delay to 1.2 ms using STEP 7. Shorter delay increases noise susceptibility; longer delay provides better filtering.
        How far can I place sensors from 6ES7421-1BL01-0AA0?
        Shielded cable length can be up to 1000 meters; unshielded up to 600 meters. This allows remote I/O placement without intermediate repeaters. For long runs, use shielded cable to reduce noise pickup and ensure signal integrity.
        How much current does 6ES7421-1BL01-0AA0 draw from the backplane?
        The module draws only 20 mA maximum from the 5V backplane bus. This is very low for a 32‑channel module, allowing more modules to be installed in the rack without exceeding the power supply capacity. Power loss is 6 W typical.
        What is the practical difference between the older 6ES7421-1BL00-0AA0 version and this 6ES7421-1BL01-0AA0 module?
        The older generation 6ES7421-1BL00-0AA0 conformed strictly to the obsolete IEC 61131 Type 2 electrical loading curve. The updated Siemens 6ES7421-1BL01-0AA0 model utilizes IEC 61131-2 Type 1 electrical input characteristics. This update optimizes current consumption profiles to match modern solid-state proximity sensors.
        Can the Siemens 6ES7421-1BL01-0AA0 be used in third-party distributed I/O systems over Profibus or Profinet?
        Yes, the Siemens 6ES7421-1BL01-0AA0 can be populated inside an ET 200M or compatible S7-400 distributed rack structure. When deployed in these sub-racks, its 32-bit process image is compiled into standard GSD/GSDML station configuration profiles. This allows any third-party Master controller to read its inputs using standard industrial network protocols.

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