Siemens 6ES7421-7BH01-0AB0

SM 421 digital input, 16 DI, 24 V DC, interrupt and diagnostics

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Maker: Siemens
Part no.: 6ES7421-7BH01-0AB0
Serial / rev.: as printed on your unit

Image is for illustrative purposes only. Please refer to product description.

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Siemens SIMATIC S7-400 SM 421 digital input module: 16 isolated inputs, 24 V DC, hardware interrupt, diagnostics and wire-break detection, two short-circuit-proof encoder supplies.

Manufacturer: Siemens
Manufacturer part no.: 6ES7421-7BH01-0AB0
Product family: SIMATIC S7-400 PLC CPUs, I/O and Function Modules
Type: Digital input module
Category: PLCs and I/O › Digital I/O modules
Lifecycle: Discontinued
OEM successor: Not stated
Technical datasheet: Data sheet

Technical specifications

Manufacturer: Siemens
Manufacturer part no.: 6ES7421-7BH01-0AB0
Type: Digital input module
Application: Digital input module
Used with: SIMATIC S7-400 rack
Load voltage L+ / Rated value (DC): 24 V
Load voltage L+ / permissible range, lower limit (DC): 20.4 V
Load voltage L+ / permissible range, upper limit (DC): 28.8 V
Load voltage L+ / Reverse polarity protection: Yes
Input current / from supply voltage L+, max.: 120 mA
Input current / from backplane bus 5 V DC, max.: 130 mA
Encoder supply / Number of outputs: 2
Encoder supply / Type of output voltage: L+ (-2.5 V)
Encoder supply / Short-circuit protection: Yes; Electronic
Encoder supply / additional (redundant) feed: Yes; possible
Output current / Rated value: 120 mA
Output current / permissible range, lower limit: 0 mA
Output current / permissible range, upper limit: 150 mA
Power loss, typ.: 5 W
Number of digital inputs: 16
Digital inputs / Input characteristic according to IEC 61131: Type 2
Number of simultaneously controllable inputs / Number of simultaneously controllable inputs: 16
Input voltage / Type of input voltage: DC
Input voltage / Rated value (DC): 24 V
Input voltage / for signal "0": -30 V DC to +5 V DC
Input voltage / for signal "1": 11 V DC to 30 V DC
Input current / for signal "0", min.: 6 mA; < 6 mA
Input current / for signal "1", typ.: 6 mA; 6 to 8 mA
Input delay (for rated value of input voltage) / Input frequency (with a time delay of 0.1 ms), max.: 2 kHz
Input delay (for rated value of input voltage) / for standard inputs / parameterizable: Yes

Show all 56 specifications

Input delay (for rated value of input voltage) / for standard inputs / at "0" to "1", min.: 3 µs; 0.05 / 0.1 / 0.5 / 3 ms
Encoder connection / Fixed current limitation for wire-break monitoring, min.: 10 kΩ
Encoder connection / Fixed current limitation for wire-break monitoring, max.: 18 kΩ
Cable length / shielded, max.: 1 000 m; 1 000 m: 3 ms, 70 m: 0.5 ms, 30 m: 0.1 ms, 30 m: 0.05 ms
Cable length / unshielded, max.: 600 m; 600 m: 3 ms; 50 m: 0,5 ms; 20 m: 0,1 ms; 20 m: 0,05 ms
Connectable encoders / 2-wire sensor: Yes
Connectable encoders / 2-wire sensor / permissible quiescent current (2-wire sensor), max.: 3 mA
Interrupts/diagnostics/status information / Diagnostics function: Yes; Parameterizable
Alarms / Diagnostic alarm: Yes; Parameterizable
Alarms / Hardware interrupt: Yes; Parameterizable
Diagnoses / Diagnostic information readable: Yes
Diagnoses / Monitoring the supply voltage: Yes
Diagnoses / Wire break: Yes; I < 1 mA
Diagnostics indication LED / Rated load voltage PWR (green): Yes; Per group
Diagnostics indication LED / internal fault INTF (red): Yes
Diagnostics indication LED / external fault EXTF (red): Yes
Diagnostics indication LED / Status indicator digital input (green): Yes
Diagnostics indication LED / Channel fault indicator F (red): No
Potential separation digital inputs / between the channels: Yes
Potential separation digital inputs / between the channels, in groups of: 8
Potential separation digital inputs / between the channels and backplane bus: Yes
Isolation tested with: 500 V DC
Width: 25 mm
Height: 290 mm
Depth: 210 mm
Weight, approx.: 600 g

Technical documents (1)

Siemens data sheet 6ES7421-7BH01-0AB0

Key features

16 digital inputs, 24 V DC, IEC 61131 type 2
Parameterizable hardware and diagnostic interrupts, wire-break detection
Input frequency up to 2 kHz with a 0.1 ms input delay
Two short-circuit-proof encoder supplies, 120 mA each
Discontinued by Siemens on 1 October 2026

About the Siemens 6ES7421-7BH01-0AB0

The Siemens 6ES7421-7BH01-0AB0 is the fast diagnostic SM 421: 16 inputs at 24 V DC with an input delay from 0.05 ms (Siemens's description), hardware and diagnostic interrupts and wire-break detection, where the 6ES7421-1BL01-0AA0 has 32 plain inputs. Siemens's data sheet gives IEC 61131 type 2 inputs, signal "1" at 11 to 30 V DC, two encoder supplies with electronic short-circuit protection and 5 W typical power loss. SiePortal shows its phase-out announced on 1 October 2025 and its product cancellation on 1 October 2026.

What is the 6ES7421-7BH01-0AB0 used for?

It reads fast-changing 24 V DC signals into an S7-400 CPU where the program has to react at once or know when a sensor cable is broken.

Lifecycle and successor

Discontinued.

Before you order

What to photograph or confirm so the right unit is quoted.

Check the order number on the module: 7BH01 is the 16-channel diagnostic version, 1BL01 the 32-channel standard one.

Other parts in the Siemens SIMATIC S7-400 family

Listed for reference. They differ from the 6ES7421-7BH01-0AB0 in rating, supply, interface or function and are not interchangeable with it unless Siemens says so. Match the part number on your unit.

Product	Type	Lifecycle	Qty Available	Price	Action
Siemens 6ES7417-4XT05-0AB0CPU 417-4, 30 MB, MPI, PROFIBUS DP and 2 IF slots	PLC CPU	Discontinued	On Request	On request	View
Siemens 6ES7414-4HM14-0AB0CPU 414-4H for S7-400H/F/FH, 2.8 MB, MPI/DP, DP and 2 sync interfaces	Redundant PLC CPU (H-CPU)	Discontinued	On Request	On request	View
Siemens 6ES7416-3FS07-0AB0CPU 416F-3 PN/DP fail-safe, 16 MB, MPI/DP, PROFINET and IF slot	Safety PLC CPU (F-CPU)	Phased out	On Request	On request	View
Siemens 6ES7421-1BL01-0AA0SM 421 digital input, 32 DI, 24 V DC	Digital input module	Discontinued	On Request	On request	View
Siemens 6ES7422-1BL00-0AA0SM 422 digital output, 32 DO, 24 V DC, 0.5 A	Digital output module	Discontinued	On Request	On request	View
Siemens 6ES7421-1EL00-0AA0SM 421 digital input, 32 DI, 120 V AC/DC	Digital input module	Discontinued	On Request	On request	View
Siemens 6ES7421-1FH20-0AA0SM 421 digital input, 16 DI, 120/230 V AC/DC	Digital input module	Discontinued	On Request	On request	View
Siemens 6ES7421-7DH00-0AB0SM 421 digital input, 16 DI, 24 to 60 V AC/DC, interrupt and diagnostics	Digital input module	Discontinued	On Request	On request	View
Siemens 6ES7422-1BH11-0AA0SM 422 digital output, 16 DO, 24 V DC, 2 A	Digital output module	Discontinued	On Request	On request	View
Siemens 6ES7422-7BL00-0AB0SM 422 digital output, 32 DO, 24 V DC, 0.5 A, diagnostics	Digital output module	Discontinued	On Request	On request	View
Siemens 6ES7422-1FH00-0AA0SM 422 digital output, 16 DO, 120/230 V AC, 2 A	Digital output module	Discontinued	On Request	On request	View
Siemens 6ES7422-1HH00-0AA0SM 422 relay output, 16 DO, 5 A	Digital output module	Discontinued	On Request	On request	View

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