Siemens 6ES7221-1BF22-0XA8 SIMATIC S7-200 CN EM 221 8DI 24V DC Input Module

Overview

SIEMENS SIMATIC S7-200 CN

6ES7221-1BF22-0XA8 SIMATIC S7-200 CN EM 221 8DI 24V DC Input Module

An eight-input EM 221 expansion module for S7-200 CN systems, using 24 V DC sink/source inputs in a 46 mm-wide housing.

At a Glance

Brand	Siemens
Model	6ES7221-1BF22-0XA8
Product Type	EM 221 digital input expansion module
Core Function	Reading DC switch and sensor signals
Application	Supported S7-22X CPUs

DC sensor inputs

Eight sink/source inputs accept 24 V DC field signals.

CPU power budget

The expansion module needs 30 mA from the CPU’s 5 V supply.

Defined response

The expansion inputs have a maximum 4.5 ms input delay.

Product Overview

6ES7221-1BF22-0XA8 adds eight 24 V DC digital inputs to a supported S7-22X CPU in the SIMATIC S7-200 CN system.

Its sink/source wiring supports suitable field switches and proximity sensors, while optical isolation, signal thresholds and fixed expansion-input delay determine how the module should be connected and used.

Ordering focus: Retain the CN suffix 0XA8, check CPU expansion capacity and the 5 V power budget, and match the common wiring to the selected sensor polarity.

Key Functions

Wire sinking or sourcing field devices

The DC input circuit supports sink/source arrangements, with a minimum ON threshold of 15 V DC at 2.5 mA and a maximum OFF threshold of 5 V DC at 1 mA.

Extend ordinary digital acquisition

The module provides eight expansion inputs with a maximum delay of 4.5 ms, making signal duration an important selection criterion.

Plan the CPU and sensor supplies

Allow 30 mA from the 5 V expansion supply and approximately 4 mA per active input from the field circuit.

Official Specifications

Digital Input Points	8
Rated Input Signal	24 V DC at 4 mA
Input Circuit	Sink/source; IEC Type 1 sinking input
Maximum Continuous Input Voltage	30 V DC
Maximum Surge Input Voltage	35 V DC for 0.5 s
ON-State Threshold	At least 15 V DC at 2.5 mA
OFF-State Threshold	At most 5 V DC at 1 mA
Maximum Input Delay	4.5 ms
Maximum Two-Wire Sensor Leakage	1 mA
Field-to-Logic Isolation	Optical; 500 V AC test for 1 minute
Maximum Signal-Cable Length	500 m shielded; 300 m unshielded
Simultaneous Input Operation	All inputs at 55 °C horizontal or 45 °C vertical
5 V Expansion-Supply Requirement	30 mA
Typical Power Dissipation	2 W
Dimensions (Width × Height × Depth)	46 × 80 × 62 mm

Official source:Siemens S7-200 System Manual

Frequently Asked Questions

Which CPU generation is required for 6ES7221-1BF22-0XA8?

The EM 221 expansion module is intended for supported S7-22X CPUs.

Can I wire 6ES7221-1BF22-0XA8 for both sinking and sourcing sensor arrangements?

The 24 V DC input circuit supports sinking and sourcing arrangements when the input common is wired for the selected sensor polarity.

Will a very short pulse be reliably captured by 6ES7221-1BF22-0XA8?

The expansion inputs have a maximum 4.5 ms delay, so the application must provide input signals long enough for reliable recognition.

How much of the CPU’s 5 V power budget does 6ES7221-1BF22-0XA8 use?

The module requires 30 mA from the 5 V expansion supply.

What leakage limit applies to two-wire sensors on 6ES7221-1BF22-0XA8?

The maximum permissible leakage current for a two-wire proximity sensor is 1 mA.

How far can I run the sensor cable to 6ES7221-1BF22-0XA8?

The maximum input-cable length is 500 m when shielded or 300 m when unshielded.

Can every channel of 6ES7221-1BF22-0XA8 stay on at the upper installation temperature?

All inputs may be on simultaneously at 55 °C in a horizontal installation or 45 °C in a vertical installation.

Compatibility & Ordering Notes

Before ordering 6ES7221-1BF22-0XA8: Specify the complete S7-200 CN article, verify the S7-22X CPU expansion limit and available 5 V current, and choose sensor wiring that matches the module’s input common arrangement.

Compatibility Checklist for 6ES7221-1BF22-0XA8

• Use the EM 221 with a supported S7-22X CPU and include it in the CPU’s expansion-module and power-budget calculations.
• Retain 0XA8 when ordering the CN variant; the Siemens cross-reference links it to the EM 221 8 × 24 V DC wiring and performance specifications.
• Select sinking or sourcing wiring for the sensor and observe the input common arrangement.
• Keep the input continuously at or below 30 V DC and size the signal duration for the maximum 4.5 ms delay.
• Allow for reduced full-input temperature limits in vertical installations and provide the required enclosure ventilation.

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