Siemens SM 321 (6ES7 321-1BL00-0AA0) – SIMATIC S7-300 Digital Input Module (32 DI)

Siemens SM 321 (6ES7 321-1BL00-0AA0) – SIMATIC S7-300 Digital Input Module

The Siemens SM 321 (Part No. 6ES7 321-1BL00-0AA0) is a standard Digital Input Module for the modular SIMATIC S7-300 and ET 200M PLC systems. This module is essential for converting 32 separate 24 V DC field signals from devices like switches and proximity sensors into processable data for the CPU. Its robust, optically-isolated design ensures reliable and safe connection of field devices in various industrial applications.

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Quick Navigation

• About This Digital Input Module
• Applications
• Why ROMA Industrial Company
• Technical Specifications
• Key Features & Benefits

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About This Digital Input Module

This product is a Digital Input Module, often referred to as a **PLC Input Card** or **SM 321**, which serves as the interface between the physical world of sensors and the digital world of the PLC. The module connects up to 32 field devices operating on a 24 V DC signal. Key features include **optical isolation** between the inputs and the PLC backplane, which protects the sensitive electronics of the PLC from electrical noise or voltage spikes from the field. It is compatible with a wide array of sensors, including 2-, 3-, and 4-wire proximity sensors (BEROs), making it a versatile component for industrial automation.

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Applications

This digital input module is suitable for reading the ON/OFF status of devices in various industrial control systems, including:

• Machine Tool Position Sensing (using BERO/Proximity Sensors)
• Safety Interlocks and Limit Switches
• Control Panel Pushbuttons and Selector Switches
• General Binary Signal Monitoring in Manufacturing

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Why ROMA Industrial Company

ROMA Industrial is your trusted partner for a full range of industrial supplies across categories like Motion Control & Mechatronics, Electrical & Automation, and Fluid Power & Control. We are committed to providing top-tier products and service to keep your operations running smoothly. We partner with world-class shipping providers like FedEx, DHL, and UPS to ensure fast and reliable delivery worldwide. We accept returns to fulfill your satisfaction and accept variable payments methods including PayPal, credit cards, and more. We are a supplier in Europe, USA, and Saudi Arabia.

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Technical Specifications

• Manufacturer: Siemens
• Part Number: 6ES7 321-1BL00-0AA0
• Model Number: SM 321
• Product Type: Digital Input Module
• Number of Channels: 32 Digital Inputs
• Input Voltage: 24 V DC
• Input Delay: 1.2 ms to 4.8 ms
• Isolation: Optically Isolated (in groups of 16)
• Series: SIMATIC S7-300 / ET 200M
• Hazardous Location: Class I, Div 2 and Zone 2 Approved
• Front Connector: Requires 40-pole front connector (separate)

Key Features & Benefits

• High Channel Density: Provides 32 digital inputs in a single module, optimizing PLC rack space.
• Robust Isolation: Optically isolated inputs protect the PLC’s backplane from field disturbances.
• Wide Compatibility: Suitable for connecting standard switches and all common 2-/3-/4-wire proximity sensors.
• Reliable Performance: Fixed input delay ensures predictable signal reading times for consistent process control.