Allen-Bradley 1791-24B8 Block I/O Module: Compact DC I/O Solution

Core Technical Specifications

• Brand & Manufacturer: Allen-Bradley
• Model Number: 1791-24B8
• Product Line: 1791 Block I/O
• I/O Configuration: 24 DC Inputs & 8 DC Sinking Outputs
• Input/Output Voltage Range: 10 to 30 Volts DC
• Nominal Voltage: 24 Volts DC
• External Power Supply: 19.2 to 30 Volts DC, 300 mA
• Module Dimensions: 6.95" x 2.7" x 3.85" (176.5 x 68.8 x 98 mm)
• Shipping Weight: Approx. 2.25 lbs (1.02 kg)

Detailed Input & Output Performance

• Input Groups: 24 inputs arranged in 3 groups of 8.
• Input Current: 11 mA maximum at 30V DC.
• Input Response Time: Selectable Fast (1ms ON/5ms OFF) or Slow (1ms ON/18ms OFF).
• Output Current Rating: Up to 0.5A per point (1.0A at reduced ambient temperature).
• Mounting Impact: Output current de-rates with horizontal mounting orientation.
• Surge Current: Outputs can handle 3A surge for 50ms, recurring every 2 seconds.

Environmental & Power Ratings

• Operating Temperature: 0°C to 60°C (32°F to 140°F).
• Relative Humidity: 5% to 95%, non-condensing.
• Power Dissipation: Maximum 17.1 Watts.
• Thermal Dissipation: Maximum 58.1 BTU/hour.
• Internal Protection: The external power supply includes internal protection circuitry.

FAQ - Frequently Asked Questions

• What is the main advantage of the 1791-24B8? Its compact design provides 32 DC I/O points with a wide 10-30VDC operating range for flexibility.
• Why does mounting orientation affect the output current? Thermal dissipation differs; vertical mounting allows better heat dissipation for higher continuous current.
• Can I use this module with 12V DC sensors? Yes, the input range of 10-30V DC fully supports common 12V and 24V DC sensors.
• What does "sinking output" mean? The output acts as a switch to ground (0V). The load connects between the output point and the positive DC supply voltage.

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