Procure 1771-OBN now for high-density digital control
The Allen-Bradley 1771-OBN is a high-density, 32-point Digital DC Output Module designed for the legacy PLC-5 control platform. Operating as a high-true sourcing module, it delivers 10-30V DC power directly to a wide array of automated field devices, providing millions of cycles of reliable solid-state operation.
Technical Specifications
- Output Channels: 32 high-density sourcing outputs, arranged in 4 sets of 8.
- Operating Voltage: 10 to 30 Volts DC.
- Maximum Current Per Output: 0.5 Amps.
- Maximum Module Current: 8.0 Amps total.
- Backplane Current Draw: 330 mA at 5V DC.
Advanced Performance and Sourcing Architecture
The 1771-OBN condenses significant control capabilities into a single I/O chassis slot, effectively condensing two full 16-point module groups into one space. It operates using a sourcing configuration, which means it switches the positive voltage path out to the load, requiring a grounded sink input connection at the field device. This design is an industry standard for maximizing safety, as a short-to-ground on the field wire will not accidentally energize the machine actuator. This module is frequently deployed in demanding discrete manufacturing applications, driving relays, pneumatic solenoid valves, motor contactors, and panel indicator lights. Additionally, the front panel features 32 individual status indicators, providing maintenance personnel with immediate visual feedback on the logic state of every single output. If an output is commanded ON by the processor but the field device is inactive, the LED helps pinpoint whether the failure is within the PLC program or the external field wiring.
Critical Installation Advice
Because this is a high-density 32-point module, thermal dissipation and power budgeting are primary engineering concerns. Before installation, calculate your backplane power requirements; the 1771-OBN draws 330mA from the chassis logic supply. Exceeding the backplane limit will cause system faults. Furthermore, while the module is rated for 0.5 Amps per individual channel, the total continuous current for the entire module must never exceed 8 Amps. Ensure that external fast-acting fuses are installed in series with your field wiring to protect the module’s internal solid-state circuitry from short circuits.
Expert Maintenance Tips
High-density output cards generate heat, particularly when driving multiple inductive loads simultaneously. Ensure that your PLC-5 cabinet is well-ventilated and that cooling fans are operational to keep the ambient temperature below the maximum rated 60°C. For heavy inductive loads (such as large solenoids), we strongly advise installing external flyback diodes across the load to suppress back-EMF voltage spikes, which can prematurely degrade the module’s switching transistors.
Frequently Asked Questions (FAQs)
Q: Can I use the 1771-OBN in an older 1771-A1 or 1771-A2 chassis?
A: No, the 1771-OBN requires a modern chassis and is explicitly not compatible with 1771-A1, 1771-A2, or 1771-A4 racks.
Q: Does this module require an external power supply?
A: Yes, you must provide an external 10-30V DC power supply to the module’s terminals to drive the connected output devices. The backplane only powers the internal logic.
System Integration & Related Components
To complete your digital control setup, the 1771-OBN output module pairs seamlessly with the high-density 1771-IBD input module. You can also monitor the physical results of these digital commands by integrating a 1771-IFE analog card.
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