ALLEN BRADLEY 1791D-4B4P Plc Modules

( Brand: Allen Bradley ), ( Manufacturer Part Number: 1791D-4B4P ), ( Part Type: Module )

Review ALLEN BRADLEY 1791d4b4p Used

The **Allen-Bradley 1791D-4B4P** is a high-performance, compact industrial controller module designed for integration into the **CompactLogix** series of programmable logic controllers (PLCs), specifically the **1769-L32ER** and **1769-L36ER** base units. This **4-channel, 4-bit binary input module** is engineered to provide reliable digital signal processing in demanding automation environments, offering a robust solution for applications requiring discrete input monitoring. Each of the four isolated input channels is rated for **24 30 VDC** or **115 264 VAC**, accommodating a wide range of standard industrial sensors, switches, and pushbuttons, while its **4-bit binary output** allows for efficient data transmission to the PLC s scan cycle. The module features **optically isolated inputs**, ensuring immunity to electrical noise and voltage spikes, which is critical in harsh factory settings where interference from motors, welders, or other high-power equipment can compromise system integrity. Its **compact, DIN-rail-mountable design** maximizes space efficiency in control panels, and the **LED status indicators** provide quick visual feedback on input states and module health, simplifying troubleshooting. Built to meet **IEC 61131-2** and **UL 508A** standards, the 1791D-4B4P is constructed with durable materials to withstand temperature extremes ranging from **-20 C to 60 C**, making it suitable for both indoor and outdoor industrial applications. Whether used in manufacturing, process control, or material handling systems, this module delivers consistent performance, seamless compatibility with Rockwell Automation s ecosystem, and the reliability expected from a leader in industrial automation technology.

The **Allen-Bradley 1791D-4B4P** is a compact digital I/O module designed for use in PLC systems, specifically compatible with Rockwell Automation controllers like the **ControlLogix** or **CompactLogix** platforms. Below is a detailed breakdown of its pros and cons, followed by a conclusion and recommendation.

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### **Pros of the 1791D-4B4P**

1. **High Reliability and Durability**

The 1791-D series is built to industrial standards, offering robust construction for harsh environments. It is designed to withstand temperature fluctuations, vibration, and electrical noise, making it suitable for manufacturing, process control, and automation applications.

2. **Compact and Space-Efficient Design**

As a **4-input, 4-output** module, it provides a balanced combination of I/O points in a single slot, reducing rack space requirements compared to larger modules. This is particularly useful in systems with limited I/O expansion slots.

3. **Digital Inputs and Outputs**

The module features **four isolated digital inputs** and **four isolated digital outputs**, which are ideal for controlling relays, sensors, actuators, and other binary devices. The isolation ensures protection against voltage spikes and ground loops.

4. **Compatibility with Rockwell Automation Ecosystem**

It integrates seamlessly with **ControlLogix, CompactLogix, and Studio 5000** platforms, leveraging Rockwell s programming environment (RSLogix, Studio 5000) for easy configuration, monitoring, and troubleshooting. This reduces development time and ensures long-term support.

5. **Easy Installation and Wiring**

The module follows a standardized design with clear labeling, screw-terminal connections, and a modular form factor. Wiring is straightforward, and the terminal block design allows for quick connections and disconnections.

6. **Low Power Consumption**

Compared to some other I/O modules, the 1791D-4B4P operates efficiently with minimal power draw, reducing heat generation and improving overall system energy efficiency.

7. **Diagnostic Capabilities**

Rockwell s programming software provides real-time monitoring of I/O status, fault detection, and diagnostic messages. This helps in quickly identifying issues such as short circuits, open circuits, or wiring problems.

8. **Long-Term Availability**

As part of Rockwell Automation s legacy product line, the 1791-D series has been in production for decades, ensuring continued availability of spare parts and support, even for older systems.

9. **Scalability**

The module can be easily integrated into larger systems with additional I/O modules, allowing for scalability as application requirements grow.

10. **Cost-Effective for Basic Applications**

For applications requiring a straightforward digital I/O solution without the need for advanced features (e.g., analog signals, high-speed counting), this module offers a cost-effective alternative to more complex or proprietary solutions.

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### **Cons of the 1791D-4B4P**

1. **Limited to Digital Signals Only**

The module does not support analog inputs or outputs, which may require additional modules (e.g., 1791-AEB for analog) if the application involves temperature, pressure, or other analog signals.

2. **No Built-in Communication Ports**

Unlike some newer I/O modules, the 1791D-4B4P does not include built-in Ethernet or wireless communication. Communication relies on the host PLC s network interface, which may require additional cabling or infrastructure.

3. **Outdated Technology Compared to Modern Alternatives**

- **Ethernet/IP integration** for faster data transfer.

- **Enhanced diagnostics** (e.g., device-level ring support).

- **Modular flexibility** with mixed I/O types in a single module.

- **Higher current ratings** for some outputs.

This may limit the module s suitability for cutting-edge automation systems.

4. **Potential for Obsolescence**

Rockwell Automation has phased out some older product lines in favor of newer, more integrated solutions. While the 1791D-4B4P is still supported, future updates or replacements may not be as seamless as with newer modules.

5. **Limited Output Current**

The digital outputs are rated for **0.5 A per point** (with a maximum of 2 A total for all outputs). For high-power applications (e.g., driving motors or heavy loads), external relays or higher-current modules may be required.

6. **No Built-in Isolation Monitoring**

Some newer I/O modules include **isolation monitoring** to detect faults in the isolation barrier. The 1791D-4B4P does not provide this feature, which could lead to undetected wiring issues until a failure occurs.

7. **Dependence on Rockwell Software**

Configuration and programming are tied to Rockwell s software suite (RSLogix, Studio 5000). Users relying on third-party PLCs or open-source alternatives may face compatibility challenges.

8. **Physical Size Constraints**

While compact, the module s size may still occupy a full slot in a **1756 or 1756-A8** chassis, which could be a limitation in space-constrained systems.

9. **No Built-in Redundancy or Fail-Safe Features**

The module does not support redundancy or fail-safe configurations out of the box. Applications requiring high availability may need additional hardware or software solutions.

10. **Potential for Higher Long-Term Costs**

While the upfront cost may be reasonable, the reliance on legacy parts and potential need for additional modules (e.g., for analog signals) could increase total system costs over time.

---

### **Conclusion**

The **Allen-Bradley 1791D-4B4P** is a **reliable, cost-effective, and easy-to-integrate** digital I/O module ideal for applications requiring **four isolated digital inputs and outputs** within a Rockwell Automation ecosystem. Its **durability, simplicity, and compatibility** with ControlLogix/CompactLogix platforms make it a strong choice for **basic automation tasks, legacy systems, or applications where analog signals are not required**.

However, its **lack of analog support, outdated communication features, and limited scalability** compared to newer modules may make it less suitable for **modern, high-speed, or complex automation systems**. Additionally, the **potential for obsolescence** and **dependence on Rockwell s software** could pose challenges for long-term maintenance or system upgrades.

For **new projects or applications requiring advanced features** (e.g., Ethernet/IP, analog I/O, higher current outputs, or redundancy), newer modules like the **1756-I/O series** or **CompactLogix with integrated I/O** may be more appropriate. Conversely, the **1791D-4B4P remains a solid choice for retrofitting, maintenance, or simple control applications** where cost and reliability are prioritized over cutting-edge features.

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### **Recommendation**

- You are working within a **Rockwell Automation ecosystem** (ControlLogix/CompactLogix) and need a **simple, reliable digital I/O solution**.

- Your application **does not require analog signals** or advanced communication features.

- You are **retrofitting an existing system** or maintaining a legacy setup where this module is already in use.

- Cost and ease of integration are **more important than the latest technology**.

- The module fits within your **budget and space constraints**.

- Your project requires **analog I/O, high-speed counting, or advanced diagnostics**.

- You need **Ethernet/IP or wireless communication** for modern automation.

- The application involves **high-power outputs** (beyond 0.5 A per point).

- You are building a **new system** and want to leverage the latest Rockwell Automation modules (e.g., **1756-I/O, 1756-A8, or CompactLogix with integrated I/O**).

- Long-term **scalability or redundancy** is a priority.

For **new installations**, evaluating newer modules (e.g., **1756-I/O modules**) may offer better performance, flexibility, and future-proofing. However, for **existing systems or cost-sensitive applications**, the **1791D-4B4P remains a practical and dependable option**. Always verify compatibility with your specific PLC and software version before purchasing.

Details:

Packaging and Handling: Items are safely ESD packaged in custom shipping cartons for protection. Call to use a shipping service other than the ones listed. Sells new and surplus product develops channels to purchase such. ALLEN BRADLEY 1791D-4B4P / 1791D4B4P USED DISCONTINUED BY MANUFACTURER, INPUT MODULE, 24 VDC SOURCE, DEVICENET, VDC, COMPACTBLOCK I/O, 4 IN SINK OUT COMBINATION BASE BLOCK.

All products are guaranteed to be working but may show signs of use if purchasing a used product.

part #: 1791d4b4p prices

• $40.49-$299.99

specifications sensoindustria:

• brand: Allen Bradley
• mpn: 1791d-4b4p
• part type: Module

seller sensoindustria:

• rating: 99.5%
• city: 1 Millennium Dr, Willingboro, NJ 08046
• # reviews: 190165

offer sensoindustria:

• started: February 14, 2026
• quantity: 1
• availability: In Stock
• options: Ship-to-home
• sold: 0

shipping sensoindustria:

• type: Fixed
• cost: $12.90
• transit: 25-38 Days
• class: Standard
• service: Standard

payments sensoindustria:

• credit card: Diners-club
• wallet: Paypal
• other

general sensoindustria:

• PLCs HMIs > PLC Peripheral Modules > PLC Input Output Modules
• condition: Used

returns sensoindustria:

• paid by: Buyer
• policy: Returns Accepted
• time: 30 Days
• method: Money back

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