Allen-Bradley 1791-NDC Analog Block I/O Module – 4 Inputs, 2 Outputs

Product Introduction

When your control system demands precise analog signal handling without the complexity of separate modules, the Allen-Bradley 1791-NDC Analog Block I/O Module delivers a compact, cost-effective solution. This module integrates 4 analog inputs and 2 current outputs into a single unit, reducing wiring, panel space, and installation labor. Operating on a 24V DC power supply at 600 mA, it is designed for seamless integration with Allen-Bradley PLC-2, PLC-3, PLC-5/250, PLC-5, and SLC 5/02 controllers. By combining multiple I/O points in one block, the 1791-NDC lowers total system cost while maintaining high accuracy and reliability.

Technical Specifications Breakdown

The 1791-NDC offers 4 analog inputs with selectable ranges: ±10V, ±5V, 0–10V, 0–50V, 0–20 mA, and ±20 mA, all with 14-bit resolution. This flexibility allows you to use a single module for various sensor types—voltage or current—reducing inventory and spare part costs. The update rate per channel is 108 ms, which is sufficient for most process monitoring and slow-speed control loops, avoiding the premium price of high-speed modules. Input bandwidth is 5 Hz, ideal for filtering out high-frequency noise in industrial environments. The 2 current outputs provide 0–20 mA with 13-bit resolution, ensuring fine control over actuators like valves and drives. Absolute accuracy is 0.1% at 25°C, minimizing calibration frequency and waste. Overvoltage protection up to 140V AC safeguards the module from accidental faults, preventing costly replacements. Power dissipation is 11.52 W max (thermal dissipation 39.28 BTU/hr), keeping energy costs low and reducing cooling requirements in the panel.

Industry Applications

In a chemical processing plant, the 1791-NDC monitors four pressure transmitters (0–20 mA) and controls two proportional valves. The 5 Hz input bandwidth filters out pump vibration noise, while the 0.1% accuracy ensures consistent product quality—reducing off-spec batches and material waste. For a packaging line, the module reads four analog sensors (e.g., tension or position ±10V) and adjusts servo drives via the 0–20 mA outputs. The 108 ms update rate is adequate for web tension control, avoiding the expense of faster, more costly modules. By consolidating I/O in one block, the 1791-NDC cuts installation costs by up to 30% compared to discrete modules, as fewer field wires and terminations are needed.

Installation & Setup Guidance

Mount the 1791-NDC on a DIN rail or panel using the provided slots. Connect 24V DC power (19.2–30V DC range) to the dedicated terminals, observing polarity. For analog inputs, use shielded twisted-pair cables to minimize noise—especially important given the 5 Hz bandwidth. Configure input type via software block transfer; no jumpers are needed. The module communicates via block transfer or discrete transfer with the host controller. Ensure the total current draw does not exceed 600 mA from the power supply. For loop-powered transducers, use the built-in 24V DC current-limited source. Verify that output loads are within 0–20 mA range and that short-circuit protection is active (indefinite). This straightforward setup reduces commissioning time and labor costs.

Maintenance & Reliability

The 1791-NDC is built for long service life with minimal maintenance. Its indefinite short-circuit protection on outputs prevents damage from accidental overloads, reducing downtime and repair costs. The module dissipates only 11.52 W of heat, so it operates coolly in enclosed panels, extending component life. Periodic inspection of connections and power supply voltage (19.2–30V DC) ensures consistent performance. The 0.1% accuracy drift of 75 ppm/°C is low, meaning calibration intervals can be extended—saving on maintenance labor and external service fees. For maximum reliability, keep ambient temperature within 0–60°C (if applicable, though not specified, it is typical for this class). By choosing the 1791-NDC, you invest in a module that minimizes total cost of ownership through robust design and low energy consumption.

Compatibility & Integration

The 1791-NDC integrates directly with Allen-Bradley PLC-2, PLC-3, PLC-5/250, PLC-5, and SLC 5/02 controllers via block transfer or discrete transfer. This broad compatibility allows you to standardize on one module across multiple machine generations, simplifying spare parts management and reducing training costs. No special communication adapters are needed—just standard 1771 or 1746 backplane connections. For new installations, the module works with modern control systems that support block transfer, ensuring a future-proof investment. Check your controller's user manual for block transfer programming details. This integration flexibility means you can upgrade older systems without replacing the entire I/O infrastructure, saving capital expenditure.

Selection Guide & Purchasing Advice

Before ordering the 1791-NDC, verify that your controller supports block transfer or discrete transfer communication. Confirm that your power supply can deliver 24V DC at 600 mA (minimum) and that your analog sensors match one of the supported input ranges (±10V, ±5V, 0–10V, 0–50V, 0–20 mA, ±20 mA). The module is compact (6.95 x 2.7 x 3.85 inches) and weighs only 1.00 lb (0.45 kg), so it fits easily into existing panels. For applications requiring more than 2 current outputs, consider pairing with additional 1791-NDC modules or a different model. BluePLC Industrial offers the 1791-NDC with fast shipping and expert support—contact us to check stock and lead times. We also provide compatible cables and accessories to complete your installation. Choose the 1791-NDC to reduce I/O cost per point while maintaining high analog accuracy.