Allen-Bradley 1790D-T4R0 CompactBlock LDX 4-Channel RTD Input Module

Product Overview

When real-time temperature data is critical for your process, the Allen-Bradley 1790D-T4R0 CompactBlock LDX I/O 4-channel input RTD base module delivers reliable digital transmission over DeviceNet. This RTD input module collects resistance measurements from up to four sensors and converts them into 16-bit integer data for your control system. With support for a wide range of RTD types—including 100 Ohm, 200 Ohm, and 500 Ohm platinum sensors with various alpha coefficients—the 1790D-T4R0 provides the flexibility needed for diverse temperature monitoring applications.

Technical Specifications

The 1790D-T4R0 offers 4 channels of RTD/resistance input with an input range of 1 to 625 Ohms. It achieves a resolution of 16 bits across 625 Ohms, or 0.1 °C per bit for RTD sensors, using a 20-bit Sigma-Delta modulation converter. The module scan time is 8 milliseconds per channel at a 60 Hz notch filter setting. Overall accuracy is 0.2% of full scale at 0 to 55 °C. Settable notch filter frequencies include 10 Hz (default), 25 Hz, 50 Hz, 60 Hz, 100 Hz, 250 Hz, and 500 Hz. Open wire detection is supported and reported as an out-of-range signal. Excitation current is 1 mA, and input impedance is 5 mOhms.

For DeviceNet power, the supply voltage is 24 V DC nominal, with a voltage range of 11 to 28.8 V DC. Maximum power dissipation is 1.2 W at 28.8 V DC. Field power requires 24 V DC nominal, with a range of 21.6 to 26.4 V DC (+10%), and maximum power dissipation of 1.5 W at 26.4 V DC. Isolation between I/O and logic is provided by photocoupler isolation, with a type test isolation voltage of 1250 V AC RMS for 60 seconds. DeviceNet to logic and field power are nonisolated. The module includes four red/green I/O status indicators and uses a terminal block with M3.0 screws (maximum torque 7 lb-in, using copper or copper-clad aluminum conductors).

Industry Applications

The 1790D-T4R0 is ideal for temperature-critical processes such as plastic injection molding, food processing, and chemical batch reactors. In a plastic molding application, the module monitors mold temperature via RTD sensors, sending precise 0.1 °C resolution data to the PLC over DeviceNet. This enables tight temperature control that improves product quality and reduces scrap. For food processing, the module can track pasteurization or cooking temperatures, ensuring compliance with safety standards. Its compact size (weight 0.44 lbs) and low power dissipation make it easy to deploy in space-constrained control panels.

Installation and Mounting

The 1790D-T4R0 supports both DIN rail and screw mounting, giving you flexibility for different panel layouts. Use copper or copper-clad aluminum conductors for wiring, and tighten terminal screws to a maximum of 7 lb-in. No additional expansion modules are accepted, so plan for one base module per four RTD points. The module automatically detects open wiring and reports it as an out-of-range signal to the processor, simplifying troubleshooting during commissioning.

Compatibility and Integration

This module communicates via the DeviceNet network using digital data format of 16-bit integers. It works with any DeviceNet-compatible master scanner or PLC, including Allen-Bradley ControlLogix and CompactLogix controllers with a DeviceNet interface. The module does not require additional expansion modules; for more than four RTD inputs, simply add another 1790D-T4R0 base module.

Selection Guide and Purchasing Advice

Before purchasing the 1790D-T4R0, verify your DeviceNet network configuration and ensure you have the correct power supply (24 V DC nominal for both DeviceNet and field power). Confirm the RTD sensor types you plan to use—the module supports platinum and nickel RTDs with various alpha coefficients. For applications requiring more than four inputs, order multiple base modules. BluePLC Industrial stocks the Allen-Bradley 1790D-T4R0 and can assist with compatibility questions. Please verify current lifecycle status and availability before ordering.