1790D-T4R0 Allen-Bradley RTD Module 4-Ch DeviceNet CompactBlock

1790D-T4R0 Allen-Bradley 4-Channel RTD Input Module for DeviceNet

Product Introduction

The 1790D-T4R0 from Allen-Bradley belongs to the CompactBlock LDX I/O family. This module provides four dedicated RTD or resistance input channels. It reads signals from Resistance Temperature Detectors (RTDs), converts them into digital temperature values, and sends the data over a DeviceNet network.

You can connect up to four independent RTD sensors to this module. The input resistance range is 1 ohm to 625 ohms. Resolution reaches 0.1 °C per bit for RTD sensors or 100 milliohms for resistance measurements. The 1790D-T4R0 uses a 20-bit Sigma-Delta converter and outputs 16-bit integer data.

Technical Specifications

• Number of inputs: 4 channels, RTD or resistance input

• Input range: 1…625 Ω

• Supported RTD types:

  • Pt100 / Pt200 / Pt500 (α = 0.00385 or α = 0.003916)

  • Nickel: 100Ω, 120Ω, 200Ω, 500Ω

• Resolution: 16 bits across 625Ω, 0.1 °C/bit or 0.1 °F/bit for RTD sensors

• Converter: 20-bit Sigma-Delta modulation

• Data format: 16-bit integer (2’s complement)

• Module scan time: 8 ms per channel (at 60 Hz notch filter)

• Overall accuracy: 0.2% full scale @ 0…55 °C

• Excitation current: 1 mA

• Input impedance: 5 MΩ

Settable Notch Filter

The 1790D-T4R0 includes a programmable notch filter to reduce line noise. Available frequencies are:

• 10 Hz (default)

• 25 Hz

• 50 Hz

• 60 Hz

• 100 Hz

• 250 Hz

• 500 Hz

Open Wire Detection

This module supports open wire detection. If an RTD sensor wire breaks or disconnects, the 1790D-T4R0 reports an "out of range" signal to the processor. This feature helps you quickly identify faulty sensors.

Power Requirements and Dissipation

The 1790D-T4R0 requires two separate power sources.

• DeviceNet power: 24V dc nominal (voltage range 11…28.8V dc). Maximum power dissipation is 1.2 W @ 28.8V dc.

• Field power: 24V dc nominal (voltage range 21.6…26.4V dc). Maximum power dissipation is 1.5 W @ 26.4V dc.

Isolation and Protection

• I/O to logic: Photocoupler isolation, type tested at 1250V ac rms for 60 seconds

• DeviceNet to logic: Nonisolated

• Field power: Nonisolated

Mechanical and Environmental Specifications

• Weight: 0.44 lbs (0.20 kg)

• Operating temperature: 0…55 °C

• Mounting options: DIN rail or screw mounting

• Indicators: 4 red/green I/O status LEDs

• Wiring terminal: M3.0 screw type, maximum torque 7 lb-in

• Conductor type: Copper or copper-clad aluminum only

• Expansion: This base module does not accept additional expansion modules

Installation Guidelines

Follow these steps to install the 1790D-T4R0 correctly.

1. Turn off DeviceNet network power before starting any wiring.

2. Connect field power (21.6…26.4V dc) to the designated terminals.

3. Wire each RTD sensor to its input channel. Use three-wire or four-wire connections for best accuracy.

4. Tighten all terminal screws to 7 lb-in maximum. Do not overtighten.

5. Select the appropriate notch filter frequency and RTD type via software.

6. Apply power and check the I/O status LEDs.

Furthermore, use shielded RTD extension cables to reduce electrical interference. Keep RTD wiring separate from power cables and motor drives. For more than four temperature points, install an additional 1790D-T4R0 base module.

Packaging List

• 1790D-T4R0 module (1 unit)

• Terminal block (factory installed)

• Quick start guide

Note: No certificates or warranty documents are included in the package.

Shipping

We ship worldwide via FedEx, UPS, or DHL. Orders are dispatched within 1-2 business days.

Frequently Asked Questions (FAQ)

1. Which RTD sensors work with the 1790D-T4R0?

The 1790D-T4R0 supports Pt100, Pt200, Pt500 (with α = 0.00385 or 0.003916) and Nickel RTDs (100Ω, 120Ω, 200Ω, 500Ω).

2. Can I add expansion modules to this RTD base?

No. The 1790D-T4R0 does not accept any expansion modules. For more than four inputs, install another base module.

3. What is the scan time for all four channels?

Each channel scans in 8 milliseconds at the 60 Hz notch filter setting. The total scan time for all four channels is 32 milliseconds.

4. Does the module detect broken RTD wires?

Yes. Open wire detection is supported. The processor receives an "out of range" signal when a wire breaks.

5. How do I mount the 1790D-T4R0?

You can mount it on a standard DIN rail or use screw mounting. Both options are supported.