The Allen-Bradley 1746-NR4 is a four-channel RTD and direct-resistance input module for the SLC 500 1746 I/O platform. Each channel is configured independently for its sensor type, excitation current, data format, and digital filter. The module reports converted values through the SLC image table and provides channel diagnostics for open-circuit, short-circuit, configuration, and out-of-range conditions.
Technical Specifications
| Catalog number |
1746-NR4 |
| Module type |
RTD/resistance input module |
| Input channels |
4, individually configurable |
| Supported RTDs |
Platinum 385 and 3916 (100, 200, 500, and 1000 ohm); Copper 426 (10 ohm); Nickel 618 and 672 (120 ohm); Nickel-Iron 518 (604 ohm) |
| Direct-resistance ranges |
0–150, 0–500, 0–1000, and 0–3000 ohm ranges; the 3000-ohm range is limited to 1900 ohm when 2.0 mA excitation is selected |
| Excitation current |
0.5 mA or 2.0 mA, selected per channel; the 10-ohm copper RTD requires 2.0 mA |
| Filter selections |
10, 50, 60, or 250 Hz |
| Step response |
300 ms at 10 Hz; 60 ms at 50 Hz; 50 ms at 60 Hz; 12 ms at 250 Hz |
| Backplane current |
50 mA at 5 V DC and 50 mA at 24 V DC |
| Input-to-backplane isolation |
500 V AC for 1 minute |
| Channel-to-channel isolation |
None |
| Common-mode separation |
±1 V maximum |
Wiring and Configuration
The 1746-NR4 accepts two-wire and three-wire RTDs. A four-wire sensor is connected as a three-wire device; one compensation lead is not used. For two-wire or three-wire circuits, use cable with consistent conductor impedance. Record the existing terminal assignment, sensor coefficient, excitation current, filter, temperature units, and data format before replacing a module.
The filter setting is an engineering trade-off. A 10 Hz filter gives stronger 50/60 Hz rejection but a 300 ms step response. The 250 Hz setting responds in 12 ms with less noise rejection. Changing this setting can alter both update time and measurement stability without any wiring change.
Installation and Replacement Notes
- Install the module in any modular SLC 500 chassis slot except slot 0.
- Check the chassis power budget for both the 5 V and 24 V backplane rails.
- Verify compatibility before using the module in a 1746-A2 fixed I/O expansion chassis.
- Do not substitute 1746-NR8 settings or terminal assumptions for the 1746-NR4.
- Confirm the channel status word before replacing hardware; recoverable sensor and configuration faults differ from non-recoverable module faults.
Documentation