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Allen-Bradley 1746-NR8 Analog Input Modules
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- Part Number: 1746-NR8
- Brand: Allen-Bradley
- Type: Analog Input Modules
- Barcode: USA
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Product Description
The Allen-Bradley 1746-NR8, also cataloged as the 1746-NR8 RTD/Resistance Analog Input Module, operates as a dedicated hardware component for temperature and direct resistance signal acquisition within SLC 500 chassis assemblies.
Hardware Specifications
| Parameter | Specification |
|---|---|
| Brand | Allen-Bradley |
| Model | 1746-NR8 |
| Origin | USA |
| Weight | 0.31 kg (0.69 lbs) |
| Dimensions | Single-slot SLC 500 chassis footprint |
| Operating Temp | 0 to 60 deg C (32 to 140 deg F) |
| Power Consumption | 1.82 W maximum (0.5 W at 5 VDC, 1.32 W at 24 VDC) |
| Number of Inputs | 8 channels |
| Supported RTD Sensors | Platinum 100/200/500/1000 (385 & 3816), Copper 10 (426), Nickel 120 (618 & 672), Nickel-Iron 604 (518) |
| Resistance Input Ranges | 0 to 150 Ohms, 0 to 300 Ohms, 0 to 500 Ohms, 0 to 1000 Ohms |
| A/D Conversion | Sigma-delta modulation |
| Temperature Resolution | 0.01 deg C |
| Step Response | 60 ms in, 2.5 ms out |
| Channel Update Time | 6 ms to 2 s (dependent on channel configuration) |
| Backplane Current | 100 mA at 5 VDC, 55 mA at 24 VDC |
| Storage Temperature | -40 to 85 deg C (-40 to 185 deg F) |
| Module Location | Any chassis slot except Slot 0 |
Deterministic Backplane & I/O Density Scaling
The 1746-NR8 digitizes RTD and direct resistance field signals using high-resolution sigma-delta modulation, transmitting analog values directly to the host CPU data table over the SLC backplane bus. The module leverages internal firmware flash compatibility to support configurable channel updating, dynamic sensor linearization, and diagnostic filtering down to 0.01 deg C resolution. Backplane bus communication velocity allows simultaneous 8-channel acquisition across multiple local chassis expansion racks without degrading deterministic scan execution.
Frequently Asked Questions
Q: Can the 1746-NR8 module be installed in Slot 0 of an SLC 500 chassis?
A: No, Slot 0 is strictly reserved for the SLC 500 system CPU processor module. The 1746-NR8 may be installed in any other available expansion slot within the local chassis.
Q: How does wiring selection impact measurement accuracy when using 2-wire RTDs on the 1746-NR8?
A: 2-wire RTD configurations include line lead resistance in the measurement circuit, which degrades accuracy over long cable runs. Using lower gauge wire (e.g., AWG 16 instead of AWG 24) or switching to 3-wire/4-wire RTD sensors mitigates line resistance errors.
Q: What power sources are required to operate the 1746-NR8 RTD input module?
A: The module requires no external power supply; all internal operating power is drawn directly from the SLC chassis backplane power supply (100 mA at 5 VDC and 55 mA at 24 VDC).
Field Installation Guidelines
Verify that all system power sources supplying the SLC 500 chassis are turned off before inserting or removing the 1746-NR8 module from the backplane. Ensure the chassis slot keying corresponds to the analog module module type to avoid backplane pin damage.
Connect 2-wire RTD field devices using Belden 9501 shielded cable or equivalent. For 3-wire and 4-wire RTDs, utilize Belden 9533 or Belden 83503 shielded cable. Terminate cable shielding drain wires strictly at a single enclosure earth ground point to prevent ground loops. Observe that each screw terminal on the Removable Terminal Block (RTB) accepts only a single wire termination to maintain mechanical clamping force and low-impedance electrical contact.
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