Purchase now: Allen Bradley 1746-NR8 High-Density RTD Module
Purchase now: Atlantechdrives provides you the 1746-NR8, a high-density RTD (Resistance Temperature Detector) input module engineered by Allen Bradley for the robust SLC 500 platform. When panel space is at a premium but temperature monitoring needs are extensive, the 1746-NR8 is the ultimate solution. By offering 8 independent input channels in a single chassis slot, it doubles the capacity of the standard NR4. This module is heavily relied upon in large-scale HVAC systems, extensive boiler controls, multi-zone plastic extrusion lines, and power generation facilities where tracking dozens of temperature points simultaneously is crucial for machine safety and process quality.
Technical Specifications of the 1746-NR8
The 1746-NR8 utilizes advanced multiplexing technology to read 8 channels while maintaining rapid update times and exceptional accuracy. It translates the physical resistance of the metallic probes into high-resolution temperature data (Celsius or Fahrenheit) directly accessible by the PLC.
- Part Number: 1746-NR8
- Module Type: High-Density Analog RTD Input
- Compatible System: Allen Bradley SLC 500
- Number of Channels: 8 RTD or direct resistance inputs
- Supported RTD Types: Platinum (100, 200, 500, 1000 Ohm), Nickel, Copper
- Direct Resistance Range: 0 to 3200 Ohms
- Resolution: 16-bit
- Wiring Configurations: 2-wire or 3-wire RTDs
- Backplane Current Draw: 100 mA at 5V DC, 55 mA at 24V DC
Expert Tips: Shielding and Noise Mitigation
With 8 channels packed into one module, managing electrical noise is your highest priority. Expert Tip: RTD signals are low-voltage, highly sensitive analog signals. You must route your RTD cables in completely separate conduits from AC power lines or VFD motor cables. Use high-quality, shielded twisted-pair cables for every single sensor. The most critical step is grounding the shield: you must connect the cable shield drain wire to the ground bus bar at the PLC cabinet end ONLY. If you ground the shield at the sensor end on the machine frame, you will create a «ground loop» that will inject severe EMI into the 1746-NR8, causing the temperatures on your SCADA screen to fluctuate wildly.
Maintenance and Step Response Considerations
During commissioning and maintenance, remember that the 1746-NR8 is a multiplexed module. This means its internal A/D converter scans one channel, then moves to the next, until all 8 are read. If you configure the module for maximum digital filtering to smooth out a noisy signal, the channel update time will increase significantly (sometimes up to several seconds per scan cycle). For slow-changing processes like large water tanks, this is fine. For rapidly heating air ducts, you may need to reduce the filter settings in RSLogix 500 to catch temperature spikes before they trigger an alarm.
Frequently Asked Questions (FAQs)
Q: Does the 1746-NR8 support 4-wire RTDs?
A: While the 1746-NR4 supports 4-wire configurations, the high-density 1746-NR8 is physically limited by terminal space and primarily supports 2-wire and 3-wire RTD configurations. If you have a 4-wire RTD, you typically leave the fourth wire disconnected and wire it as a 3-wire system.
Q: Can I use this to measure standard potentiometer resistance?
A: Yes. You can configure the channels to read «Direct Resistance» (up to 3200 ohms) rather than a specific RTD temperature curve, making it excellent for reading linear potentiometers for position feedback.
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For high-density thermal monitoring, consider installing this 8-channel RTD unit in a 1746-A7 industrial chassis.
