Purchase now: Allen Bradley 1746-NT8 Thermocouple Module
Purchase now: Atlantechdrives provides you the 1746-NT8, a high-density, highly advanced analog input module engineered by Allen Bradley for the proven SLC 500 programmable logic controller family. Designed specifically for complex thermal processes, this module doubles the capacity of standard analog thermal cards, providing 8 independent input channels dedicated to reading thermocouple and low-millivolt (mV) signals. It is an indispensable hardware component for large-scale industrial applications such as multi-zone extrusion lines, commercial bakery ovens, metal smelting furnaces, and comprehensive environmental control chambers. By consolidating 8 high-precision temperature readings into a single chassis slot, the 1746-NT8 maximizes panel space efficiency while delivering critical, real-time thermal data to the PLC processor.
Technical Specifications of the 1746-NT8
The 1746-NT8 converts millivolt-level analog signals into highly accurate 16-bit digital integers. It comes equipped with integral Cold Junction Compensation (CJC) thermistors embedded in its specific Removable Terminal Block (RTB), ensuring that ambient temperature fluctuations in the control cabinet do not corrupt the process temperature readings.
- Part Number: 1746-NT8
- Module Type: High-Density Thermocouple/mV Analog Input
- Compatible System: SLC 500 (1746 Series)
- Number of Channels: 8 Differential inputs
- Supported Thermocouples: Types J, K, T, E, R, S, B, N
- Millivolt Ranges: +/- 50mV, +/- 100mV
- Resolution: 16-bit (Superior precision)
- Cold Junction Compensation: Dual CJC sensors on RTB
- Backplane Current Draw: 120 mA at 5V DC, 70 mA at 24V DC
Expert Tips: Multiplexing and Update Times
When dealing with high-density analog modules, you must understand how data is processed. Expert Tip: The 1746-NT8 uses a multiplexer to scan its 8 channels. This means it reads channel 0, then channel 1, and so on sequentially. If you configure the module via RSLogix 500 to use a heavy digital filter (low cut-off frequency) to eliminate electrical noise, the «step response time» (the time it takes for the PLC to see a sudden temperature change) will increase significantly. For a large vat of liquid that heats slowly, a 1-second update time is perfectly fine. However, if you are monitoring the exhaust gas of a rapid-fire turbine, you must lower the filter settings to ensure the module updates the processor fast enough to trigger safety shutdowns.
Maintenance and Wiring Integrity
Thermocouple signals are incredibly weak (often just a few millivolts). During maintenance, ensure that no electrical power cables are routed alongside the thermocouple extension wires. Furthermore, you must ensure that the specific RTB (Removable Terminal Block) used is the exact OEM model intended for the NT8, as standard copper RTBs lack the required CJC thermistors. If a wire breaks in the field, the module’s built-in open-circuit detection will flag the channel, allowing the PLC to fail-safe.
Frequently Asked Questions (FAQs)
Q: Can I use different types of thermocouples on the same module?
A: Yes. Each of the 8 channels is fully independent and can be individually configured in the software to read a different thermocouple type (e.g., Type J on Ch0 and Type K on Ch1) or a direct mV signal.
Q: Will this module work for RTDs?
A: No. Thermocouples and RTDs operate on entirely different physics (Seebeck effect vs. resistance). For RTD probes, you must use the 1746-NR4 or 1746-NR8 modules.
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This 8-channel thermocouple card is a standard fit for large process control racks like the 1746-A10 10-slot chassis.
