Purchase now: Allen Bradley 1746-NT4 Thermocouple Module
Purchase now: Atlantechdrives provides you the 1746-NT4, a highly advanced analog input module designed by Allen Bradley for the SLC 500 controller system, dedicated strictly to Thermocouple and low-millivolt (mV) measurements. While RTD modules (like the NR4) are great for lower temperatures, the 1746-NT4 is mandatory for extreme industrial environments. It is engineered to read the tiny voltage signals generated by the «Seebeck effect» in dissimilar metals, allowing it to monitor the extreme heat of smelting furnaces, industrial kilns, glass extruders, and gas turbine exhausts. With 4 isolated input channels, it offers unparalleled accuracy in environments where standard sensors would literally melt.
Technical Specifications of the 1746-NT4
The 1746-NT4 is a sophisticated piece of hardware featuring built-in Cold Junction Compensation (CJC) sensors on the terminal block, which is mathematically essential for accurate thermocouple readings. It supports a massive range of industry-standard thermocouple types, making it universally adaptable.
- Part Number: 1746-NT4
- Module Type: Thermocouple / Millivolt Analog Input
- Compatible System: SLC 500 (1746 Series)
- Number of Channels: 4 Differential inputs
- Supported Thermocouples: Types J, K, T, E, R, S, B, N
- Millivolt Ranges: +/- 50mV, +/- 100mV
- Resolution: 15-bit
- Cold Junction Compensation: Included (Built into the RTB)
- Backplane Current Draw: 60 mA at 5V DC, 40 mA at 24V DC
Expert Installation Advice: The Golden Rule of Thermocouple Wire
Thermocouple installation has strict metallurgical rules that cannot be ignored. Expert Tip: When wiring a thermocouple to the 1746-NT4, you must use the exact matching thermocouple extension wire all the way from the probe head to the module’s terminal block. For example, if you are using a Type K thermocouple, you must use Type K (Yellow/Red) extension wire. If you splice standard copper wire in the middle of the run, you will create two new «unintended» thermocouple junctions at the splice points. This will severely corrupt the millivolt signal, and the PLC will read a wildly inaccurate temperature. Never mix wire types, and never use standard copper terminal blocks in a thermocouple circuit.
Maintenance: Heat Placement and CJC Preservation
The accuracy of the 1746-NT4 relies heavily on its internal Cold Junction Compensation (CJC) thermistors located on the removable terminal block. These thermistors measure the ambient air temperature right at the connection point to calculate the true probe temperature. Maintenance Warning: Never install the 1746-NT4 in a chassis slot directly next to a module that generates a lot of heat (such as a 220V AC output module or a heavy relay card). The radiant heat will artificially warm the CJC sensors, throwing off the calibration of all 4 thermocouple channels. Always position the NT4 in the coolest part of your SLC 500 rack.
Frequently Asked Questions (FAQs)
Q: What happens if a thermocouple wire breaks during operation?
A: The 1746-NT4 features built-in «Open-Circuit Detection.» If a wire breaks or burns out, the module will force the channel’s data word to a specific extreme value (user-configurable to maximum or minimum) and set an error bit, allowing your PLC logic to instantly trigger a safe machine shutdown.
Q: Can I replace the terminal block with a standard one?
A: No. You must use the specific Allen Bradley RTB designed for the NT4, because it contains the physical CJC sensors embedded inside the plastic housing. A standard RTB will result in total calibration failure.
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Achieve precise thermocouple measurements by utilizing this module alongside a dedicated 1746-P1 system power supply.
