Allen Bradley 1746-NT4

Product Features

Allen Bradley 1746-NT4 features 4 independent channels, supporting J, K, T, E, R, S, B, and N type thermocouples, as well as ±50 mV and ±100 mV DC millivolt signals.

Allen Bradley 1746-NT4 is compatible with all SLC 500 fixed and modular controllers and supports remote configuration via Block Transfer.

Allen Bradley 1746-NT4 terminal block integrates 2 CJC sensors to compensate for temperature offset at the thermocouple connection point, ensuring measurement accuracy.

Allen Bradley 1746-NT4 supports open-circuit, over-range, and under-range detection, indicating faults via channel status LED flashing and status word bit indicators. The module status LED (green) displays the overall operational status of the module, the 4 channel status LEDs (green) display the operational or fault status of the corresponding channels (solid for normal, flashing for fault).

Each channel can be independently configured for input type (thermocouple/mV), data format (engineering units, PID scaling, ratio counting), filter frequency (10 Hz/50 Hz/60 Hz/250 Hz), temperature units (°C/°F), etc. No DIP switches are required, configuration is achieved by writing configuration bits to the output image table via user programs (RSLogix 500).

Allen Bradley 1746-NT4 is factory-calibrated and supports automatic calibration functionality to compensate for offset and gain drift caused by temperature changes in the A/D converter. Automatic calibration is triggered when a channel is enabled, the input type or filter frequency is changed, or it can be manually triggered via software (by disabling and then re-enabling the channel).

Product Working Principle

Allen Bradley 1746-NT4 thermocouple or mV signal is connected to the channel via a terminal block, and the multiplexer sequentially switches the signals from the four channels to the A/D converter.

The CJC sensor continuously measures the temperature of the terminal block to compensate for the cold-junction voltage offset of the thermocouple.

The A/D converter converts the analog signal into a digital value, which is then stored in the data word of the input mapping table after digital filtering.

Allen Bradley 1746-NT4 communicates with the SLC processor via the chassis backplane, receiving configuration information (configuration words of the output mapping table) and returning measurement data and status (data words and status words of the input mapping table).

The configuration words define parameters such as the input type, data format, and filtering frequency of the channel, the status words reflect the validity of the channel configuration and fault status (such as open circuit, out of range).

Allen Bradley 1746-NT4 can scan all enabled channels and update data at a specified time, calculated as “the sum of sampling times for all enabled channels + CJC update time (14 ms).” The time it takes for the input signal to transition from change to reach 100% of its final value depends on the filter frequency (such as a 10 Hz filter corresponds to 300 ms).

Product Parameter

The following detail is for Allen Bradley 1746-NT4 Thermocouple/mV Input Module.