The 1746-NT8 is an SLC 500 Thermocouple/mV Analog Input Module by Allen-Bradley. It is an Eight (8) channel chassis installed module which receives thermocouple/mV signal which is digitally converted for retrieval by any SLC 500 processors. It has a backplane rating of 120mA at 5V DC and one of 70mA at 24V DC with an overall backplane power of 2.28W. The 1746-NT8 uses a Delta-Sigma signal conversion method and it has a digital low pass filter with selectable programmable filter frequencies. Its normal mode rejection frequency between the terminals is greater than 100dB at 50-60 Hz and its common mode rejection frequency between inputs and ground is also above 100dB at 50-60 Hz. The 1746-NT8 module automatically calibrates itself from power approximately every 2 minutes after power up. It offers input overvoltage protection at +/-30V DC and 600W pulsed for 1ms and provides 12.5V DC circuit isolation tested at 500V DC for 1 minute between inputs and the chassis ground and between the inputs and backplane.

The 1746-NT8 has 9 green LED lights that indicate a channel status and the module’s status. It uses the 1746-RT34 (RTB) removable terminal block for connection input devices. Included with the terminal block are Two (2) cold-junction compensation (CJC) sensors with an accuracy of +/-1.72 deg. Celsius. The 1746-NT8 has various selectable input types and the with an overall input impedance is greater than 10 M Ohms. Any input devices connected to it must have an impedance of fewer than 100 Ohms to meet the accuracy level. The 1746-NT8 offers a selectable open-circuit detection with 1 cycle per channel and an overall input stem response time of 400ms. The module has a functional temperature range between 0 deg. Celsius and 60 deg. Celsius at 5-95% humidity without condensation and is UL and CUL-approved.

The 1746-NT8 is an analog input module that belongs to the SLC 500 product family. This module is specifically a Thermocouple / millivolt that is compatible with SLC 500 processors such as SLC 5/01, 5/02, 5/03, 5/04 and 5/05. It may be used with SLC fixed style or modular hardware category.

Similar to other analog input modules, the 1746-NT8 converts the receive analog signal to a digital value using Sigma-Delta modulation. The converted data is save to the module’s local memory which is communicated to the CPU for creating a data table where the digitally converted values are stored.

This module may be installed in a fixed style chassis specifically using a 1746-A2 chassis. If used with a modular style controller, this module may be installed in any slot except slot 0. Slot 0 is always reserved for the controller or communication adapters such as a Remote IO, Data Highway Plus (DH+) and Ethernet communication module.

The data formats available for the input signal include engineering units, Scaled for Proportional-Integral-Derivative (PID) and Proportional counts. Scaled for PID is the most compatible data format for Thermocouple and millivolt input signals.

This module is capable of detecting Open circuit, Under-Range, Over-Range and Channel Error. These error alarms are assigned with specific bits that may be accessed by monitoring systems such as Human Machine Interface (HMI) and Supervisory Control and Data Acquisition (SCADA) systems.