Allen-Bradley 1756-IT6I ControlLogix Isolated Thermocouple/mV Input Module
The Allen-Bradley 1756-IT6I is a high-performance, isolated analog input module engineered exclusively for the Rockwell Automation ControlLogix platform. Above all, this module is purpose-built for precision temperature measurement, as it accepts six individually isolated thermocouple or millivolt (mV) inputs. Consequently, it serves as an ideal solution for critical process monitoring in demanding industrial environments. Furthermore, whether deployed in a local or remote I/O rack, the 1756-IT6I integrates seamlessly with any ControlLogix processor and communication module. As a result, it delivers consistently reliable and accurate data for temperature-critical applications across a wide range of automation setups.
Technical Specifications
The Allen-Bradley 1756-IT6I offers exceptional signal fidelity and remarkable flexibility in configuration. To begin with, its core technical parameters are outlined below to provide a comprehensive understanding of its capabilities:
Number of Inputs: 6 isolated thermocouple/mV channels + 1 Cold Junction Compensation (CJC)
Input Resolution: 16-bit
Supported Thermocouple Types: B, E, J, K, R, S, T, N, C, D, L (TXK/XK)
Input Ranges: -12 to 78 mV (standard) / -12 to 30 mV (high-resolution)
Accuracy: ±0.3 °C to ±3.2 °C (local CJC, channel-dependent); additionally, ±0.3 °C for a remote CJC
Module Scan Time:
For floating-point (mV): 25 ms minimum
For floating-point (temperature): 50 ms minimum
For integer (mV): 10 ms minimum
Data Formats: Integer mode (left justified, 2’s complement) and, alternatively, IEEE 32-bit floating point
Noise Rejection: Specifically, normal mode 60 dB @ 60 Hz; in comparison, common mode 120 dB @ 60 Hz / 100 dB @ 50 Hz
Input Impedance: 10 MΩ
Channel Bandwidth: 15 Hz (-3 dB)
Open Circuit Detection: Positive full-scale reading within 2 seconds
Overvoltage Protection: 120V AC/DC maximum
Backplane Current Draw: 250 mA @ 5.1V DC; likewise, 125 mA @ 24V DC
Power Dissipation: 4.3 W (maximum)
Thermal Dissipation: 14.66 BTU/hour
Temperature Drift (Gain): 65 ppm/°C (nominal); however, the maximum is 80 ppm/°C
Advanced Functionality
Beyond its basic input capabilities, the Allen-Bradley 1756-IT6I is equipped with a comprehensive suite of diagnostic and processing features. For instance, these include multiple input range selection, notch filtering, real-time sampling, and under-range/over-range detection. Moreover, the module also supports digital filtering, process alarms, rate alarms, 10-ohm offset compensation, wire-off detection, and flexible temperature unit selection (°C/°F). In addition, the module utilizes thermocouple linearization per ITS-90 standards, which ensures that your temperature readings remain as accurate as possible over time. Meanwhile, the Sigma-Delta conversion method contributes to excellent noise immunity and measurement stability. Therefore, this module not only captures signals but also processes them intelligently to enhance overall system reliability.
Installation & Mounting Guide
Installing the 1756-IT6I is straightforward for any technician familiar with the ControlLogix system. Nevertheless, to achieve optimal performance, please adhere to the following guidelines:
Chassis Compatibility: First, the module can be installed in any standard ControlLogix chassis slot. For safety, ensure the system power supply is turned off before insertion.
Slot Selection: Second, the 1756-IT6I is slot-independent; however, proper grounding and shielding practices should still be observed for thermocouple wiring.
RTB Requirement: Third, this module requires either the 1756-TBNH (screw clamp) or 1756-TBSH (spring clamp) Removable Terminal Block for signal connections. After wiring, ensure the RTB is firmly seated and locked.
Wiring Best Practices: Fourth, use shielded thermocouple extension wire to minimize electrical noise. Additionally, connect the shields to the designated ground terminal on the RTB, and route signal wires away from high-power AC cables.
CJC Sensor: Finally, note that the CJC sensor is located on the RTB; therefore, the terminal block must be properly installed for accurate cold junction compensation.
What’s in the Box
1 x Allen-Bradley 1756-IT6I ControlLogix Isolated Thermocouple/mV Input Module
1 x Product configuration label (pre-attached)
1 x Installation Instructions sheet (publication 1756-IN018)
*(For your reference, the Removable Terminal Blocks 1756-TBNH and 1756-TBSH are sold separately.)*
3-5 Frequently Asked Questions (FAQs)
Q1: What thermocouple types are compatible with the Allen-Bradley 1756-IT6I?
A: The 1756-IT6I supports a wide range of types, including B, E, J, K, R, S, T, N, C, D, and L (TXK/XK). In other words, it covers virtually all common thermocouple standards used in industrial temperature measurement.
Q2: Can the 1756-IT6I be used in a remote I/O rack?
A: Yes, absolutely. The 1756-IT6I is fully compatible with both local and remote ControlLogix I/O racks, provided that the appropriate communication modules are used in the system.
Q3: What is the difference between the standard and high-resolution input ranges?
A: Specifically, the standard range is -12…78 mV with 1.4 µV/bit resolution, whereas the high-resolution range is -12…30 mV with 0.7 µV/bit resolution. Thus, the latter provides finer granularity for lower-amplitude signals.
Q4: What type of terminal block does the 1756-IT6I require?
A: This module requires either the 1756-TBNH (screw-type) or the 1756-TBSH (spring-clamp) Removable Terminal Block. Notably, both are sold separately to allow flexibility based on your wiring preferences.
Q5: How does the module handle an open thermocouple circuit?
A: The 1756-IT6I features built-in wire-off detection. As a matter of fact, it guarantees a positive full-scale reading within 2 seconds of an open circuit being detected, enabling fast fault diagnosis and system protection.x
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