Allen-Bradley 1756-IT6I ControlLogix Thermocouple Input Module

The Allen-Bradley 1756-IT6I, also cataloged as the 1756-IT6I Thermocouple/Isolated Input Module, operates as a dedicated hardware component for high-accuracy temperature sensing within ControlLogix backplane platforms. The module digitizes low-millivolt temperature signals across 6 channels, interfacing directly with field-mounted thermocouples or millivolt sensors. Each input channel features individual galvanic channel-to-channel isolation, preventing common-mode voltage interference and thermal noise propagation between ungrounded or grounded thermal junction probes.

Hardware Specifications

ControlLogix System Architecture & Backplane Protocol Features

The module communicates over the local ControlLogix backplane bus utilizing high-velocity CIP (Common Industrial Protocol) framing. Backplane bus communication velocity guarantees low deterministic latency during real-time thermal data processing. High-density I/O routing protocols ensure continuous cyclic data transmission to the controller, matching configured Requested Packet Interval (RPI) values down to sub-millisecond execution cycles. Firmware flash compatibility enables online parameter configuration and diagnostic updates via Studio 5000 Logix Designer software without interrupting backplane communication.

Frequently Asked Questions

Q: Can the 1756-IT6I module be removed or inserted under power (RIUP)?

A: Yes, the module supports Removal and Insertion Under Power (RIUP) within a ControlLogix chassis. However, cold junction compensation (CJC) thermistor connections located on the Removable Terminal Block (RTB) must remain firmly attached during operation to prevent thermal reference measurement errors.

Q: Does the 1756-IT6I provide onboard cold junction compensation (CJC)?

A: Cold junction compensation is performed by utilizing CJC thermistors embedded directly within the 1756-TBSA or 1756-TBSH Removable Terminal Block assemblies, allowing accurate ambient temperature offset adjustments for connected thermocouple leads.

Field Installation Guidelines

• Ensure backplane chassis grounding complies with IEEE 1100 standards by connecting the chassis grounding stud directly to the main cabinet star ground with low-impedance copper wire.
• Use dedicated thermocouple extension wire matched precisely to the specific thermocouple type (e.g., Type J, K, T, E, R, S, B, N) to prevent cold junction interface errors.
• Route low-level thermocouple signal lines in separate wiring raceways isolated from high-voltage AC cables and variable frequency drive output power leads.
• Ground the shield wire of shielded thermocouple cabling at a single end only (typically at the cabinet panel) to avoid creating ground loops across isolated channels.