The Allen-Bradley 1797-IRT8, also cataloged as the 1797-IRT8 Thermocouple I/O Module, operates as a dedicated hardware component for high-resolution temperature sensor data acquisition within FLEX I/O networks. The module converts low-level analog signals from thermocouples and resistance temperature detectors (RTDs) into linearized temperature values for processing across the control architecture.

Functional Architectural Coding

• 1797: Bulletin identifier for intrinsically safe distributed I/O hardware (FLEX Ex).

• IRT: Designator for combined resistance temperature detector and thermocouple input instrumentation circuits.

• 8: Physical density value denoting eight independent analog hardware input channels.

Hardware Specifications

Deterministic Subsystem Configuration & Backplane Alignment

The processing architecture mounts onto compatible terminal base units, interfacing with field instrumentation via internal bus configurable pathways. Through network adapters, data frames flow over Profinet / EtherNet/IP deterministic networks without consuming unauthorized backplane bus communication velocity licenses. The internal logic maintains rigid firmware flash compatibility parameters during dynamic I/O density scaling events, protecting digital register updates from latency fluctuations.

Logistics Package Contents

• 1 Allen-Bradley 1797-IRT8 Thermocouple/RTD Input Module

• 1 Factory Calibration Certificate Sheet

Field Connection and Grounding Guidelines

• Mechanical Interlock Setting

  Rotate the terminal base keyswitch to position 2 prior to alignment. Press the module firmly onto the base until the side latches engage completely.

• Instrument Shielding Protocols

  Terminate all instrument cable braided shields at a single external grounding bar. Run thermocouple conductors inside dedicated conduits to avoid electromagnetic noise interference.

• Compensation Wire Rules

  Use matching thermocouple extension wire types for all sensor links. Ensure total lead resistance remains under 15 ohms to preserve calibration parameters.

Frequently Asked Questions

• What are the specific hardware restrictions regarding hot-swapping the module on an active base?

  Hot-swapping is permitted in non-hazardous locations, but the base parameters must remain stable to prevent bus communication disruptions.

• How does the internal logic handle a broken wire or disconnected sensor terminal path?

  The module triggers an open RTD detection sequence, forcing the data register to an out-of-range upscale reading value.

• Can channel 0 process an RTD loop while channel 1 simultaneously acquires a thermocouple input?

  Yes, the internal bus configurable architecture allows individual channel profiles to be parameterized independently for voltage or resistance modes.

• What is the settling time required for the input filter to reach 99% of a final step-change value?

  The analog-to-digital converter circuitry finishes stabilization and updates the data register within a target period of 8 ms.

• Does this module draw its operational current from the terminal base backplane bus?

  The module limits its field-side power consumption to 1.6 W, derived directly through the base connections from the barrier power source.

• What physical function does the keyswitch position 2 perform on the terminal base unit?

  It acts as a mechanical alignment guard, preventing the installation of high-voltage modules into low-voltage analog base configurations.

• How are communication velocity licenses adjusted when adding modules to the cluster?

  The module utilizes standard configuration files and requires no separate backplane bus communication velocity licenses to interface with adapters.

• Does the hardware track internal cold junction compensation drift autonomously?

  The internal circuit architecture samples local references to offset thermocouple junctions, adjusting calculations against environmental thermal variances.