Allen-Bradley 1756-IRT8I/A ControlLogix RTD/Thermocouple Input Module

The Allen-Bradley 1756-IRT8I/A, also cataloged as the 1756-IRT8I/A RTD/thermocouple analog input module, operates as a dedicated hardware component for temperature signal acquisition within ControlLogix backplane I/O systems. Configured for RTD and thermocouple conversion in ControlLogix networks, the Allen-Bradley 1756-IRT8I/A (1756-IRT8I/A temperature input module) provides direct electrical measurement of resistance and millivolt-level sensor outputs across 8 individually isolated channels.

Suffix Breakdown & Model Matrix

• 1756: ControlLogix chassis-based I/O platform

• IRT8: 8-channel RTD / thermocouple input structure

• I: Individually isolated input architecture

• /A: Hardware revision identifier

No additional variant segmentation is defined in the provided dataset.

Hardware Specifications

ControlLogix Backplane Deterministic Temperature Acquisition Behavior

The 1756-IRT8I/A executes sigma-delta conversion per channel prior to ControlLogix backplane data publication. Temperature values derived from RTD resistance or thermocouple millivolt input are normalized into engineering units within module firmware before cyclic transfer to controller memory.

Channel-to-channel isolation maintains electrical separation between mixed sensor types during simultaneous sampling. Cold junction compensation is executed internally using dual reference sensors, ensuring thermocouple EMF correction independent of terminal block temperature variation.

Backplane scan timing is governed by chassis slot configuration and controller task rate, with minimum module input scan capability down to 1 ms under optimized configuration.

Frequently Asked Questions (FAQ)

Q: Can RTD and thermocouple inputs be mixed on the same module?
A: Yes. Each of the 8 channels supports independent configuration for RTD or thermocouple input types, allowing mixed sensor deployment within a single module.

Q: How does channel isolation affect temperature measurement stability?
A: Channel-to-channel isolation prevents electrical interaction between sensor loops, reducing measurement drift caused by ground potential differences or shared return paths.

Q: What is the role of cold junction compensation in this module?
A: The module uses two internal CJC sensors to correct thermocouple junction voltage, compensating for terminal temperature variations at the RTB interface before digitization.

Field Installation Guidelines

• Install module into a compatible 1756 ControlLogix chassis slot with system power removed or per approved insertion procedure

• Ensure RTB or 1492 IFM connector is fully seated prior to energizing field wiring

• Use shielded twisted pair wiring for thermocouple inputs; terminate shield at one end only

• Maintain separation between low-level millivolt sensor wiring and high-voltage conductors to reduce induced noise

• Verify correct sensor type configuration (RTD or thermocouple) before loop energization

• Avoid exceeding specified input range (resistance or mV) during commissioning to prevent conversion errors