Thermocouple Input Expander Module | Allen-Bradley 1771-IYC

The1771-IYCis a conformal-coated thermocouple input expander module engineered for the Allen-Bradley PLC-5 system architecture.It expands the temperature sensing capabilities of an associated analog input module by interfacing up to 8 floating differential thermocouple sensors across standard industrial millivolt ranges (+/- 99. 99 mV). Operating without external power, the module draws 750 mA directly from the 1771 I/O chassis backplane and uses block transfer programming to pass formatted temperature data to the PLC processor.

Signal Processing and Temperature Conversion

The module supports Type B, E, J, K, R, S, and T thermocouples, converting millivolt signals into a natural binary data format at a resolution of 15 bits plus sign (1. 0 deg C / 1. 0 deg F per bit). It features a fast channel update rate of 25 ms across all 8 channels. To maintain measurement accuracy without manual tuning, the unit incorporates automatic calibration for channel offset and gain, alongside continuous open-circuit detection and user-selectable high/low temperature alarms.

Chassis Installation and Keying

Occupying a single slot in any standard 1771 I/O chassis, the module requires chassis keying bands positioned between pins 20–22 and pins 24–26 to ensure proper slot alignment. Field wiring connects via a removable 1771-WI (or 1771-WH) wiring arm, enabling module replacement without disturbing individual field sensor leads. The module undergoes self-diagnostics at power-up to report hardware status to the main processor.

Frequently Asked Questions

Q: How does the 1771-IYC handle channel calibration for individual thermocouple inputs? A: The module automatically calibrates both offset and gain for every channel, eliminating the need for manual potentiometer adjustments during commissioning or routine maintenance.

Q: What keying band positions are required for installing the 1771-IYC into a 1771 I/O chassis? A: Keying bands must be installed on the chassis backplane connector between pins 20 and 22,and between pins 24 and 26,to prevent accidental insertion of incorrect module types.