I/O modules

Description

The Allen-Bradley 1794-IRT8 module offers precise temperature and millivolt measurement across eight input channels. It supports both thermocouples and RTDs, operating with a nominal 24V DC supply. Two cold junction compensators are included for improved thermocouple accuracy. The module fits terminal bases such as 1794-TB36, 1794-TB3GS, and 1794-TB3GK, making it adaptable to diverse FLEX I/O systems.

General Specifications

• Inputs: 8 channels (2 groups of 4)
• Supported Bases: 1794-TB36, 1794-TB3GS, 1794-TB3GK
• Input Ranges: -40…+100 mV DC (Thermocouples), 0…325 mV DC (RTDs)
• Resolution: 14 bits
• Accuracy: 0.05% full scale with filtering
• Common Mode Rejection: -80 dB at 50–60 Hz
• Common Mode Range: ±15V minimum
• Power Dissipation: 3.0W at 31.2V DC
• Thermal Dissipation: 10.2 BTU/hr at 31.2V DC

Supported Thermocouple Types

• Type B: 300…1800 °C (572…3272 °F)
• Type E: -270…+1000 °C (-454…1832 °F)
• Type J: -210…+1200 °C (-346…2192 °F)
• Type K: -270…+1372 °C (-454…2502 °F)
• Type TXK/XL: -200…+1372 °C (-328…2502 °F)
• Type N: -270…+1300 °C (-454…2372 °F)
• Type R: -50…+1768 °C (-58…3214 °F)
• Type S: -50…+1768 °C (-58…3214 °F)
• Type T: -270…+400 °C (-454…752 °F)

Supported RTD Types

• 100 Ω Pt (α=0.00385 Euro): -200…+870 °C (-328…+1598 °F)
• 200 Ω Pt (α=0.00385 Euro): -200…+400 °C (-328…+752 °F)
• 1000 Ω Pt (α=0.003916 U.S.): -200…+630 °C (-328…+1166 °F)
• 100 Ω Pt (α=0.003916 U.S.): -200…+400 °C (-328…+752 °F)
• 100 Ω Nickel: -60…+250 °C (-76…+482 °F)

Environmental Specifications

• Operating Temperature: -20…+55 °C (1794-IRT8), -20…+70 °C (1794-IRT8XT)
• Storage Temperature: -40…+85 °C
• Surrounding Air: 55 °C (IRT8), 70 °C (IRT8XT)
• Humidity: 5…95% non-condensing
• Vibration: 5 g at 10…500 Hz
• Shock: 30 g operating, 50 g non-operating

Electrical and Wiring

• External Power: 24V DC nominal (19.2…31.2V DC)
• Supply Current: 95 mA at 24V DC
• Signal Wiring: Shielded thermocouple wire (Belden 8761 recommended)
• Wiring Category: 2 (signal), 3 (power)

Additional Specifications

• Isolation Voltage: 50V continuous, tested at 1365V AC for 60s
• Cold Junction Range: -20…+100 °C
• Indicators: 1 green (power), 8 red (open input)
• Keyswitch Positions: 3

Series A vs. Series B Differences

• Common Mode Range: +4V DC (Series A) vs. +15V DC (Series B)
• Thermocouple Wire-Off Detection: Max value default (Series A) vs. Min value default (Series B)

Details