Allen-Bradley 1794-IRT8 Flex IO 8-Channel RTD / Thermocouple Input Module

Description

The 1794-IRT8 module is an Allen-Bradley FLEX I/O millivolt, thermocouple, and RTD module. In a FLEX I/O system, the 1794-IRT8 module is connected to a terminal base and a power adapter. The Allen-Bradley 1794-IRT8 is shipped with 2 cold junction compensators. This cold junction compensator increases the accuracy of the module for Thermocouple mode. 1794-IRT8 module has a nominal voltage rating of 24 Volts DC and 8 analog inputs. It can connect to up to 8 RTD or thermocouple inputs. The front panel of the 1794-IRT8 module has a nameplate that identifies the module, a removable label that the users can customize, a keyswitch position indicator, and LED status indicators.

General Specifications

Attribute	Value
Number of Inputs	8 channels (2 groups of 4)
Module Location	1794-TB36, 1794-TB3GS, 1794-TB3GK terminal base units
Nominal Input Voltage Ranges	-40…+100 mV DC (Thermocouples), 0…325 mV DC (RTDs)
Resolution	14 bits
Accuracy	0.05% of full range (millivolt mode with filtering), 0.10% (hardware only)
Common Mode Rejection	-80 dB @ 5V peak-to-peak, 50…60 Hz
Common Mode Input Range	Minimum: ±15V
Power Dissipation (max)	3.0W @ 31.2V DC
Thermal Dissipation (max)	10.2 BTU/hr @ 31.2V DC

Supported Thermocouple Types

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

Supported RTD Types

Type	Resistance	Temperature Range (°C)
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

Attribute	1794-IRT8	1794-IRT8XT
Operating Temperature	-20…+55 °C (-4…+131 °F)	-20…+70 °C (-4…+158 °F)
Non-operating Temperature	-40…+85 °C (-40…+185 °F)	Same
Surrounding Air Temperature (max)	55 °C (131 °F)	70 °C (158 °F)
Relative Humidity	5…95% noncondensing	Same
Vibration	5 g @ 10…500 Hz	Same
Shock (Operating)	30 g	Same
Shock (Non-operating)	50 g	Same

Electrical and Wiring

Attribute	Value
External DC Power Supply Voltage	24V DC nominal (19.2…31.2V DC, includes 5% AC ripple)
Supply Current	95 mA @ 24V DC
Signal Conductors	Shielded thermocouple wire (e.g., Belden 8761)
Wiring Category	2 (signal ports), 3 (power ports)

Additional Specifications

Attribute	Value
Isolation Voltage	50V (continuous), Type tested at 1365V AC for 60s
Cold Junction Compensation Range	-20 to +100 °C
Indicators	1 green (power), 8 red (open input)
Keyswitch Position	3

Series A vs. Series B Differences

Common Mode Range:
- Series A: +4V DC
- Series B: +15V DC
Thermocouple Wire-off Detection:
- Series A: Defaults to max value
- Series B: Defaults to min value