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) |
Temperature Range (°F) |
| 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
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