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Phone: +86 16626708626Description
Key Technical Specifications
| Parameter | Value |
|---|---|
| Catalog Number | 1794-IT8 (also listed as 1794-IT8/A) |
| Module Type | Thermocouple / Millivolt Input Module |
| Number of Inputs | 8 individually isolated channels |
| Input Types | Thermocouple: B, C, E, J, K, N, R, S, T, L; mV: ±76.5 mV |
| Input Range | −76.5 to +76.5 mV (thermocouple and mV modes) |
| Resolution | 16 bits (2.384 µV typical) |
| Data Format | 16-bit 2’s complement or offset binary (unipolar) |
| Flexbus Current | 20 mA typical; 40 mA max @ 5 V DC |
| Input Voltage | 19.2–31.2 V DC (nominal 24 V DC) |
| Input Current | 150 mA max @ 24 V DC |
| Power Dissipation | 3 W max @ 31.2 V DC |
| Isolation Voltage | 850 V DC (inputs and user power to logic side) |
| Normal Mode Noise Rejection | −60 dB at 60 Hz |
| Channel Bandwidth | 0–2.62 Hz (−3 dB) |
| System Throughput | 325 ms per 8 channels (normal mode) |
| Cold Junction Compensation | 2 × factory-supplied CJC units (A-B 969424-0) |
| Terminal Base Units | 1794-TB2, -TB3, -TB3S, -TB3T, -TB3TS, -TB3G, -TB3GS, -TB3GK |
| Indicators | 1 × red/green power/status LED; 8 × red open-input LEDs |
| Mounting | DIN rail or panel mount (via terminal base) |
| Enclosure Rating | IP20 (open-style) |
| Operating Temperature | 0 to 55 °C (32 to 131 °F) |
| Storage Temperature | −40 to 85 °C (−40 to 185 °F) |
| Humidity | 5–95% non-condensing |
| Dimensions (H × W × D) | ~45.7 × 94 × 53.3 mm (1.8 × 3.7 × 2.1 in) |
| Weight | ~110 g (3.9 oz) |
| Certifications | UL, CE, CSA; ATEX/IECEx (European Zone 2) |
Product Introduction
The Allen-Bradley 1794-IT8 is an 8-channel thermocouple and millivolt input module for 1794 FLEX I/O systems. It accepts inputs from type B, C, E, J, K, N, R, S, T, and L thermocouples, as well as ±76.5 mV signals, with 16-bit resolution and individual channel isolation.
This module is chosen for temperature monitoring and process control applications where multiple thermocouple types must be read with high accuracy. In field deployments, it’s commonly used in ovens, furnaces, heat-treat systems, and process vessels where temperature profiling is critical.
1794-IT8
1794-IT8
1794-IT8
Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No power LED on module | 24 V DC supply missing or wiring fault | ✅ High | Measure 19.2–31.2 V DC at terminal base; check polarity and fuse | Fix 24 V DC supply and wiring before swapping module |
| All channels reading open or erratic | CJC unit missing or faulty | ✅ High | Verify cold junction compensator (CJC) is installed on terminal base | Install or replace CJC unit (A-B 969424-0) |
| One channel reading open | Thermocouple wire break or loose connection | ❌ Medium | Measure thermocouple resistance; check terminal screw torque | Repair or replace thermocouple; re-torque terminals |
| Inaccurate temperature readings | Wrong TC type configured or CJC error | ✅ Medium | Verify TC type in PLC config; measure CJC temperature | Correct TC type in software; verify CJC placement and function |
| Intermittent readings | Noise or grounding issue | ❌ Medium | Check shield grounding; verify separation from VFDs/motors | Improve shielding; ensure single-point ground |
| Power LED flashing red | Over-temperature or internal fault | ✅ High | Measure module temperature; check for hot spots | Improve airflow; replace module if fault persists |
If you’re stuck, send photos of the module (including LEDs), terminal wiring, and a screenshot of your PLC configuration. We’ll review it before you swap the module.
Frequently Asked Questions (FAQ)
Q: Is the 1794-IT8 hot-swappable?
A: No. The 1794-IT8 must be installed and removed with 24 V DC power OFF. Hot-swapping can damage the backplane and connected I/O modules.
Q: What’s the difference between 1794-IT8 and 1794-IR8?
A: IT8 is for thermocouple and mV inputs. IR8 is for RTD (resistance temperature detector) inputs. Do not substitute; they use different excitation and measurement circuits.
Q: Do I need a cold junction compensator (CJC) for the 1794-IT8?
A: Yes. The 1794-IT8 requires a CJC unit (A-B 969424-0) mounted on the terminal base for accurate thermocouple readings. Two CJC units are supplied with the module.
Q: What terminal bases work with the 1794-IT8?
A: Compatible terminal bases include 1794-TB2, -TB3, -TB3S, -TB3T, -TB3TS, -TB3G, -TB3GS, and -TB3GK. Ensure the base supports thermocouple wiring and CJC mounting.
Q: What condition are these modules in, and why is pricing lower than factory?
A: We sell New Original (New Surplus) and Refurbished (tested) units. Pricing is lower because these are surplus or professionally refurbished. Each refurbished unit goes through live functional testing and comes with a 1-year warranty.
Q: Can I keep my existing program when swapping a failed 1794-IT8?
A: Yes. As long as the replacement is the same catalog number (1794-IT8) and your PLC configuration (TC type, scaling, CJC settings) matches, the existing program should work without changes.
Q: What software do I need to configure the 1794-IT8?
A: RSLogix 5000 or Studio 5000 is used to configure the 1794-IT8 in a Flex I/O system. Set the thermocouple type, scaling, and CJC settings in the module configuration.
