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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Number of Inputs | 6 individually isolated thermocouple + 2 CJC |
| Input Ranges | –12…78 mV; –12…30 mV (high-resolution) |
| Resolution | 16 bits (1.4 µV/bit or 0.7 µV/bit) |
| Supported Thermocouples | B, E, J, K, R, S, T, N, C, D, L (TXK/XK) |
| Thermocouple Linearization | ITS-90 |
| Backplane Current @ 5.1 V DC | 200 mA |
| Backplane Current @ 24 V DC | 150 mA |
| Total Backplane Power / Dissipation | 4.6 W |
| Thermal Dissipation | 15.7 BTU/hr |
| Open Circuit Detection | Positive full scale within 2 s |
| Overvoltage Protection | 120 V AC/DC |
| Input Impedance | > 10 MΩ |
| Removable Terminal Block | 1756-TBNH or 1756-TBSH |
| Operating Temperature | 0 °C to +60 °C |
4. Product Introduction
The Allen-Bradley 1756-IT6I2 is an enhanced 6-channel individually isolated thermocouple and millivolt input module for ControlLogix systems. It provides higher accuracy and dual cold-junction compensation (CJC) sensors compared with the earlier 1756-IT6I.
Each channel is isolated and can be configured for millivolt measurement or linearized temperature from thermocouple types B, E, J, K, R, S, T, N, C, D, or L. Two input ranges are available: the standard –12…78 mV range and a high-resolution –12…30 mV range. The module is commonly used for precision temperature monitoring in process, furnace, and machinery applications.
1756-IT6I2
1756-IT6I2
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| Channel reads full scale / open | Broken thermocouple or open wiring | ✅ High | Check open-circuit detection status | Repair or replace thermocouple / wiring |
| Incorrect temperature reading | Wrong T/C type selected or CJC fault | ✅ High | Verify sensor type configuration and CJC sensors | Select correct T/C type; reseat or replace CJC |
| High noise or unstable readings | Ground loops or poor shielding | ✅ High | Confirm isolation and cable shielding | Use proper thermocouple extension wire; improve grounding |
| Module OK LED off / faulted | Backplane power or configuration error | ❌ Medium | Verify chassis power and module properties | Reseat module; correct configuration in Studio 5000 |
| Slow update or high filter delay | Real-time sample or notch filter setting | ✅ Medium | Check RTS and filter settings | Increase sample rate or adjust notch filter |
| Channel-to-channel interference | Shared common or wiring error | ❌ Low | Verify each channel uses its own isolated return | Correct field wiring to maintain isolation |
If diagnostics remain unclear, capture channel status tags, configured sensor type, and measured millivolt values before contacting support.
6. Frequently Asked Questions (FAQ)
Q: Is the 1756-IT6I2 still in production? Yes. It remains an active enhanced thermocouple input module in the ControlLogix family.
Q: What is the difference between 1756-IT6I and 1756-IT6I2? The IT6I2 is the enhanced version. It adds support for thermocouple types D and L, dual cold-junction sensors for improved accuracy, and better overall performance compared with the original IT6I.
Q: How many cold-junction sensors does the module use? Two CJC sensors are provided with the module. Both should be installed for best accuracy.
Q: What terminal blocks are required? Use a 20-pin Removable Terminal Block: 1756-TBNH (screw-clamp) or 1756-TBSH (spring-clamp).
Q: Can each channel be set to a different thermocouple type? Yes. Sensor type and range are configurable on a per-channel basis.
Q: Does the module support grounded thermocouples? Yes. The channel-to-channel isolation allows both grounded and ungrounded thermocouples to be used.
Q: Why is New Surplus sometimes priced lower? These are genuine Allen-Bradley modules from excess inventory or cancelled projects. They are unused and typically supplied with anti-static protection. They are not refurbished unless specifically stated.
