1734-IT2I Thermocouple Input Replacement Guide

Overview

In industrial thermal management, precise temperature monitoring is critical for process stability, safety, and quality control. The Allen-Bradley 1734-IT2I is a highly specialized, 2-channel, individually isolated thermocouple input module belonging to the POINT I/O family. Engineered for high-density, remote I/O architectures, this module is commonly deployed in applications where ground potential differences otherwise disrupt sensor accuracy.

When replacing or servicing these modules within an active automation chassis, control engineers and electrical technicians must pay close attention to mechanical keying, cold junction compensation (CJC) wiring, and software configuration in RSLogix 5000 or Studio 5000 Logix Designer. This guide provides comprehensive, field-tested technical steps to successfully execute a 1734-IT2I module replacement with minimal downtime.

Legacy Product Information

The 1734-IT2I is an active-mature product within the Rockwell Automation lifecycle, meaning that while it is still manufactured, many legacy systems in the field utilize older series hardware.

Key Technical Specifications

• Channels: 2 isolated, single-ended inputs
• Thermocouple Types Supported: J, K, T, E, R, S, B, N
• Millivolt Range: -110 mV to +110 mV
• Resolution: 16 bits (15 bits plus sign); 3.4 µV/count
• Isolation: 50V continuous (channel-to-channel and channel-to-system), tested to 2500V DC for 1 second
• POINTBus Current Draw: 175 mA @ 5V DC
• Power Dissipation: 1.5 W maximum
• Keyswitch Position: Position 6 (required on the mounting base)

Common Applications

The isolated design of the 1734-IT2I makes it ideal for environments prone to electrical noise and ground loops. Typical installations include:

• Plastic extrusion lines and injection molding machines.
• Heat-treating furnaces, annealing lehrs, and industrial kilns.
• Chemical reactors and refinery temperature-monitoring arrays.
• Applications requiring thermocouple probes that are directly grounded to metallic vessels or piping.

Recommended Replacements

When a 1734-IT2I fails or is scheduled for a proactive system modernization, there are three primary paths forward. Below is a replacement selection matrix based on system requirements:

Compatibility Considerations

Before replacing a 1734-IT2I, several electrical, mechanical, and software dependencies must be evaluated to prevent application mismatches or hardware damage.

1. Terminal Base and CJC Requirements

The 1734-IT2I cannot achieve accurate temperature conversion without Cold Junction Compensation. It must be paired with the 1734-TBCJC terminal base assembly, which incorporates an integrated thermistor that monitors the ambient temperature at the module's terminal screw connections. If you attempt to plug a 1734-IT2I into a standard 1734-TB or 1734-TBS base, the module will suffer from severe temperature drift and reference errors.

2. Physical and Footprint Compatibility

The physical form factor of the POINT I/O module remains identical across all series letter revisions. However, the mechanical keyswitch on the terminal base must be set to Position 6 before inserting the 1734-IT2I. If replacing a different module type in that slot, verify that the keyswitch is correctly aligned; forcing a module onto incorrectly configured keyswitches will damage the backplane pins.

3. Software Configuration and AOP

In Studio 5000, the Add-On Profile (AOP) defines parameters like Notch Filter frequency (50 Hz, 60 Hz, 250 Hz, or 500 Hz), thermocouple sensor type, data format (Raw/Proportional, Engineering Units, Percent of Full Scale), and temperature scale (Celsius or Fahrenheit).

• Electronic Keying: If replacing a Series A module with a Series B, you may encounter an I/O configuration mismatch error. Set the Keying option in the module properties connection tab to "Compatible Module" or "Disable Keying" if you want to avoid altering the controller's hardware profile configuration online.

Upgrade Benefits

Replacing an older Series A 1734-IT2I with a current production Series B or Series C module offers significant operational enhancements:

• Enhanced Firmware Stability: Newer revisions feature refined internal cold-junction compensation algorithms, reducing measurement drift in high-vibration or rapidly fluctuating ambient thermal environments.
• Improved Noise Rejection: Modern components resist electromagnetic interference (EMI) and radio frequency interference (RFI) more effectively, preventing erratic temperature spikes in the PLC controller tags.
• Extended Life Support: Transitioning to current series hardware ensures supply-chain durability and compliance with modern industrial standards (CE, UL, ATEX Zone 2).

Common Migration Challenges

Technicians often face a few distinct hurdles during a 1734-IT2I migration:

• Massive Temperature Offsets (CJC Faults): After replacement, the controller may read temperature values that are off by tens of degrees. This occurs when the internal CJC thermistor is wired backwards or damaged, or when a standard terminal base (1734-TB) is used without external CJC integration.
• Ground Loop Noise on Replacements: If a non-isolated 1734-IT2 is substituted for an isolated 1734-IT2I to save costs, ground loops can form through the thermocouple sheaths. This leads to erratic readings, signal clipping, or damage to adjacent I/O modules on the POINT I/O backplane.
• Firmware Keying Faults: After hot-swapping or replacing a failed unit, the adapter profile LED flashes green, and the Logix controller registers a connection fault (Code 16#0114 Electronic Keying Mismatch). Adjusting the keying parameters in Studio 5000 is required to resolve this state.

Step-by-Step Replacement Procedure

Follow these precise steps to safely replace a 1734-IT2I module:

Phase 1: Preparation and Safety

1. Isolate Power: Turn off and lock out the field power supply feeding the POINT I/O assembly's terminal blocks if possible. While POINT I/O supports Removal and Insertion Under Power (RIUP), isolating field power prevents electrical arcing and protects sensitive logic electronics.
2. Back Up PLC Program: Connect to the controller using Studio 5000 and perform a complete upload of the running program (including tag values) to secure a known-good restore point.

Phase 2: Hardware Physical Replacement

3. Remove the Wiring Harness (RTB): Pull the orange RTB removal handle upward to unlock the Removable Terminal Block (RTB) from the base. Pull it gently away from the module. Do not disconnect the individual thermocouple wires unless replacing the base itself.
4. Remove the Module: Press down on the module lock mechanism located on the top of the module housing and slide it upward, pulling the module out of the 1734-TBCJC base.
5. Verify Keyswitch Alignment: Inspect the terminal base keyswitch. Visually confirm it is set to Position 6.
6. Insert the New Module: Align the new 1734-IT2I with the guide rails of the terminal block. Slide the module down until it clicks securely into place, engaging the DIN rail and adjacent slide-locks.
7. Reinstall the RTB: Align the RTB with the bottom of the module housing and push down until the latch clicks, securing the thermocouple wiring interface back onto the module.

Phase 3: Software and Parameter Validation

8. Restore Power and Establish Communications: Turn on power to the POINT I/O rack. Observe the module's diagnostic LEDs.
9. Check Module Status Indicators:
   • Module Status (MS): Should turn solid green (normal operation). If flashing red, a recoverable firmware or hardware fault exists.
   • Network Status (NS): Should turn solid green, indicating a connection is active with the remote Ethernet adapter (e.g., 1734-AENTR).
   • Channel Status (Ch 0 / Ch 1): Solid green indicates the channel is configured and executing normal conversions. Flashing red indicates an open-circuit (broken wire) or over/under-range condition.
10. Validate Temperature Tags: Open the Controller Tag controller monitor list in Studio 5000. Verify that the temperature inputs for both channels represent accurate, stable ambient or process values. If executing a standard replacement, no code alterations are required.

Frequently Asked Questions

Q1: Can I use a standard 1734-TB terminal base for the 1734-IT2I?

A: No. The 1734-IT2I requires reference point cold-junction compensation to calculate temperature accurately. You must use the 1734-TBCJC terminal base, which has an integrated CJC thermistor connected directly to terminals 4 and 5.

Q2: What causes a flashing red channel LED on the 1734-IT2I?

A: A flashing red light on Ch 0 or Ch 1 typically indicates a sensor fault. This is either an open-circuit hazard (such as a broken or disconnected thermocouple wire), a misconfigured thermocouple type in the module properties, or an input voltage that exceeds the designated operational range.

Q3: My temperature reading is stuck at -32768 or 32767. What is wrong?

A: These values represent underflow and overflow limits in integer math. This usually points to a broken-wire fault, a disconnected thermocouple probe, or incorrect polarity on the terminal screw connections (+ and - leads reversed).

Q4: How is the thermocouple shield wire terminated on a 1734-TBCJC?

A: Thermocouple shield wires should be terminated at a clean, low-impedance ground point (such as a copper grounding bar on the sub-panel). If grounding at the module, use a dedicated ground terminal base (e.g., 1734-TB3) adjacent to the module, or ensure the shield is terminated only at one end to prevent ground currents from running through the shield.

Related Products & Families

• 1734-TBCJC: Cold Junction Compensation Terminal Base Assembly with screw terminals.
• 1734-IR2 / 1734-IR2E: 2-channel RTD Input Modules (used when resistive temperature detectors are preferred over thermocouples).
• 1734-AENTR: Dual-port EtherNet/IP adapter for Allen-Bradley POINT I/O racks.
• 1734-FPD: POINT I/O Field Power Distributor, used to segregate field-side power configurations along the backplane.

Need Help?

Whether you are updating legacy control environments or source-replacing critical hardware components, Palm Parts Solution has you covered. We maintain a large inventory of new, refurbished, and certified surplus Allen-Bradley automation components, including the 1734 POINT I/O series. Our products are fully inspected and backed by a comprehensive warranty to ensure maximum reliability on your factory floor. Contact our technical team today to source your replacement parts or request troubleshooting assistance.