1734-IR2 RTD Input Module Replacement

Overview

The Allen-Bradley 1734-IR2 is a 2-channel, 16-bit Resistance Temperature Detector (RTD) input module within the POINT I/O product line. It translates analog resistance variations from temperature sensors into digital proportional values for use by Logix controllers via EtherNet/IP, ControlNet, or DeviceNet adapters.

Industrial automation systems frequently run these modules continuously for over a decade. Over time, environmental stressors such as thermal cycling, vibration, or voltage spikes can degrade the internal Sigma-Delta analog-to-digital converter (ADC) or damaged contact blades on the POINTBus connector, requiring module replacement. This guide details the specifications, compatibility rules, wiring conventions, and step-by-step procedures for replacing a damaged or legacy 1734-IR2 module to minimize system downtime.

Legacy Product Information

The 1734-IR2 is a highly compact, 12mm-wide slice module. Since its launch, it has gone through several physical and hardware revisions (commonly known as Series A, B, and C). While older Series A and B modules are no longer actively manufactured by Rockwell Automation, the 1734-IR2 Series C remains an active product catalog number.

Specifications & Parameters:

• Analog Inputs: 2 single-ended channels (non-isolated from each other, isolated from backplane).
• Supported Sensors: Platinum (100, 200, 500, 1000 $Omega$ with 385 or 3916 curves); Nickel (120 $Omega$ with 672 curve); Copper (10 $Omega$ with 427 curve).
• Resistance Range: 0 to 600 $Omega$.
• ADC Resolution: 16-bit (signed integer or 2's complement).
• POINTBus Current Consumption: 220 mA @ 5V DC.
• Power Dissipation: 1.0 W maximum @ 28.8V DC.
• Data Formats: Engineering units (0.1°C or 0.1°F), Percent of Full Scale, Raw Proportional, or Scaled-for-PID.
• Excitation Current: 1.0 mA typ.

Typical Applications:

• Temperature monitoring in plastics extrusion barrels.
• HVAC air duct and chiller loop management.
• Boiler feedwater and steam temperature measurement.
• Food and beverage pasteurization loops.

Recommended Replacements

When a 1734-IR2 module fails, several migration paths are open to control engineers, depending on system performance targets and configuration baselines:

Compatibility Considerations

Replacing a 1734-IR2 module with a newer revision within the POINT I/O platform is highly straightforward, but several platform-specific requirements must be followed:

1. Wiring & Removable Terminal Block (RTB) Alignment

The 1734-IR2 mounts onto a 1734-TB, 1734-TBS, 1734-TOP, or 1734-TOPS terminal base assembly. The RTD wires connect directly to this base, meaning you do not need to rewrite terminal connections during module replacement.

• 2-Wire RTDs: Connect to L1 (Sense) and L2 (Source/Return) terminals. Must jump L2 and L2 Return at the terminal base.
• 3-Wire RTDs: Connect L1 (Sense) to Terminal 0 (Ch 0) or Terminal 4 (Ch 1); L2 (Source) to Terminal 1 (Ch 0) or Terminal 5 (Ch 1); and L2 Return to Terminal 2 (Ch 0) or Terminal 6 (Ch 1).

2. Physical Footprint & Keying

Every POINT I/O base has a mechanical, rotary keyswitch. For the 1734-IR2, the keyswitch must be rotated to Position 6. This prevents an incorrect module type (such as a 120V AC output) from being accidentally inserted into the slot and damaging field sensors or backplane electronics.

3. Software & Firmware Compatibility

If replacing an older Series A or B module with a newer Series C module, the controller software (RSLogix 5000 / Studio 5000 Logix Designer) might report an I/O connection fault:

• Electronic Keying: If the original module module profile in the I/O configuration is set to "Exact Match", the controller will reject the new Series C module if it was configured for a Series B.
• Correction: Change the Electronic Keying in the module's controller properties window to "Compatible Module" or "Disable Keying". Alternatively, upload the latest Add-On Profile (AOP) for the 1734-IR2 Series C into your programming environment.

Upgrade Benefits

Upgrading from older Series A or B modules to the current 1734-IR2 Series C revision brings several operational benefits:

• Improved Noise Rejection: Modern assembly revisions feature refined onboard filters, offering higher ambient electromagnetic interference (EMI) blocking for low-signal millivolt RTD lines.
• Enhanced Thermal Dissipation: Internal electronic components feature improved thermal efficiency, allowing the module to run cooler inside densely populated control cabinets.
• Stable Lead-Wire Compensation: Series C modules feature tighter tolerances inside the current excitation circuit, ensuring that resistance measurements remain highly accurate over longer field-cable distances.
• Robust Housing: The mechanical slide lock and DIN-rail attachment mechanisms are constructed with stronger polymers to resist degradation and breakage from continuous machine vibration.

Common Migration Challenges

System integration engineers replacing a 1734-IR2 module typically encounter three primary issues:

• I/O Fault Code 16#0114 (Electronic Keying Mismatch): This occurs if the controller PLC profile is expecting a legacy hardware revision. If you cannot go online to change the configuration parameters, you must source a matching remanufactured Series B module to keep the PLC configuration intact.
• Offset Errors (Temperature Offsets of 20°C to 50°C): This is usually caused by swapping to a standard 1734-IR2 and failing to properly configure the exact RTD curve (PT385 vs. PT3916). Ensure the software profile configuration properties match the physical RTD probe specification sheet.
• Open Sensor Faults (Flashing Red Channel LED): This is caused by loose field-wiring connections at the terminal base or a broken lead-wire compensator link on 3-wire RTD sensors.

Step-by-Step Replacement Procedure

Follow these steps to safely and efficiently replace an existing 1734-IR2 module:

Step 1: Safety & Isolation

1. Confirm the plant/process is in a safe state to interrupt temperature signal monitoring.
2. Isolate internal cabinet power. Turn off the main field power supply feeding the POINT I/O network adapter (e.g., 1734-AENT/AENTR) to prevent hot-swap arcs, although the POINT I/O modules support "Removal and Insertion Under Power" (RIUP) under non-hazardous, safe-atmosphere conditions.

Step 2: Remove the Removable Terminal Block (RTB)

1. Pull up the orange RTB pull ring or press in the wiring latch (depending on the base model used).
2. Swing the RTB block upward and pull it gently out of the module slot. Set it aside with the field wiring bundle intact.

Step 3: Remove the Damaged 1734-IR2 Module

1. Locate the orange lock slider on the top of the 1734-IR2 module housing.
2. Push this locking mechanism forward (away from the DIN rail) to release the POINTBus interconnect.
3. Pull the module straight out of the mounting base sliding it upwards along the interlocking guide rails of the adjacent module.

Step 4: Verify Base Keying and Condition

1. Inspect the terminal base contact blades for corrosion, dust, or bent elements. Clean if necessary.
2. Verify that the mechanical keyswitch on the terminal base is pointing to Position 6.

Step 5: Install the New 1734-IR2 Module

1. Position the replacement module on the guide rails above the empty terminal base slot.
2. Slide the module down until it is resting firmly inside the mounting base.
3. Push the orange lock slider back (towards the DIN rail) until it snaps, locking it securely into the POINTBus.

Step 6: Install the Removable Terminal Block (RTB)

1. Insert the lower pivot edge of the RTB back into the terminal base.
2. Press down firmly on the top of the block until the unit clicks into place on the module body.

Step 7: Power-Up & Diagnostics Verification

1. Apply control power to the POINT I/O assembly.
2. Observe the Module Status (MS) LED: It should light solid green.
3. Observe the Network Status (NS) LED: It should light solid green, indicating established communication with the main PLC.
4. Check the Channel 0 and Channel 1 LEDs:
   • Solid Green: Sensor normal, measuring in-range resistance.
   • Flashing Red: Bad wiring/input, open circuit, or unconfigured channel. Ensure configuration has been downloaded successfully from the controller.

Frequently Asked Questions

Q1: Is the 1734-IR2 module capable of reading 4-wire RTDs?

A1: Yes, but the module does not have dedicated terminals for a 4th wire. To use a 4-wire RTD, you must convert it into a 3-wire hookup. To do this, connect the primary two leads to Terminals 0 and 1, the third lead to Terminal 2, and cleanly insulate and secure the fourth wire so it does not make electrical contact.

Q2: What is the difference between the 1734-IR2 and the 1734-IR2E?

A2: The 1734-IR2E was a specialty version designed for extrusion/injection molding systems. It featured a slightly modified temperature range scaling capability in the analog register. For modern systems, the standard 1734-IR2 Series C supports comparable temperature curve configurations and serves as the primary replacement.

Q3: Why is my channel LED flashing red after replacing the module?

A3: A flashing red channel LED indicates an out-of-range signal or open sensor circuit. Ensure that the RTD sensor wiring is secure inside the terminal base clamps and that the RTD type and measurement rate configured in Studio 5000 match the physical sensor and process requirements.

Q4: Can I complete the hardware exchange while the PLC package is running?

A4: Yes, the POINT I/O system supports Removal and Insertion Under Power (RIUP). However, the field loop power and signal to that specific slot will be disrupted, which can cause the controller to record an I/O connection fault. It is highly recommended to place the PLC or associated PID loop into "Manual" or "Program" mode before replacement.

Related Products & Families

• 1734-TB / 1734-TBS: Wiring terminal bases used to host POINT I/O slices.
• 1734-IT2I: Isolated 2-Channel Thermocouple Input Module.
• 1734-IE2C / 1734-IE2V: 2-Channel Analog Current/Voltage Input Modules.
• 1734-AENTR: Dual-port EtherNet/IP POINT I/O Adapter.

Need Help?

Dealing with obsolete hardware configurations or unexpected keying mismatches? Palm Parts Solution can supply new, surplus, or rigorously tested refurbished 1734-IR2 modules to fit any budget. All of our units are backed by a complete warranty to get your industrial systems up and running securely. Contact our North American support team today for technical advice or a quote on replacement parts.