Allen-Bradley 1794-IRTB – RTD/Resistance Input Module | FLEX I/O Platform
Engineering Background
The 1794-IRTB is part of Rockwell Automation’s FLEX I/O family — a modular, distributed I/O platform engineered for demanding industrial environments. FLEX I/O was designed to bridge field-level sensing with plant-wide control networks, offering compact form factor without sacrificing channel density or signal fidelity. The 1794-IRTB specifically addresses precision temperature and resistance measurement, a critical requirement in process industries where thermocouple drift or sensor degradation can cause costly production deviations.
Product Positioning
The 1794-IRTB is the preferred RTD/resistance input solution for engineers integrating FLEX I/O into ControlLogix, CompactLogix, or legacy PLC-5/SLC 500 architectures via 1794 adapter modules. It delivers 8-channel simultaneous RTD or resistance measurement with high-resolution A/D conversion, making it suitable for both continuous process monitoring and discrete temperature interlocking applications. At Konmask.com, this module is sourced from verified industrial surplus channels and undergoes functional inspection prior to dispatch.
Complete Technical Specifications
- Catalog Number: 1794-IRTB
- Manufacturer: Allen-Bradley / Rockwell Automation
- Platform: FLEX I/O (1794 Series)
- Module Type: RTD / Resistance Input
- Number of Input Channels: 8 (differential)
- Supported Sensor Types: Pt100, Pt200, Pt500, Pt1000 (IEC 60751 / DIN 43760), Ni120, Cu10; 3-wire and 4-wire RTD configurations; raw resistance (0–3000 Ω)
- Measurement Resolution: 16-bit A/D conversion
- Temperature Range: –200 °C to +870 °C (sensor-dependent)
- Accuracy: ±0.1 °C typical (Pt100, 0–100 °C range)
- Input Impedance: >1 MΩ
- Excitation Current: 1 mA (constant current source per channel)
- Backplane Current Draw: 75 mA @ 5 VDC
- Power Dissipation: 0.375 W (max)
- Operating Temperature: 0 °C to +60 °C
- Storage Temperature: –40 °C to +85 °C
- Relative Humidity: 5–95% non-condensing
- Vibration: IEC 68-2-6 compliant
- Shock: IEC 68-2-27 compliant
- Agency Certifications: UL Listed, CE Marked, C-Tick
- Enclosure Rating: Open-style (requires enclosure installation)
- Dimensions (H × W × D): 94 mm × 23 mm × 87 mm
- Weight: ~100 g
- Wiring: Removable terminal block (RTB), 20-position
- Communication: Via 1794 adapter (ControlNet, DeviceNet, EtherNet/IP, RIO, DH+)
Proven Application Environments
- Oil & Gas: Pipeline temperature monitoring, heat exchanger control, wellhead RTD integration
- Chemical Processing: Reactor temperature profiling, distillation column monitoring, exothermic process interlocking
- Food & Beverage: Pasteurization temperature validation, CIP cycle monitoring, cold-chain compliance logging
- Pharmaceutical: Autoclave validation, cleanroom HVAC temperature control, FDA 21 CFR Part 11 compliant data acquisition
- Power Generation: Turbine bearing temperature monitoring, transformer winding temperature protection
- Water & Wastewater: Effluent temperature monitoring, digester process control
- HVAC / Building Automation: Multi-zone temperature acquisition integrated with ControlLogix BAS architectures
Engineering Advantages
- Multi-Sensor Flexibility: Single module supports Pt100/Pt200/Pt500/Pt1000/Ni120/Cu10 and raw resistance — eliminates need for separate modules per sensor type
- High Channel Density: 8 differential channels in a 23 mm wide FLEX I/O slot — maximizes panel real estate in distributed I/O racks
- 16-Bit Resolution: Delivers ±0.1 °C accuracy typical, suitable for precision process control without external signal conditioning
- Open-Wire & Short-Circuit Detection: Built-in diagnostics flag sensor faults directly in the controller tag database — reduces MTTR
- Hot-Swap Capable: FLEX I/O architecture supports module replacement under power (adapter-dependent) — minimizes planned downtime
- Adapter-Agnostic: Compatible with all 1794 adapter modules (ControlNet, DeviceNet, EtherNet/IP, RIO, DH+) — future-proofs network migration
- Removable Terminal Block: RTB wiring survives module swap without rewiring — critical for maintenance efficiency
System Architecture & Signal Flow
The 1794-IRTB mounts on a 1794 terminal base unit (TBU) and communicates via the FLEX I/O backplane to a 1794 adapter module. The adapter bridges the I/O data to the plant control network (ControlNet, DeviceNet, EtherNet/IP, etc.), where a ControlLogix or CompactLogix controller reads channel data as structured tags in the I/O tree.
Signal path: RTD sensor → 3/4-wire field wiring → 1794-IRTB terminal block → 16-bit A/D conversion → FLEX I/O backplane → 1794 adapter → control network → controller tag (REAL, °C or Ω) → HMI / historian / interlock logic.
Each channel produces a floating-point engineering-unit value (°C or Ω) directly in the controller — no scaling rungs required in ladder logic. Fault bits (open wire, short, over/under range) are exposed as individual BOOL tags per channel.
Sourcing & Quality Verification
- All 1794-IRTB units at Konmask.com are sourced from verified industrial surplus, OEM overstock, or authorized distribution channels
- Each unit undergoes visual inspection for physical damage, label integrity, and connector condition prior to listing
- Firmware revision and hardware revision are documented where available
- Original Rockwell Automation packaging preserved where possible
- Traceability documentation available upon request for regulated industries (pharma, nuclear, defense)
- All units ship with ESD-protective packaging
Procurement Process
- Step 1 – Confirm Part Number: Verify catalog number 1794-IRTB and hardware/firmware revision requirements with your controls engineer
- Step 2 – Request Quote: Contact [email protected] with quantity, required delivery date, and any revision constraints
- Step 3 – Order Confirmation: Purchase order accepted via email; proforma invoice issued within 1 business day
- Step 4 – Inspection & Dispatch: Unit inspected, photographed, and dispatched with tracking within 2–3 business days
- Step 5 – Incoming Inspection: Recommended: perform functional bench test on arrival before installation in live system
- Lead Time: In-stock units ship within 3 business days; out-of-stock sourcing typically 7–15 business days
- Payment: T/T bank transfer, PayPal, and major credit cards accepted
Technical FAQ
Q: Can the 1794-IRTB be used with 2-wire RTDs?
A: Rockwell recommends 3-wire or 4-wire RTDs for best accuracy. 2-wire configurations are possible but introduce lead resistance error — not recommended for precision applications.
Q: Which terminal base unit (TBU) is required?
A: The 1794-IRTB requires the 1794-TB3 or 1794-TB3S terminal base. Confirm TBU availability when ordering.
Q: Is the 1794-IRTB compatible with ControlLogix via EtherNet/IP?
A: Yes — pair with a 1794-AENT or 1794-AENTR adapter for EtherNet/IP connectivity to ControlLogix or CompactLogix systems.
Q: What is the scan time per channel?
A: Typical channel update rate is approximately 150 ms per channel (all 8 channels = ~1.2 s full scan). For faster scan requirements, consider the 1794-IR8 (4-channel, faster update).
Q: Can I mix RTD types on the same module?
A: Yes — each channel is independently configurable for sensor type via the module configuration in RSLogix 5000 / Studio 5000.
Q: Do you provide a warranty?
A: Konmask.com offers a 90-day functional warranty on all surplus modules. Extended warranty available upon request.
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