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Key Technical Specifications (For Spare Part Verification)
- Product Model: SCXI-1325
- Manufacturer: National Instruments
- Compatible Module: SCXI-1125 (8-channel isolated thermocouple input)
- Terminal Type: Screw-terminal block with isothermal design
- Cold Junction Sensor: Integrated precision thermistor for CJC
- Channel Count: 8 differential thermocouple inputs + CJC reference
- Connector Interface: Direct mating with SCXI-1125 front connector
- Operating Temperature: 0 to 55 °C (standard industrial range)
- Material: Thermally conductive housing to ensure uniform block temperature
- Certification: CE, FCC; compatible with IEC 61010 safety standards at time of manufacture
- Physical Dimensions: Matches SCXI 1U form factor (standard width for SCXI modules)
NI SCXI-1325
System Role and Downtime Impact
The SCXI-1325 is not a standalone module but an essential mechanical and thermal interface that attaches directly to the SCXI-1125 signal conditioning card inside an SCXI chassis. It provides the physical terminals for thermocouple wiring and houses the cold junction sensor critical for accurate temperature measurement—especially in applications like engine testing, environmental chambers, and process monitoring.
If the SCXI-1325 is damaged, corroded, or unavailable during maintenance, the SCXI-1125 cannot deliver calibrated readings. Even minor thermal gradients across the terminal block introduce significant measurement errors (±2–5 °C or more). Replacement requires exact compatibility; generic terminal blocks lack CJC integration and isothermal properties. Without a verified spare, recalibration or system downtime may be required, disrupting long-duration tests or continuous monitoring operations.
Reliability Analysis and Common Failure Modes
While passive in design, the SCXI-1325 is subject to field-induced degradation:
Screw terminals loosen over time due to vibration or thermal cycling, increasing contact resistance and causing intermittent signals. Corrosion from ambient humidity or chemical exposure degrades thermocouple junctions, especially with dissimilar metals (e.g., Type K in high-sulfur environments). The embedded thermistor can drift due to aging or localized heating from nearby power modules, skewing CJC calculations. Additionally, plastic housing may crack if over-torqued during wire installation, compromising thermal uniformity.
Preventive maintenance recommendations include:
- Performing periodic torque checks on terminal screws (use manufacturer-specified values)
- Inspecting for green/white corrosion on copper terminals, particularly in harsh environments
- Verifying CJC accuracy during system calibration using a reference thermometer
- Storing spares in dry, static-safe packaging to prevent moisture absorption
NI SCXI-1325
Lifecycle Status and Migration Strategy
National Instruments officially discontinued the entire SCXI platform, including the SCXI-1325, as it shifted focus to CompactDAQ and PXI-based architectures. Emerson (current owner of NI) offers no new units, repairs, or cross-reference alternatives.
Short-term mitigation:
- Secure multiple SCXI-1325 units from trusted surplus vendors with visual and functional verification
- Maintain detailed photos and wiring diagrams for rapid reconnection
- Use protective terminal covers when systems are idle to reduce oxidation
Long-term migration path:
- Replace SCXI-1125 + SCXI-1325 with NI 9211 or NI 9213 modules in a CompactDAQ chassis—both offer integrated CJC, higher channel density, and USB/Ethernet connectivity
- For high-channel-count or rack-mounted needs, migrate to PXIe-4353 in a PXI Express system with superior noise immunity and faster sampling
- Leverage NI’s DAQmx driver compatibility to minimize software rework during transition
