Mineral-Insulated Thermocouple: Installation Notes

Overview

A mineral-insulated (MI) thermocouple is supplied as a fully assembled, bendable cable. Most premature failures are caused during installation — over-tight bending, sealing that lets moisture in, or a mounting that puts the cable in tension.

Key Points

Observe the minimum bend radius. Bending tighter than roughly five times the sheath diameter can crack the MgO insulation.
Keep the terminal head dry. Moisture in MgO collapses the insulation resistance; seal the cold end and use a gasketed head outdoors.
Support the cable. Do not let the weight of the cable or vibration load the measuring junction.
Match the insert depth. The tip must sit in the process medium, not in the nozzle or lining.

Summary

After installation, check the insulation resistance at room temperature and record it as a baseline. A later drop against that baseline is the earliest and most reliable sign that the sensor is degrading.

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