How to Determine Sensor Insertion Depth

Overview

Insertion depth decides whether the sensor reads the process temperature or the temperature of the pipe wall and lining. Too shallow, and heat conducted along the sheath pulls the reading towards ambient.

Key Points

Rule of thumb for liquids and gases. Immerse at least 8–10 times the sheath diameter beyond the inner wall, and place the tip near the centre of the flow.
For solid linings. The tip must pass through the lining into the medium; calculate from the lining thickness plus the nozzle length.
Avoid dead zones. Do not mount in a stagnation pocket or immediately behind a bend.
Check mechanical limits. High-velocity flow can vibrate a long, unsupported sheath — verify with a wake-frequency calculation.

Summary

Record the required immersion length on the drawing together with the nozzle length, so the sensor and the thermowell are ordered as a matched set.

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