How should sensor placement be specified for commercial heating elements?

Specify the sensor location where it reads the true medium temperature while staying clear of the element's local hot zone: too close to the sheath reads high because radiation and conduction add up, while too far lags in response and causes wider control swings. First define whether the medium is static or flowing, plus flow rate and direction, then weigh wattage, sheath diameter and material, surface load, protection class, mounting space, and control type, whether mechanical or electronic and whether PID is used. Fit temporary probes at several candidates, such as the return inlet, mid-tank, and near the workpiece, and log heat-up curves and steady-state error, comparing overshoot and recovery time under different loads. Choose the point with the smallest deviation and sensible response, then verify at acceptance how far it differs from the bulk medium temperature.