How should thermocouple placement be specified for industrial heating elements?

Place the thermocouple where it senses the real temperature of the load or workpiece, not against the element sheath: too close and it reads radiant heat plus contact resistance, giving a high, unstable reading; too far and it lags the actual condition. Before purchase, fix insertion depth and location by furnace zone and airflow path, matched to power, tube diameter, watt density, sheath material and protection rating, and select thermocouple type, wire gauge and response time accordingly. Mount it with a heat-resistant sleeve or bracket, keep it off the element, and route terminals away from hot zones. Verify representativeness with multi-point temperature records, and agree on deviation limits, calibration intervals and acceptance conditions in the specification with the supplier.