Please make sure that the external sensor has contact with the soldered PCB. Due to the thermal inertia of the PCB, the sensor should not be placed over copper planes. It can be on a pad if that pad is not covered with solder paste (otherwise soldering will damage the sensor). Best it is placed on the solder mask free from copper underneeth (if this is not possible and heavy copper is there, you might need to adjust the temperature correction factor – see temperature correction.).
Sensor placed correctly on the PCB
Sensor not correctly placed – not touching
The graphic lines of the sensors should look seamless. Steep and unexpected variations in measurements mean measurement errors.
Graph showing seamless lines
Line variations for the furnace and bottom heater are not possible, due to the construction of the sensors. When the external sensor line shows variations then it is possible that the sensor makes no or a bad contact with the PCB.
A ragged line means a bad contact.
Graph showing lines not seamless
For fixing of the external sensor we recommend an adhesive Capton tape.