What is the primary function of a thermistor in a 3D printer hot end?

The primary function of a thermistor in a 3D printer hot end is to accurately measure the temperature of the hot end. A thermistor is a type of resistor whose resistance changes significantly with temperature. In a 3D printer, the thermistor is typically embedded in the heat block of the hot end, and its resistance is continuously monitored by the printer's control board. The control board uses the thermistor's resistance reading to determine the hot end temperature and then adjusts the power supplied to the heater cartridge to maintain the desired temperature. This closed-loop feedback system is essential for precise temperature control, which is critical for successful 3D printing. Without accurate temperature measurement from the thermistor, the printer would be unable to maintain the correct temperature for melting and extruding the filament, leading to print failures.