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3.6.10 Detecting Abnormal Temperatures of the Thermal Head
To protect the thermal head and to ensure personal safety, abnormal thermal head temperatures must be
detected by both hardware and software as follows:
Detecting abnormal temperatures by software
Design software that will deactivate the heat elements if the thermal head thermistor (TH) detects
a temperature higher than 80 °C (thermistor resistance RTH ≤ 2.48 kΩ), and reactivate the heat
elements when a temperature lower than 60 °C (RTH ≥ 4.46 kΩ) is detected. If the thermal head
continues to be activated at a temperature higher than 80 °C, the life of the thermal head may be
shortened significantly.
Detecting abnormal temperatures by hardware
If the control unit (CPU) malfunctions, the software for detecting abnormal temperatures may not
function properly, resulting in overheating of the thermal head. Overheating of the thermal head
may cause damage to the thermal head or cause skin burns.
Always use hardware in conjunction with software for detecting abnormal temperatures to ensure
personal safety. (If the control unit malfunctions, it may be impossible to prevent damage to the
thermal head even if a detection of abnormal temperature is detected by hardware.).
Using a window comparator circuit or similar detector, design hardware that detects the following
abnormal conditions:
(a) Overheating of the thermal head (approximately 100 °C or higher (RTH ≤ 1.47 kΩ)).
(b) Faulty thermistor connection (the thermistor may be open or short-circuited).
If (a) and (b) are detected, immediately deactivate the heat elements. Reactivate the heat
elements after they have returned to normal.
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