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3.6.7 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:
z Detecting abnormal temperatures by software
Design software that will deactivate the heat elements if the thermal head thermistor (TH)
detects a temperature of 80°C or more (thermistor resistance RTH ≤ 3.80 kΩ), and reactivate
the heat elements when a temperature of 60°C or lower (RTH ≥ 7.45 kΩ) is detected. If the
thermal head continues to be activated at a higher temperature than 80°C, the life of the
thermal head may be shortened significantly.
z 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. The 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 (this may not prevent damage to the thermal head).
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 ≤ 2.09 kΩ))
(b) Faulty thermistor connection (the thermistor may be open or short-circuited).
If (a) and (b) detected, immediately deactivate the heat elements. Reactivate the heat
elements after they have returned to normal.