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12-02-2003
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51
When the maximum number of activated dots is 128 dots, and all of the
dots are driven, as shown in
2.7.3 Head Control Circuit
The PRN604-S has a function for measuring the resistance of the
thermal head connected to the FTP604.
The PRN604-S measures the resistance of the thermal head and
detects the errors at initialisation.
Based on the measurement, the PRN604-S determines how much
energy to apply. No adjustment is needed for replacing the FTP604 to
get the best printing.
2.7.4 Head temperature measurement circuit
The thermistor is mounted on the FTP604 to measure the temperature
of the thermal head.
The PRN604-S determines the energy to be applied to the head and
also checks for head temperature errors.
If the temperature of the thermal head is -10 °C or lower, or 80 °C or
higher, the PRN604-S stops driving and puts the printer in head
temperature error status. If the temperature of the thermal head is
returned to from -5 °C to 75 °C, the printer goes to printable status.
2.7.5 Vhead interrupt circuit
This circuit interrupts Vhead to prevent electrolytic corrosion of the
thermal head and to enable the detection of the resistance mentioned
above.
Electrolytic corrosion may significantly shorten the life of the thermal
head. Thermal paper ordinarily contains electrolytic material to prevent
sheets from sticking to each other due to static electricity. If there is too
much of this electrolytic material, high temperatures and humidity cause
the material to ionise, resulting in electrolytic corrosion of the thermal
head.
The PRN604-S turns the FET off and breaks the Vhead applied to the
thermal head during waiting status to prevent electrolysis corrosion of
the thermal head.