◦
Current detection circuit
◦
Thermoswitch
●
DC controller: The DC controller monitors the detected temperature of the main thermistor and
sub thermistors. The DC controller deactivates the FIXING HEATER CONTROL signal and
releases the relay to interrupt power supply to the fuser heater under the following conditions:
◦
TH1: 230° C (446° F) or higher
◦
TH2: 285° C (545° F) or higher
◦
TH3: 285° C (545° F) or higher
●
Fuser-heater safety circuit: The fuser heater safety circuit monitors the detected temperature of
the sub thermistors. The fuser heater safety circuit releases the relay to interrupt power supply to
the fuser heater under the following conditions:
◦
TH2: 290° C (554° F) or higher
◦
TH3: 290° C (554° F) or higher
●
Current-detection protection circuit: The current detection circuit monitors the current flowing
through the fuser heater control circuit. The current detection circuit deactivates the fuser heater
control circuit to interrupt power supply to the fuser heater when it detects the current higher than
a specified value.
●
Thermoswitch: If the temperature in the heaters is abnormally high, and the temperature in the
thermoswitches exceeds a specified value, the contact to the thermoswitch breaks. Following are
the thresholds for each thermoswitch:
◦
TP1: 270° C (518° F) or higher
NOTE: When the thermoswitches reach this temperature, the temperature on the fuser rollers is about
320° C (608° F).
Failure detection
The DC controller determines a fuser unit failure, deactivates the FIXING HEATER CONTROL signal,
releases the relay to interrupt power supply to the fuser heater, and notifies the formatter of a failure
status when it encounters any of following conditions:
●
Abnormally high temperatures: Temperatures are too high for any of the following components,
at any time:
◦
TH1: 230° C (446° F) or higher
◦
TH2: 285° C (545° F) or higher
◦
TH3: 285° C (545° F) or higher
●
Abnormally low temperatures: Temperatures are too low at any of the following components
after the product has initialized.
◦
TH1: 120° C (248° F) or lower
◦
TP2 or TP3: 100° C (212° F) or lower
●
Abnormal temperature rise: The DC controller determines an abnormal temperature rise if the
detected temperature of TH1 does not rise 2° C within a specified time after the fuser motor is
16 Chapter 1 Theory of operation ENWW
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