Fuser over temperature protection
To protect the fuser from excessive temperatures, the product has four layers of protective functions. If
one function fails, the subsequent functions should detect the problem.
●
DC controller: When a thermistor or thermopile detects a temperature above a certain threshold,
the DC controller interrupts power to the specific heater. Following are the thresholds for each
component:
◦
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: If the DC controller fails to interrupt the power to the heaters at the
prescribed temperatures, the fuser heater safety circuit deactivates the triac-drive circuit and
releases the relay, which causes the heaters to stop at slightly higher temperature thresholds.
◦
TH2: 290° C (554° F) or higher
◦
TH3: 290° C (554° F) or higher
●
Current detection protection circuit: If current flowing in each triac exceeds a specific value,
the current detection protection circuit deactivates the triac-drive circuit and releases the relay,
which interrupts the power supply to the heaters.
●
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. Breaking this
contact deactivates the triac-drive circuit and releases the relay, which interrupts the power supply
to the heaters. 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).
ENWW
Engine control system
17
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