| 摘要 |
PURPOSE:To detect temp. abnormality in a short period by providing a means for detecting a temp. change which detects the temp. change for the prescribed time by a temp. detecting sensor and a means for forming a temp. abnormality signal when the detected temp. change exceeds the preset value. CONSTITUTION:The surface temp. of a heater roller 1 detected by a thermistor Rth is converted to a voltage which is outputted to a temp. control circuit CT. The control circuit controls the on and off of a heater lamp HL in such a manner that the detected temp. is included in the range of control temps. theta1, theta2. A sample holding circuit SH1 samples and holds the output voltage of the thermistor when a switch SW3 for detecting the passage of paper turns off. A sample holding circuit SH2 samples and holds the output voltage of the thermistor when a timer T times up. The output voltage V2 of the circuit SH2 is dropped to a voltage V2' by a constant voltage dropping circuit consisting of a combination of a resistor R1 and a Zener diode ZD. The low- noise abnormality signal of 'H' is formed if the input voltage V1 from the circuit SH1 is larger than another input voltage V2'. |
