Principles Of Operation - Mitsubishi Electric JT-SB116EH-W-CA Handbook

9. Principles of operation

Description of circuit operation
(1) Cautions for turning "ON / OFF" the power switch
1 When the power switch is turned "ON", the power lamp (LED1), blue emblem lamp (LED4) and illumination
lamps (LED10, 11) turn on after 1.5 seconds, and the hand dryer becomes ready for operation.
• If the power lamp is turned off, the hand dryer does not operate even if hands are inserted in the hand
drying area. In the meantime, the microcomputer of the main unit (IC2) performs the initial setting for the
power supply frequency judgment, setting of the hand detection sensor sensitivity, and others.
• In order to set correctly the sensitivity of hand detection sensor, don't insert hands in the hand drying area
till the power lamp is turned on. (If the sensitivity is set abnormally, by neglecting this caution, for
example, an error is displayed and the operation stops. In such occasion, cancel the setting by turning off
the power switch.)
• Even if the hand dryer has started immediately after turning the power switch "ON" (less than 15
seconds), it is normal though the motor input may become slightly lower owing to the initial setting.
2 When the power switch is turned "OFF", the power lamp, blue emblem lamp and illumination lamps turn off
and the operation is inhibited.
• Circuitry takes about 30 seconds to discharge the voltage retained in them. Wait till the discharging time
elapses before plugging in or out connectors, replacing circuits, or others.
• When any error has occurred, the error display persists till the voltage retained in the circuitry is
discharged (till the microcomputer is reset).
(2) Hand detection and operation
1 Hand detection sensor is an infrared sensor assembled with the light emitting sensor (red LED), light
receiving sensor (photo-diode), etc. and consists of the upper (this side) sensor and the lower (inner)
sensor.
2 Reflection type upper sensor ... The sensor detects the change in the reflected amount of infrared when
hands are inserted. Transmission type lower sensor ... The sensor detects that the infrared is shielded
when hands are inserted.
3 As the lower sensor detects hands, the blower motor turns on and the hand dryer starts to operate.
4 Once the operation has started, it continues as long as either of upper and lower sensors detects hands.
5 If then it elapses for 1.5 to 3 seconds without detecting hands by both upper and lower sensors, the blower
motor turns off and the operation stops.
6 The hand dryer continuously operates up to 30 seconds.
• Once 30 seconds have elapsed, the hand dryer stops operating even if hands are detected.
• Since this is a function to override the presence of foreign object, the operation starts if hands are pulled
out and inserted again.
(3) Control of the blower motor
1 DC brushless motor is used for the blower. This motor has no hole sensor to detect the rotor position, but
utilizes instead the counter electromotive voltage by the motor coil to judge the rotor position and the
revolving direction so as to drive the motor.
2 Outputs from the motor control microcomputer (IC1) are transmitted via the drive IC (IC3) to control the
power step MOSFET (driving transistor) that drives the motor.
— 17 —