FISHER & PAYKEL _ DEIX1 AA WW _ INTUITIVE DRYER _ HEATER CONTROL & AUTO SENSING - PRINCIPLES
HEATER CONTROL
- The heaters are controlled in response to the selected drying cycle chosen and also according to other operational requirements such as reversing and over heating.
- The heater housing is fitted with two elements that supply approximately 5 kW of heat when both are on. There is a 3.6kW and a 1.4Kw element that are used at various times depending on the cycle chosen and the drum/fan direction.
- When drying, the heater is only switched on when the drum is up to speed. Because of the time it takes for the element to cool down after switching off, the larger element in the electric model is switched off a few seconds before stopping to reverse, to prevent excessive heat entering the drum.
- The software in the motor control module responds to the switching on and off of the heater as requested by the sensor module. It also monitors the automatic thermostat on the heater housing for excessive restriction of airflow, and if detected, will set a User Warning but continue the drying cycle until the end of the cycle when the warning will reset. If the User Warning occurs, the drying will take a longer time to complete and the load will possibly end up a little damp.
- Each cycle has a temperature limit, as measured in the exhaust air. After switching off at the limit, the temperature has a hysteresis of 5 degrees below these temperatures when the heat source switches back on. Note: During heating, if the temperature exceeds the limits for the particular cycle, the heat is turned off and can significantly reduce the heating time.
Cycle times can be affected by a
number of factors including:
- The cycle chosen
- Load size
- Size of items
- Type of fabric
- Load wetness
- Venting method
- Location of dryer
- Condition of exhaust ducts
- Environmental conditions (temperature, humidity, etc)
AUTO SENSING
When wet or damp clothes are loaded
into a dryer they are partially saturated with water which is a relatively good
conductor of electricity. In the IntuitiveTM dryer,
sensor bars (located beneath the lint bucket) are used to measure the conductivity.
When moisture in the clothes touches across the
sensor
bars their conduction is measured. As the clothes dry they become less
conductive and it is this measurement that is used to calculate the dryness of
the clothes load.
Large loads will brush against these sensor bars
more frequently than small loads, and this strike count is used to help
determine the dryness of different sized loads.
Different fabrics retain moisture differently; a
thick towel containing a lot of moisture will often conduct the same as a light
synthetic garment containing very little. It is this difference in fabric
characteristics plus the initial unknown moisture content that makes the
calculation of dryness reasonably complex.
