Unbalanced Load Detection - Bosch WAT28400 Repair Instructions

Design and function
3.11

Unbalanced load detection

Unbalance occurs in rotating bodies whose mass is not distributed in a rotationally
symmetrical manner. The loaded drum of a washing machine always experiences
unbalance, as the laundry items are never optimally distributed around the axis of
rotation. If the unbalance cannot be offset by the oscillating system of the washing
machine, damage to the appliance and its installation location may occur.
The unbalanced load detection monitors unbalance in the drum during the spin
cycle start-up. If an unbalance occurs which is too high, the control unit reduces
the rotary speed of the drum. Damage caused by high unbalance is avoided in this
way. In order to measure the unbalance, the motor is accelerated to a constant
rotary speed for a specific time period. Appliances in newer model series measure
unbalance at various rotary speeds. The multilevel unbalance detection is more
accurate and ensures that the unbalance limit value provided is not exceeded for
the spin speed selected.
There are various procedures for measuring the unbalance:
• Determination of asynchronous motor operating values
• Determination of the drum deviation
Appliances with 3D/3G sensor determine the unbalance before acceleration to
the spin speed in 3 consecutive measurements.
2017-05-22 / DIS 113_58300000186503_ara_en_c
Fig. 15: Unbalance measurement process schematic with 3D/3G sensor
A Measurement 1
B Measurement 2
C Measurement 3
Mea- Measurement
sure system
1 Motor tachome-
ter
2 3D/3G sensor
3 3D/3G sensor
Table 4: Measurements
If measurement 1 or 2 determines an impermissible unbalance, the control unit
reduces the rotary speed of the drum in order to improve the distribution of the
laundry. Then, measurement 1 is restarted.
A maximum total of 15 start-ups to the rotary speed are possible for measurements
1 and 2. For the wool wash programme, unbalance recognition is limited to 2 start-
up attempts.
Copyright by BSH Hausgeräte GmbH
D Duration of measurement 2
E Duration of measurement 3
F Decreased rotary speed after start-up attempt
Measurement Duration of
rotary speed measurement
100 rpm 20 seconds
180 rpm 10 seconds
600 rpm 10 seconds
Measured
quantity
Rotary speed
fluctuation
Maximum ampli-
tude of the oscil-
lating system
Maximum ampli-
tude of the oscil-
lating system
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