GV 640 Service Manual 13
For internal use only
4.2 Control module Piezo keys
Appliances with Piezo keys have a flat control panel. The stainless steel control interface reacts to even
the slightest touch. This is because of a control button fitted with minute crystal elements that has been
applied with glue. The electrical impulses are generated according to the principle of Piezo technology.
4.2.1 Piezo electric principles
Mechanical pressure generates an electrical charge on certain crystals, also called Piezoelectric ceram-
ics. Natural crystals only show this effect to a very limited extent, e.g. Turmalin. Lead zirconate titanate
as a natural crystal is doped by foreign atoms. This enhances the Piezo effect.
This crystalline property was discovered by the physicists Pierre and Marie Curie in 1880. The name
“Piezo” has its origins in the Greek language and means “pressure” or “press”. Electrical voltages can
be determined on two crystal surfaces when pressure changes. This change in pressure may result from
bending, turning or pressing. The electrical voltage is proportionate to the power exerted.
A hexagonal crystal structural cell is shown here. This cell is externally neutralised elec-
trically, since all the charges have been equalised.
The centre of gravity of the positive and negative charges are forced against one another
under pressure.
A difference in charge will result. This is tapped as a charge or voltage and utilised.
Applying electric voltage will reverse the effect and crystals are stimulated to change
their structure (expansion, vibration).
4.3 Setting options - appliance with a display
4.3.1 Programme selection
1. Close the door and switch the dishwasher on.
2. Press button B and keep it pressed.
3. Turn control knob C until the chosen setting range is shown in the display.
4. Release button B.
5. Turn control knob C until the chosen setting is shown in the display.
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