Dräger Savina 300, Technical Documentation Manual, Page: 19 / 166

Savina 300
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Function descriptions
Control panel with TFT colour display
Touch-panel
Analog-resistive touch-screen
Fig. 8 Analog-resistive touch-screen
Analog systems consist of two opposing conductive indium tin oxide (ITO)
layers (x and y layer) which are actuated with a constant direct voltage.
Indium tin oxide is a transparent semiconducting material.
Between the two ITO layers there are a large number of small, barely visible
so-called spacer dots which ensure the two layers are kept separate.
In 8-wire systems the touch-screen has eight wires routed to the controller –
four for each axis.
When the touch-screen is touched at a certain point where the two ITO layers
are located an electrical contact is produced. The resistance of this contact
results in a different voltage at each point. The change in voltage is then used
to define the x and y coordinates.
The Central Control Board controls the communication between the proces-
sor system and the touch-screen. The correct position is determined with the
aid of the relevant software drivers. The analog touch-screen works very pre-
cisely, and provides a high resolution.