Removal of the X-ray head requires securing the scissors arm in a semi-
opened position to prevent accidental opening (spring-loaded). Refer to
Figure 3-6. Scissors arm strap.
HELIODENT 70 FUNCTIONING
a. Description of Function. Refer to figure 3-7, the logic block diagram
describing the functioning of the Heliodent 70.
(1) The Heliodent 70 X-ray tube is indirectly heated, i.e., the heater and the
high voltage are switched on at the same time. Thus, tube current flows only once the
emission temperature of the filament is reached (after 150 to 250 msec [millisecond]).
As soon as the peak tube current exceeds a given value, the Schmitt trigger (V6)
switches over, the AR relay energizes, and the timer circuit, consisting of C3/R10, V12,
V14 is triggered. The AR relay shorts the resistor R18 and separates the resistor R20
from the power source. Accordingly, the Heliodent is then operated from the line
(2) As soon as the capacitor C3 is charged to the threshold voltage set on
the Schmitt trigger, the timer circuit shuts the ER relays down, and the exposure is
terminated. The AR relay drops only as the trigger switch is released.