g. Switching Relay AR. Refer to figure 3-10.
(1) As soon as the tube current allows a voltage drop on the resistor R3
which is greater than the following.
U (V4) = 2.4v + U (V5) = 0.7v + U (V6) = 0.7v, the transistor V6 is controlled through.
Then, the transistor V7 is also controlled through R9. The collector current of V7 allows
the AR relay to draw. This relay places the Heliodent 70 transformer under a voltage of
125 without damping.
(2) The collector current of V7 flows, at the same time through V8, R8, R5 to
the base of V6, and keeps V6 in the over-modulated state (flip-flop function). The
(3) The transistor V7 also controls the transistor V17. This transistor serves
as an impedance converter and provides a supply voltage stabilized by V18 to the
integrator, consisting of R10 and C3. The exposure times of 0.066 and 3.2 seconds
(sec) are set in 18 steps with R10.
h. End of Exposure. As soon as C3 is charged to the threshold voltage, which
is adjusted with R13, the transistor V12 switches through. This initiates a flip-flop
process. On the one hand, the transistor V12 short circuits the base section of V14, so
that the current through ER is reduced. On the other hand, the voltage drop on R13
decreases so that the transistor V12 is controlled through even faster. Thus, the ER
relays drop. Refer to figure 3-10.
i. Temperature Compensation. The R11 hot wire compensates the
temperature response of the entire circuit in the 10 to 70 Celsius (C) range. Refer to
j. Forced Exposure. Refer to figure 3-10.
(1) In case of a defect where no tube current signal triggers the Dentotime,
there is a forced switching system. The capacitor C7 is charged through the resistor
R16 after switching on.
(2) If no tube current pulse triggers the Dentotime, the transistor V6 is
controlled through over R16 after approximately 0.7 to 1 sec and the timer circuit is