c. Line Input. Fuses U2 and U3 protect the line input. If the switch S1 is on,
the readiness indicating B1 lamp lights. Refer to figure 3-10.
d. Control Transformer. The control transformer ensures that the Heliodent 70
is always operated with a primary voltage of 125v in the line voltage range of 109v to
133v at 60 Hz, 109v to 132v at 50 Hz. The supply of the control transformer is changed
to such an extent with the switch S6 as a function of the input voltage that a voltage of
125v is measured between the terminals T3.1-7. Refer to figure 3-10.
e. Start of Exposure. Refer to figure 3-10.
(1) When you depress the exposure button S27 the relays ER1 and ER2
are controlled via V21 synchronized to the power supply. The Schmitt trigger (V12,
V14) switches and the ER relay energizes.
(2) The relay contacts place the primary winding of the high-voltage
transformer H1 under voltage through the voltage divider R18/R20. At the same time
the buzzer SU and the radiation indicator B2 are caused to operate. They indicate the
duration of the X-ray radiation acoustically and optically.
f. Exposure (Current Path). Refer to figure 3-10.
(1) The base of transistor V19 is supplied with power supply synchronized
positive half waves and a square wave collector output. This output is differentiated by
C8 and R30. The positive peak controls the transistor V20, diode V23. The inverted
peaks are collected at base V21, when exposure button S27 is depressed V21 turns the
timer on. The voltage via dividers R31, R32 controls V20 and V21 as long as S27 is
(2) Since the capacitor C3 is not yet charged, the transistor V12 is blocked.
V14 obtains base current through the resistor R12/R14, and is then switched through.
As a result, the relays ER1 and ER2 energize.
(3) The emitter current of V14 flows through the potentiometer R13 and
causes a voltage drop in it. It is thus possible to adjust the threshold voltage of the
Schmitt trigger consisting of V12/V14, the transistor V12 can be controlled through only
once its base voltage exceeds the value of 0.7v + on 13.