GE AMX-II

GENERAL ELECTRIC MEDICAL SYSTEMS АМХ-П Х-ААУ ИМТ
6-978 SM A 0654E
SEC. 8 EXPOSURE TERMINATION
There are several means for terminating an exposure. These are individually described below.
81 Radiographic Timer Termination by Forced Commutation
Schematic reference sheet 4 4 9, Chapter 7.
After the rotor button is depressed 1C2 (38,E) is charged to a -80 volts as shown in Illustration 6-14. 1C1
does not charge due to 1CR2.
1CR2 1CR1
| 3R5
1C1
162 POWER TO
CHARGE 1С1
373 TO 50 HZ
SEC. 4 INVERTER
18796-D10
ILLUSTRATION 6-14
During an exposure 2CR2 (38,D) is conducting and 2CR1 is off. When the exposure is to be terminated,
a signal is applied to the gate of 2CR1 (39,D) turning it on, illustration 6-15. Capacitor 1C2 will discharge
through 1C1, 2CR2 and 2CR1. This forces more current through 2CR2 in the reverse direction than was
flowing in the forward, shutting it off. The reverse current charges 1C1 until 2CR2 shuts off.
The Timer consists of an RC timing circuit and UJT 2A1017 (86-87,D) which is turned on at a time period
of mas/100.
At-the end of the selected time period the UJT conducts producing a signal through pulse transforme
3A1T18 (89,E) and 3A1CR44 to turn on 3A1CR47 (88,D). The turning on of 3A1CR47 providesa |
discharge path for 3A1C38 (87,E) through 3A1CR39 (87,C), 3A1CR47, 3A1CR68 and 3A6T5. The
pulse generated by the discharge of 3A1C38 is coupled by 3A6T5 to the gate of 2CR1 (39,D). When
2CR1 conducts, it applies the full negative voltage (-80 v) of 1C2 to the anode of 2CR2 turning it off as
described earlier.
6-18