Service Instructions
Multimobil 5C
Siemens Ltd. Med India
Version 5.0
Page 26 of 73
Copyright
©
SIEMENS LTD. All rights reserved. For internal use only
¾
The mAs values should be within
±
5% for values > 20 mAs and
±
10 % for mAs
≤
20 mAs.
¾
If the values are not within the above range, tune P1 on D915 to adjust the mAs
values.
5.4 Automatic Dosage Regulation
Automatic dose regulation constantly adapts the X-ray radiation to the thickness and
density of the irradiated object in an optimum manner. Through the fast detection of
dose rate, an optimum picture Quality is obtained for a thick object with a minimum
fluoroscopy time. ADR is possible in two different mode of operation 1) Anti-isowatt
and 2) Contrast mode. Fluoroscopy mode is selectable from the control panel (By
default Anti-isowatt mode is selected).
When contrast mode is selected the mA for that particular is increased hence the
contrast of the image when compared to anti-isowatt mode. Check for the same.
The detection circle of the ABC signal is 1/3
rd
the diameter size of the circle blanking
with same centre as that of the image. The pixel shades over the entire circle are
averaged to generate a signal proportional to the brightness / contrast level. This ABC
signal varies from –8V corresponding to total darkness and +8.0 V DC, to bright
image.
This signal is sent to PCB D508, which generates a proportional signal to be applied
as the Automatic Dose Regulation (ADR) signal to the analog port of microcontroller in
PCB D915. The circuit on the PCB D508 consists of level shifter followed by unity gain
buffer in inverting mode-using TLO82. The output of this circuit is a signal proportional
to the darkness / brightness level. The magnitude varies from 0 to 5V DC.
To Adjust the PCB, the following potentiometers are to be tuned
Remove all cable connections coming to the PCB D 508.
Remove IC J15: TL 082, which is mounted on the socket.
Connect a Multimeter between test point ABC and J15 socket pin 2.
Adjust resistance: 126K using VR5
Resistance between test point 0VA and J15 socket pin 6
Adjust resistance: 48.33K using VR2
Resistance between test point J15 socket pin 6 and pin7
Adjust resistance: 49.65 K using VR1.
5.4.1 ADR Stop Mode (Manual)
In ADR Stop Mode, adjustment of kV and mA is possible Manually. In cases where
small adjustments of contrast is required to view the finer details of the image, the kV
and mA values can be adjusted by pressing the ADR stop switch.
When a metallic object comes in the X-ray path (e.g. a marker) or when the deviation
in object density is large (e.g. Repositioning a fracture), it may be required to fix the kV
Values earlier regulated in the automatic mode. Selection of Contrast mode is not
possible in the ADR stop mode.