Siemens MOBILETT Plus Manual page 51

Tube-loading calculation
The block diagrams and the wiring diagram X037E, sheet 140 are the basis for the func-
tional description given below.
The tube-loading calculation is performed by the 80C535 microprocessor on CPU board
D1.
It fulfills two tasks:
1.
2.
This makes use of a so-called HU memory, in which the heat units calculated from the kV
and mAs values used in each exposure are summed.
The memory contents are continuously compared with a HU limiting value of about 80%
of the permissible thermal loading in HU.
100%
80%
67%
Fig. 1
Between exposures, the contents of the HU memory are reduced by 13 Joules every 250
ms in order to simulate the cool-down characteristic of the X-ray tube assembly. 13 Joules
represent about 52 W cooling capacity.
Siemens-Elema AB
Solna, Sweden
it prevents the thermal loading of the anode plate from exceeding a maximum of
80 % of the permissible loading (in HU = Heat Units) and
it limits the long-term (one hour) mean value of the X-ray tube heat reduction to
73 W.
Last
exposure
Calculated anode plate
heat energy
Register 6
"Ready" off
"Ready" on
Calculated cool-down of
anode plate heat energy
SPR8-215.850.02
Rev. 01 01.02
17
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