Planmeca Proline CC, Technical Manual

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Chapter A - GENERAL & TECHNICAL DATA
A-8 Planmeca Proline CC panoramic x-ray
Technical Manual
5.2 Maximum exposure rate
The maximum operating frequency is limited due to the heating of the X-ray tube. There are two
different limiting factors:
First is the time that has to be waited between exposures in order to allow the heat to spread out
from the tube anode into the oil of the tube head. If this was not done, the tube anode can start to
melt during the next exposure.
The second factor is the maximum allowed temperature of the tube head itself. It shall not
exceed 60 °C because of the thermal expansion of the oil and also because of the thermal limits
of the components inside.
In Planmeca Proline CC Panoramic X-ray unit, there is an automatic function implemented in the
microprocessor to calculate the cooling periods between the exposures. Depending on the type
of the X-ray tube and the exposure parameters used the wait time will be calculated and shown
in the clock display. This function protects the X-ray tube not allowing an exposure to be taken
while the wait time is on. The maximal wait time that can be generated by this function is about 1
min. 40 sec., so it does not remarkably reduce the actual exposure rate and still makes it impos-
sible to destroy the X-ray tube by misuse.
In order to control the tube head temperature the microprocessor is measuring it all the time. If it
raises above 40 °C the fan is started and if it raises above 60 °C the temperature is displayed in
the clock display and further exposures are prevented. The system is not able to calculate the
actual waiting time in this case because that depends mainly on the ambient parameters (room
temperature, air flow etc.), but the temperature is displayed to allow the user to estimate the wait-
ing time. (It will normally be about 10 min.) It is very important that the temperature measurement
is in order. Therefore it is checked all the time and an error message is generated, preventing fur-
ther exposures, if the measurement circuit is either short circuiting or an open circuit.