Planmeca Proline XC Technical Manual page 205

PREVENTIVE MAINTENANCE CHECKS
Exposure time measurement
2.2.2 INVASIVE TESTING (directly from the units own feedback signals)
NOTE
Peak tube potential (kVp) measurement
Tube current (mA) measurement
Technical Manual
The exposure time is controlled by the microprocessor, so the exposure time accuracy is
exactly the same, no matter if the set exposure time is 200 ms (in film cephalostatic mode) or
16 s (in panoramic / tomographic mode). The exposure time is defined automatically based
on the selected program and is displayed in the upper right corner of the graphical user inter-
face. In panoramic mode, attach the non-invasive sensor to the front panel of the cassette
holder (or Dimax3 sensor) and make sure its whole area is in the radiation field. Select 70 kV
/ 8mA and press ready. Take an exposure and record the measured exposure time. The
measured exposure time must be within ±10% of the exposure time displayed in the user
interface.
In film cephalostatic mode, the exposure time is selected by the user. Select the shortest pos-
sible exposure time, attach the non-invasive sensor to the cephalostatic cassette holder in the
middle of the radiation field, take an exposure and record the measured exposure time. When
placing the sensor, note that if the unit is equipped with auto-ceph, the cassette size is auto-
matically detected when the cassette is on its place and the area of radiation field is adjusted
accordingly.
The manufacturer does not require the invasive testing. The invasive test must only be
performed if the local authorities require it.
An invasive method should be used for checking the tube current (mA), and can be used for
checking the kVp and exposure time. This method requires that the covers around the tube
head assembly are removed. The analog feedback voltage signals can be measured with a
calibrated multimeter. An oscilloscope is required if kV and mA waveforms need to be
observed, for an example when determining the exposure time.
Select the voltage mode of the multimeter. Connect the positive plug of the multimeter to the
Generator CPU board's connector P18:10 KVM-signal. Connect the negative plug of the mul-
timeter to the Generator CPU board's connector P4:2 (GND). Select the appropriate DC volt-
age measurement range for 1 to 5 V signal level. Take an exposure with desired kV setting
(selected mA value has no effect, however low mA should be used to minimise the amount of
unnecessary radiation) and when the voltage reading has stabilized, record it. The actual tube
voltage relates to the measured feedback signal as follows:
Actual tube voltage = 17 467 * measured feedback voltage (in volts)
The resulting tube voltage should be within ±5% of the voltage indicated in the user interface.
Select the voltage mode of the multimeter. Connect the positive plug of the multimeter to the
Generator CPU board's connector P18:11 MAM-signal. Connect the negative plug of the mul-
timeter to the Generator CPU board's connector P4:2 (GND). Select the appropriate DC volt-
age measurement range for 100mV to 5 V signal levels. Take an exposure with desired mA
setting (selected kV value has no effect, but lowest possible kV is recommended to minimise
the amount of unnecessary radiation) and when the voltage reading has stabilized, record it.
The actual tube current relates to the measured feedback signal as follows:
Actual tube current (in mA) = 2.61 * measured feedback voltage (in volts)
The resulting tube current should be within ±10% of the current indicated in the user interface.
Chapter F - PREVENTIVE MAINTENANCE
Planmeca Proline XC X-ray unit F-5