STEP 2 : Dose verication (mGy)
The dose in air is measured with a “non invasive” instrument, by positioning the detector at a source-skin distance
= 31cm (12”) (SSD) or 20cm (8”) (SSD)
SET TECHNICAL FACTORS
NOMINAL VOLTAGE Vn ± 10%
MAXIMUM VOLTAGE DROP 3%
NOMINAL HIGH VOLTAGE 70 kV
NOMINAL CURRENT 8 mA
SET EXPOSURE TIME 1 s
Dose in air is:
SOURCE-SKIN DISTANCE
31 cm = 12”: 70 kV – 8 mA = 5,5 mGy/s ± 30%
20 cm = 8”: 70 kV – 8 mA = 12 mGy/s ± 30%
STEP 3 : Checking the exposure time (s)
The exposure time is measured with a “non invasive” instruments.
SET TECHNICAL FACTORS
NOMINAL VOLTAGE Vn ± 10%
MAXIMUM VOLTAGE DROP 3%
NOMINAL HIGH VOLTAGE 70 kV
NOMINAL CURRENT 8 mA
SET EXPOSURE TIME 3,2 s
The exposure time measured is 0,2s ±5% or ±20ms, whichever is larger.
PLEASE NOTE
The “x-mind ac®” timer features the «selfcompensating» technology.
The automatic correction works as follows:
- a voltmeter located inside the timer constantly reads the mains voltage, while the operator selects the required exposure time;
- the last measure collected before the exposure is sent to the internal microprocessor, that corrects the exposure time set by the operator by
applying a special algorithm;
- at the end of the exposure, during the pause time (approx 32 times the set time), the time corrected value is shown on the display of the
timer.
THE CORRECT TIME IS THE ACTUAL DURATION OF THE EXPOSURE
While performing periodic quality checks, some differences between the set exposure time and the measured exposure time may be detec-
ted.
The exposure time is accurate when:
AS REGARDS TO THE SET TIME
►
MAXIMUM ERROR IS ±100% WHEN LINE VOLTAGE IS ±10% OF THE NOMINAL VOLTAGE
►
MAXIMUM ERROR IS ±10% or ±20ms WHEN LINE VOLTAGE IS EQUAL TO NOMINAL VOLTAGE
AS REGARDS TO THE TIME SHOWN ON DISPLAY
►
MAXIMUM ERROR IS ±10% or ±20ms WHEN LINE VOLTAGE IS EQUAL TO NOMINAL VOLTAGE
PERFORM THE CHECK OF ACCURACY OF THE EXPOSURE TIME AS DESCRIBED IN THE FOLLOWING INSTRUCTIONS.
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