LORAD AFFINITY Series, Service Manual

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P/N 9-500-0255 4-37
Service Manual
Chapter 4: Calibrations and Performance Checks
Performance Checks
1. On the IRSD, place 6.0 cm of acrylic attenuation on an empty cassette. Position a radia-
tion probe (10 square cm) on top of the phantom.
2. Align the probe position with the AEC sensor at front center on the IRSD. Use the light
field and collimate the x-ray field to the approximate size of the probe.
3. Set the unit for an Auto-Filter exposure using the Large focal spot. Make 10 exposures
and record the milliroentgen readings for each exposure.
4. Calculate the average milliroentgen reading. Subtract each actual reading from the aver-
age. Square each difference. Add the squares and divide their sum by 9. Take the square
root of the result.
5. Divide the number obtained in Step 3 by the average milliroentgen reading. The quo-
tient, called the coefficient of variation, must be less than 0.05.
Note … To calculate the coefficient of variation, use the Reproducibility Worksheet
(Table 4-14) which sequences the steps to calculate the quotient. Table 4-14
also provides a formula to calculate the quotient using a statistical
calculator. Note that the kV and mAs values are not set for this check.