LORAD AFFINITY Series, Руководство по обслуживанию

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4-36 P/N 9-500-0255
Service Manual
Chapter 4: Calibrations and Performance Checks
Performance Checks
13. Divide each Step 11 difference value by each Step 12 sum value. If the result for any pair
exceeds 0.10, the test is considered failed.
14. Repeat Steps 8 through 13 using the Small Focal Spot.
15. If the unit fails any part of the above test, first recheck all calculations, then repeat the
tests. Failure to meet these performance standards indicates the need to check the x-ray
tube’s kV, mA, and mR outputs.
6.3 Reproducibility in Auto-Time Mode
The following test verifies that the automatic exposure control system is operating
consistently in the Auto-time exposure mode. Record the readings and mathematical
calculations in the Reproducibility Worksheet (Table 4-14).
1. On the IRSD, place 4.0 cm of acrylic attenuation on an empty cassette. Position a 10-
square cm radiation probe on top of the acrylic.
2. Center the probe position directly above the AEC sensor. Use the light field lamp to visu-
alize the x-ray field and collimate appropriately so that just the probe is exposed.
3. Set the unit for an Auto-time exposure at 25 kV, Mo Filter, Large Focal Spot. Conduct ten
exposures. Record the milliroentgen and post-exposure mAs readings for each exposure.
4. Calculate the average mR reading and subtract each actual reading from the average.
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 4 by the average milliroentgen reading. The quotient
- or coefficient of variation - must be less than 0.05.
6. If the coefficient of variation greater than 0.05, check the calibration of the Automatic
Exposure Control System.
6.4 Reproducibility in Auto-kV Mode
The following test verifies that the automatic exposure control system is operating
consistently in the Auto-kV exposure mode. Record the readings and mathematical
calculations in the Reproducibility Worksheet (Table 4-14).
1. Set up the mammography system and radiation probe exactly as in Step 1 of the Auto-
Time Reproducibility Check (Section 6.3).
2. Set the unit for an Auto-kV exposure, using the Mo Filter and the Large Focal Spot. Con-
duct ten exposures. Record the milliroentgen and post-exposure mAs readings for each
exposure.
3. Calculate the average mR reading and subtract each actual reading from the average.
Square each difference. Add the squares and divide their sum by 9. Take the square root
of the result.
4. Divide the number obtained in Step 3 by the average milliroentgen reading. The quotient
(called the coefficient of variation) must be less than 0.05.
5. If the coefficient of variation is greater than 0.05, check the calibration of the Automatic
Exposure Control System.
6.5 Reproducibility in Auto-Filter Mode
The following test verifies that the automatic exposure control system is reproducible in the
Auto-Filter exposure mode. Failure to meet this performance test indicates the need to check
the calibration of the Automatic Exposure Control System.