Fluke Biomedical 07-424 - Manual (Page 10)

Nuclear Associates 07-424
Operators Manual
3-2
3.2 Aperture Alignment
Normally the densitometer will operate for a long period of time with little or no maintenance. However, a
periodic check should be made to ensure top performance. The following procedures should be done
yearly.
Check aperture alignment as described in Section 3.1, step 2. If any misalignment is noted, correct it as
described below.
1. Unplug the power cord.
2. Remove the top rear cover by taking out the four (4) screws securing it to the base.
3. Using a 5/32-inch (4 mm) Allen hex wrench, loosen the three (3) screws at the rear of the arm
spring, one complete turn.
DO NOT LOOSEN THE THREE (3) SCREWS ON
THE ARM ITSELF.
4. First inspect the o-ring for damage. If it is, replace it. The push the arm down, with the aperture
removed, until the o-ring is exactly centered in the aperture holder.
5. Tighten the three (3) spring screws, alternately, a quarter turn at a time, until they are fast, while still
holding the arm down.
6. The arm should now be exactly aligned.
3.3 Calibration
A calibrated quality control step tablet, P/N 010128, is supplied with the instrument. To check long-term
precision of the instrument, the step tablet should be used at least monthly according to the directions on
the envelope. A step tablet is furnished with the instrument at the time of shipment. Factory calibration is
performed so that the instrument and the step tablet are simultaneously calibrated. Although this step
tablet is calibrated with high accuracy, its primary use is to check for any drift in the instrument supplied
with the step tablet.
If the instrument is to be calibrated using another standard calibration step tablet such as Eastman Kodak
#3 (Catalog Model No.07-460), the following considerations should be taken into account.
2. Use a 3 mm aperture and plot indicated readings versus readings on the calibration sheet supplied
with the tablet. The slope of this line should be exactly 1.00.
3. Using a small screwdriver, adjust the CAL until the desired calibration is achieved. This can be
done by drawing the best straight line through the plotted points, with the origin at zero and noting
the correction necessary at, for example, a density near 2.50.
4. Put the tablet on a step reading close to 2.50 and adjust the CAL control until the desired correction
has been made, such as increasing the indicated reading +0.02.
The calibration method is necessary due to the inaccuracy inherent in even the best calibrated step
tablets. Eastman Kodak rates the accuracy of their #3 Step Tablet calibration at +0.01 or 3% of indicated
density, whichever is greater. Thus with a perfect densitometer, the errors on a brand new tablet (with no
emulsion flaws or wear), would be as shown in Table 3-1.
NOTE