Fluke Biomedical 07-440 - Manual (Page 13)

Maintenance & Calibration
Calibration
3
3-3
2. 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 correct reading is
shown.
The calibration method is necessary due to the inaccuracy inherent in even the best calibrated step
tablets. Assuming a Step Tablet calibration accuracy of to ± 0.01 (or 3% of indicated density) and a
perfect densitometer, the errors on a brand new tablet (with no emulsion flaws or wear) would be as
shown in Table 3-1.
While the accuracy should be checked once a year, in most cases no CAL adjustment will be necessary.
For quality control purposes, the calibration of the instrument with a film tablet is quite sufficient. However,
it should be noted that the slope of the indicated density curve will change if any color shifts are caused
by the materials being measured. Although the light source is close to the ANSI standard of typical
response of the human eye, it is not exact. Therefore, films which produce a spectral shift may produce
consistently higher or lower density readings. In such cases, a calibrated step wedge of the same material
as is being measured is necessary to adjust instrument calibration.
3.4 Lamp Replacement
Disconnect the unit from the power supply before
removing cover or changing fuses.
3.4.1 Table Lamps
The four (4) #37 lamps which provide table illumination have a life expectancy of approximately 1500
hours. #74 lamps can be used in their place to provide greater brilliancy, but average life is only about
500 hours. Use the following procedure to replace the lamps:
1. Remove the two (2) screws holding the plastic table to the case.
2. Carefully lift out the table using the finger slots provided on either side.
3. The lamps will be clearly visible and, being of the wedge base type, can be removed by pulling up
on them.
4. Insert the four (4) #37 replacement lamps provided in the spare parts kit supplied at the time of
shipment.
When inserting new lamps, make sure that the wire
contacts are in proper position, otherwise good
contact will not be made.
WARNING
NOTE