Fluke Biomedical 35080M - Manual (Page 56)

Appendix
Correcting kVp Measurements For Gain Effects
B
B-1
Section B
Correcting kVp Measurements for Gain Effects
B.1 Introduction
The purpose of this addendum is to provide an
alternative method for users with sealed units,
who cannot access the adjustment
potentiometers.
The calibration mode feature of the Model 35080M kVp Divider provides a method to monitor the gain of
the internal circuitry. When the kVp divider is placed in CAL mode, the specific voltage and kVp stated on
each individual filter pack should be obtained. If the output voltage in CAL mode is not within ± 1% of the
value stated on the pack, kVp measurements should be corrected in one of the following ways,
depending on the device used for measuring the output of the kVp divider. A deviation of less than ± 1%
will result in a maximum kVp error of 0.75% of reading.
B.2 Oscilloscope Measurements
The Model 35080M kVp Divider Instruction Manual describes the technique that should be used to
measure kVp when connected to an oscilloscope (refer to Section 2.4). A slight modification of this
technique will allow for the correction of gain effects. Briefly, this technique is as follows.
1. Insert the filter pack to be used into the kVp divider and connect to the oscilloscope. Set the
oscilloscope gain to an appropriate value depending on the sensitivity of the filter pack.
2. Set the oscilloscope coupling to GND and adjust the vertical position such that the trace coincides
with the bottom horizontal line on the screen. This line now corresponds to the Zero offset kVp
given on the pack.
3. Set the oscilloscope coupling to DC and switch the kVp divider to the CAL position. The
oscilloscope trace should now be at a level corresponding to the CAL kVp given on the filter pack.
If this is not the case, the gain effects should be corrected before making kVp measurements in the
RUN position.
4. The gain effects can be corrected by adjusting the fine-tuning knob on the Volts/div switch of the
oscilloscope. While still in the CAL position, adjust this knob until the trace on the screen
corresponds to the kVp value expected for the filter pack in use. Measurements made in RUN
mode will now be corrected for gain effects.
NOTE