Fluke Biomedical 35080B - Manual (Page 19)

Theory of Operation
Output
3
3-3
3.4 Output
In the Model 35080B kVp Divider, the intensity ratio is taken with a high-speed logarithmic ratio module.
Thus, the output of the Model 35080B kVp Divider follows the kVp waveform applied to the x-ray tube
within the linear range of the filter pack. The waveform differs from the waveform output of a resistive
divider in that information below the kV baseline of the filter is not displayed (see Figure 3-3).
3.5 Intensity Cutoff
An examination of the Model 35080B kVp Divider waveforms in Figure 3-3 shows that as the potential of
the x-ray beam waveform increases for the first time, the Model 35080B kVp Divider follows the signal as
soon as it comes into the linear range of the filter pack. However, as the x-ray signal decays, the signal
presented to the oscilloscope will suddenly switch to the filter pack’s baseline. This effect is caused by a
special circuit that prevents the presentation of a distorted signal to the oscilloscope. This circuit
automatically resets about 10 seconds after an exposure is made.
3.6 Internal Calibration
In order to assure that the ratio circuit in the Model 35080B kVp Divider is stable, a “CAL” position is
provided on the function switch. When the Model 35080B kVp Divider is switched into the “CAL” position,
a signal ratio of 0.25 is electronically switched into the ratio circuit. This produces an output of 0.75 volts
with no filter pack inserted. This value should be within ± 1% of 0.75 volts. When the Wide Range Filter
Pack (37617) is inserted, a CAL voltage of 0.40 volts ± 1% is produced at the Model 35080B kVp Divider
output. The CAL voltage is inscribed on each of the other filter packs. The value in kV is also given and
this may be used to check the oscilloscope calibration.
If the Model 35080B kVp Divider is exposed to an
x-ray beam while the function switch is left in the
“CAL” position, the resulting scope presentation will
be badly distorted.
NOTE