Fluke Biomedical 35080M - Manual (Page 18)

Theory of Operation
Introduction
3
3-1
Section 3
Theory of Operation
3.1 Introduction
When used with the Wide Range Filter Pack (37617) the Model 35080M kVp Divider produces an output
voltage that closely follows the voltage applied to the X-ray tube. It does this with a 10-90% response
time of 150 microseconds, so the waveform can be used not only for determining kVp, but also for making
precise time determinations and for diagnosing generator malfunctions.
3.2 Measurement Theory
In this measurement scheme, two X-ray detectors are used (refer to Figures 3-1 and 3-2). The X-ray
beam passes through a relatively heavy filter prior to striking detector A, and through a lighter filter prior to
striking detector B. The ratio of the currents (I/I) is transformed to a voltage by a custom-designed ratio
module.
Typically, this ratio voltage increases as the voltage applied to the X-ray tube increases. The ratio
voltage is virtually independent of the current applied to the X-ray tube and the distance to the X-ray tube.
3.3 Wide Range Filter Pack (37617)
The Wide Range Filter Pack (37617) is a standard filter pack supplied with the Model 35080M kVp
Divider. This filter pack gives linear performance over a wide 50-150 kVp range. Detailed characteristics
of the filter pack are given in Section 1, General Information, and Section 2, Operating Instructions, of this
instruction manual.
Figure 3-1. Simplified Functional Block Diagram of the Model 35080M kVp Divider