Fluke Biomedical 07-451 - Manual (Page 5)

General Information
Introduction
1
1-1
Section 1
General Information
1.1 Introduction
The X-Ray Output Detector offers a unique means of calibrating and trouble-shooting both diagnostic and
therapeutic x-ray generators. When used with a storage or camera oscilloscope, the system displays the
intensity-time relationship of an x-ray beam. The detector is simply placed in the x-ray beam, and the
output cable is connected to the oscilloscope input. The resulting wave-shape patterns may be utilized to
calibrate and/or diagnose malfunctions in the x-ray generator.
The detector supplies a 100-200 mV peak signal at standard diagnostic conditions (80 kVp, 100 mA).
This high output permits the simple interpretation of oscilloscope displays. Since the detector has a rise
time of about 1 μ/sec, no alternation of the true x-ray output pulse shape is introduced. This solid-state
detector requires no power input.
1.2 Theory
The detector utilizes silicon diodes that have very high sensitive volume and very low mass
encapsulation. The characteristics of diode detectors, when used with x-rays, are similar to that of a
silicon diode detector when used for light. When such a detector is used as a current generator with very
low input impedance to the measurement device, the output is linear with the input x-ray intensity.
However, if the detector is operated into a very high impedance such as an oscilloscope, which is
commonly 10 megohms, the output will be logarithmic. When operated in this voltage mode, the actual
detector rise time as measured on the oscilloscope will depend on the cable capacity. As short a cable as
possible should be used with as low a capacity as possible. It is suggested that RG-58u cable be used.
When the unit is used with an oscilloscope, the output is logarithmically compressed. The interpretation
of this trace, nevertheless, is not altered for such difficulties as contactor problems, timer calibration,
loading, arcing or rectifier malfunction, all of which are interpreted in the same way as with a linear output.
The Model 07-451 is connected so that it will produce a negative voltage output by negative current on
the center conductor of the cable.