Fluke Biomedical 10100AT - Manual (Page 47)

Theory of Operation
Introduction
3
3-1
Section 3
Theory of Operation
3.1 Introduction
The Model 35050AT Dosimeter/kV Readout, when used in conjunction with the Model 35080/80A/80B
kVp Divider and the Model 96035B / 96020C Ion Chambers, forms a complete microcomputer-based
diagnostic radiological test system capable of measuring radiographic exposure, kVp, and exposure time.
This section will describe the basic theory of operation of the Model 35050AT Dosimeter/kVp Readout.
Information pertaining to the theory of operation for the Models 35080/80A/80B kVp Divider may be found
in their respective instruction manuals. This section will begin with the presentation of a simplified
hardware function block diagram accompanied by a description of each block. It will end with a
description of the internal measurement techniques used in conjunction with the electrometer to achieve
offset and drift nulling. Descriptions of the methods for kV peak detection and exposure time
measurements are also included.
As a dosimeter, the Model 35050AT Dosimeter effectively automates all of the error correction and unit
conversion functions that were manually performed by the operator in earlier dosimeters. These
corrections may optionally include those for air density. Exposure and exposure rate measurement
results may be directly displayed in the radiological units of choice, or as electrical charge and current if
preferred. The peak voltage output of the kVp divider may be directly displayed in units of kVp with
corrections for filter pack offset and gain taken into account. The ability to measure exposure time is
based on the use of a threshold set at 75% of the kVp. The Model 35050AT Dosimeter includes an RS-
232 serial communication port that allows complete computer control of the measurement system. The
communications port, in conjunction with an internally located non-volatile memory (EEPROM), also
provides a means of customization and calibration of the Model 35050AT Dosimeter.
3.2 Overall Functional Description
Figure 3-1 represents a simplified hardware function block diagram for the Model 35050AT Dosimeter.
While the most important interblock connections have been shown, many interconnections have been
omitted in order to maintain clarity. Three external connections are illustrated: RS-232 Computer
Interface, Ion Chamber Input Connector, and Model 35080/80A/80B kVp Divider Input Connector.