Fluke Functional Description, Hardware Block Diagram of the Model 35040 Therapy Dosimeter

Theory of Operation

Introduction 2

Section 2

Theory of Operation

2.1 Introduction

The Model 35040 Therapy Dosimeter is a radiation measurement instrument intended for use in calibration procedures for high-energy accelerators, 60Co, and brachytherapy. Basic theory of operation of the instrument is explained in the following paragraphs. For information on radiation dosimetry and ion chamber measurement theory, the reader should refer to one of the standard radiological physics texts.

2.2 Functional Description

The Model 35040 Therapy Dosimeter is a portable instrument that measures charge and current. Calibrated ion chamber factors convert charge and current to directly measure radiation dose and dose rate in the user specified radiological units. The reading may be corrected for air density by the user entering ambient temperature and barometric pressure readings. The electronic bias setting is selectable from the front panel.

AC Line	FUSE
BATTERY
PACK	POWER	POWER
		SWITCH
			FRONT PANEL	VFD
	SUPPLY	CONTACTS
			SWITCHES
				DISPLAY
	POWER	BATTERY	SELECTION
			SWITCH
	CONTROL	STATUS
			CONTACTS
					RS-232
				SERIAL	COMPUTER
		PROCESSOR		COMM.	INTERFACE
					CONNECTION
				PORT
				HIGH VOLTAGE ISOLATION
		BIAS CONTROL
	ELECTRONIC
	BIAS SUPPLY		CONVERSION	CONVERSION
			CONTROL	RESULTS
	BIAS
ION
CHAMBER
	ELECTROMETER		MULTIPLEXER AND
CONNECTOR
			A/D CONVERTER

Figure 2-1.Hardware Block Diagram of the Model 35040 Therapy Dosimeter

2-1