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

Models: 35040

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

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

2-1

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

Contents

Therapy Dosimeter 35040Fluke Biomedical Table of Contents Troubleshooting and Service Addendum Features of Firmware Version 27JAN00 or LaterSample Customization Reports Iii Blank Features IntroductionIntroduction Before You Start Safety Precautions Safety Symbols And TermsOperators Manual Manual Addenda SpecificationsFactory Calibration Error Source ± %rdg Maximum ErrorCurrent Measurements Full Scale Range Display Resolution Noise ± countsFull Scale Range Display Resolution Timed Charge MeasurementsSpecifications Effective Exposure Time MeasurementsGeneral Measurements High Performance Power Supply and Battery Charger Unpacking and Inspection 35040 Functional Description Hardware Block Diagram of the Model 35040 Therapy DosimeterSerial Communications Port Power SupplyFront Panel MicroControllerMultiplexer and A/D Converter Basic Operating EquationsElectrometer Bias SupplyQAccumprevious Quantity Description Units CommentsQExposure QAccumCharge and Current Measurements Leakage Measurements= time of electrometer conversion s Timed Charge and Dose Exposure Charge and DoseExposure Current and Rate Setting ThresholdsPredicted Timed Charge and Dose Accumulated Charge and DoseDoseRate = I a × Iccf Units/C × Adcf × RateMultiplier s Exposure TimeAir Density Correction Factor ⎝ PMm Hg = inch Hg x Units Display Minimum Maximum Standard Resolution ErrorIntroduction SetupSetup Front Panel FamiliarizationRear Panel Familiarization Powering The SystemIon Chamber Connector Power-Up Self-Test and Display MessagesBasic Measurement Techniques General ConsiderationsMaking Non-Timed Exposure Measurements Timer Setup Timer Use3Making Timed Exposure Measurements Using Other Ion Chambers Battery CareFront Panel Controls PowerBattery Care Operation InstructionsPowering Up the Model 35040 Therapy Dosimeter Powering Down the Model 35040 Therapy Dosimeter Using the Test Function ButtonOperation Instructions QScaleFactor=1.0000 IScaleFactor=1.0000 5Automatic Leakage Compensation 12. The Test Function Screen Showing the Timer SettingsCalibrated by Keithley RMD Nov 15 17. The Test Function Screen Showing the Timer Settings 6Timer SetupUsing the AIR Density Button Using the Detector Select ButtonUsing the Bias Select Button Using the Units Select ButtonSet 300.0 V 100% Central Electrde Pos IC Bias 300.0 V CEP Overranging Conditions Using the RESET/MEASURE ButtonReset Error Overrange ConditionsCondition Values Overranged Annunciator Condition Reset Error With Automatic Leakage Compensation EnabledAnnunciators AnnunciatorsCondition Overranged Measurement Measurement Indicators and ConditionsIndicator Measurement Condition ? left of valueStarting the Customization Software Installing/Uninstalling Customization SoftwareCustomization Connection to the ComputerDownloading Menu Items and ControlsCOM Port Drop Down List Ion Chambers Close or File CloseFile Save AS and File Print Edit Special Items OK and Cancel36. The Special Items Menu Calibration Temperature has focus Download and CancelMeasurement Displays Display Line Operators Manual Available Display LinesChanging a Line on a Display Using the APPEND, DELETE, and Insert ButtonsDisplay Line Group Selection Selecting an Item and Placing It38. The Timer Intervals Form Timer Intervals39. The Bias Settings Form Bias SettingsExamples Deleting a Display Changing the Pressure UnitsCustomizing a Measurement Display Appending a DisplayErrors Troubleshooting Troubleshooting and ServiceSymptom LoBias annunciator displayed Symptom Display does not light up when Power is pressedSymptom ??Bias annunciator displayed Symptom HiBias annunciator displayedDo not make Symptom Internal Reset Error displayedSymptom Configuration Error displayed Bit Description ActionMeasurements. Return Symptom Current Overrange DisplayedSymptom Dashes displayed instead of digits Symptom Bias voltage measurement changes by one digitExample 299.9 to Display Will Not Light Hours? Is the battery voltage greater than 5.9 volts? Low BatteryBias Error Go toLine Model 35040 Therapy Dosimeter Fuse Replacement Line Fuse ReplacementInterface Connector Cleaning Cleaning The InstrumentReplaceable Parts Information Replaceable Parts Information Warranty InformationReplaceable Parts List Recalibration, Repair Information & Technical AssistanceBlank Sample Documents Sample Customization Reports35040 Appendix Sample Customization Reports 35040 Appendix Sample Customization Reports Blank Introduction New Features OverviewTimed Measurements Specifications Update New Features B SetupTimer Setup Procedure Timer Use ProcedureMaking Timed Exposure Measurements Setup B RESET/MEASUREAutomatic Leakage Compensation ADC ALCOperation Instructions B Start NA pA Stop Thres CurrentDecimal Places Timer SetupAnnunciators, Indicators, and Overrange Conditions Table B-2. Measurement Indicators and ConditionsTable B-1. Annunciators Condition Overranged Measurement1 Table B-3. Overrange ConditionsTheory of Operation Theory Of OperationConfiguration Error Service Required Error Number Main Menu Measurement MenuMeasurement Displays Figure B-9 shows the Measurement Displays dialog box Table B-4. Available Display Lines Figure B-10. The Timer Intervals dialog box Page Fluke Biomedical