Fluke 35040 manual Exposure Time, DoseRate = I a × Iccf Units/C × Adcf × RateMultiplier s

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35040

Operators Manual

or dielectric absorption. The start and stop thresholds are set independently, but the stop threshold must be less than the start threshold. The thresholds are settable in 0.1 pA increments from 0.0 pA to 9.9 pA. In some test setups, it may be necessary to raise the thresholds to reliably detect an exposure in the presence of a relatively large leakage current. Since the start threshold determines the minimum dose rate, it may be necessary to lower the thresholds for some exposures.

DoseRate = I [A] × ICCF [Units/C] × ADCF × RateMultiplier [s]

The minimum dose rate is

where I[A] is the start threshold setting.

When the start and stop thresholds are set to 0.0 pA, the automatic detection of start and end of exposure is disabled. This effectively means that the instrument is measuring as if an exposure has been running continuously. In this mode of operation, leakage current is not measured, the average current is measured from the last time RESET/MEASURE was pressed, and charge will accumulate due to leakage current.

NOTE

Thresholds other than those used by the calibration agency may render inaccurate measurements.

2.3.2 Exposure Time

Historically, the determination of exposure time for 60Co has involved multiple exposures to eliminate the effect of the shutter speed. By using the total charge and the average current for the exposure, the effective exposure time can be determined using a single exposure. If the average current varies by more than 10% during the exposure, this measurement is considered invalid and will be replaced by “INVALID.”

	⎛	Q2 [C] − Q1 [C]	⎞	⎛	Q [C]	⎞
	IAvg = ⎜		⎟

	⎜	T 2 [s] − T1[s]	⎟	Time = ⎜		⎟

	⎝		⎠	⎝⎜ IAvg [A] ⎠⎟

The effective exposure time is derived from the total charge and the average current. In order to get enough data points to accurately calculate the time, the exposure must be a minimum of 3 seconds. To avoid artifacts at the start and end of exposure, the average current is calculated over the interval starting 1 1/3 seconds after the start is detected to 1 1/3 seconds before the end of exposure.

2-8

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Contents 35040 Therapy DosimeterFluke Biomedical Table of Contents Addendum Features of Firmware Version 27JAN00 or Later Troubleshooting and ServiceSample Customization Reports Iii Blank Introduction FeaturesIntroduction Safety Symbols And Terms Before You Start Safety PrecautionsOperators Manual Maximum Error SpecificationsFactory Calibration Error Source ± %rdg Manual AddendaTimed Charge Measurements Full Scale Range Display Resolution Noise ± countsFull Scale Range Display Resolution Current MeasurementsEffective Exposure Time Measurements SpecificationsGeneral Measurements High Performance Power Supply and Battery Charger Unpacking and Inspection 35040 Hardware Block Diagram of the Model 35040 Therapy Dosimeter Functional DescriptionMicroController Power SupplyFront Panel Serial Communications PortBias Supply Basic Operating EquationsElectrometer Multiplexer and A/D ConverterQAccum Quantity Description Units CommentsQExposure QAccumpreviousLeakage Measurements Charge and Current Measurements= time of electrometer conversion s Exposure Charge and Dose Timed Charge and DoseAccumulated Charge and Dose Setting ThresholdsPredicted Timed Charge and Dose Exposure Current and RateExposure Time DoseRate = I a × Iccf Units/C × Adcf × RateMultiplier s⎝ P Air Density Correction FactorMm Hg = inch Hg x Standard Resolution Error Units Display Minimum MaximumFront Panel Familiarization SetupSetup IntroductionPowering The System Rear Panel FamiliarizationPower-Up Self-Test and Display Messages Ion Chamber ConnectorGeneral Considerations Basic Measurement TechniquesMaking Non-Timed Exposure Measurements Timer Use Timer Setup3Making Timed Exposure Measurements Battery Care Using Other Ion ChambersOperation Instructions PowerBattery Care Front Panel ControlsPowering Up the Model 35040 Therapy Dosimeter Using the Test Function Button Powering Down the Model 35040 Therapy DosimeterOperation Instructions QScaleFactor=1.0000 IScaleFactor=1.0000 12. The Test Function Screen Showing the Timer Settings 5Automatic Leakage CompensationCalibrated by Keithley RMD Nov 15 6Timer Setup 17. The Test Function Screen Showing the Timer SettingsUsing the Detector Select Button Using the AIR Density ButtonUsing the Units Select Button Using the Bias Select ButtonSet 300.0 V 100% Central Electrde Pos IC Bias 300.0 V CEP Using the RESET/MEASURE Button Overranging ConditionsOverrange Conditions Reset ErrorCondition Values Overranged Annunciators Reset Error With Automatic Leakage Compensation EnabledAnnunciators Annunciator Condition? left of value Measurement Indicators and ConditionsIndicator Measurement Condition Condition Overranged MeasurementConnection to the Computer Installing/Uninstalling Customization SoftwareCustomization Starting the Customization SoftwareMenu Items and Controls DownloadingCOM Port Drop Down List Close or File Close Ion ChambersFile Save AS and File Print Edit OK and Cancel Special ItemsDownload and Cancel 36. The Special Items Menu Calibration Temperature has focusMeasurement Displays Operators Manual Available Display Lines Display LineSelecting an Item and Placing It Using the APPEND, DELETE, and Insert ButtonsDisplay Line Group Selection Changing a Line on a DisplayTimer Intervals 38. The Timer Intervals FormBias Settings 39. The Bias Settings FormExamples Appending a Display Changing the Pressure UnitsCustomizing a Measurement Display Deleting a DisplayErrors Troubleshooting and Service TroubleshootingSymptom HiBias annunciator displayed Symptom Display does not light up when Power is pressedSymptom ??Bias annunciator displayed Symptom LoBias annunciator displayedBit Description Action Symptom Internal Reset Error displayedSymptom Configuration Error displayed Do not makeSymptom Bias voltage measurement changes by one digit Symptom Current Overrange DisplayedSymptom Dashes displayed instead of digits Measurements. ReturnExample 299.9 to Display Will Not Light Low Battery Hours? Is the battery voltage greater than 5.9 volts?Go to Bias ErrorLine Line Fuse Replacement Model 35040 Therapy Dosimeter Fuse ReplacementCleaning The Instrument Interface Connector CleaningReplaceable Parts Information Recalibration, Repair Information & Technical Assistance Warranty InformationReplaceable Parts List Replaceable Parts InformationBlank Sample Customization Reports Sample Documents35040 Appendix Sample Customization Reports 35040 Appendix Sample Customization Reports Blank Overview Introduction New FeaturesTimed Measurements Specifications Update Setup New Features BTimer Use Procedure Timer Setup ProcedureMaking Timed Exposure Measurements RESET/MEASURE Setup BADC ALC Automatic Leakage CompensationStart NA pA Stop Thres Current Operation Instructions BTimer Setup Decimal PlacesTable B-2. Measurement Indicators and Conditions Annunciators, Indicators, and Overrange ConditionsTable B-1. Annunciators Table B-3. Overrange Conditions Condition Overranged Measurement1Theory Of Operation Theory of OperationConfiguration Error Service Required Error Number Measurement Menu Main 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