Fluke 35040 manual Charge and Current Measurements, Leakage Measurements

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Theory of Operation	2
Basic Operating Equations

Charge and Current Measurements

The instrument’s electrometer charge and current measurements are factory calibrated to a United States National Institute for Standards and Technology (NIST) traceable standard. Governing regulatory agencies or best of practice protocols may require that the instrument be calibrated by an independent calibration agency. The calibration agency may install the correction factors (QScaleFactor, IScaleFactor) to make the instrument read out directly as calibrated. These factors are viewable by the operator but may not be changed or turned off. In almost all cases, the scaling factors will be nearly unity.

Q= QElectrometer [C] × QScaleFactor [C/C]

⎛ Q(i )− Q(i − 1)⎞
I = ⎜		⎟	[C/s]	× IScaleFactor [A/A]

⎝⎜ T (i )−T (i − 1) ⎠⎟

T = time of electrometer conversion [s]

Leakage Measurements

Leakage measurements (QOffset , ILeakage and TOffset) are only applicable when automatic leakage compensation is enabled.

The leakage current is defined as the current present between exposures. The displayed leakage current or dose rate value (3-1/2 digit) is updated at a rate of approximately one time per second and held during an exposure. Extrapolated charge due to leakage current is nulled from the measurement. In order to do this, a short-term history of the leakage current is necessary.

When an exposure is not in progress and the absolute value of the current is less than the start threshold, pressing the RESET/MEASURE button sets the leakage current ILeakage to zero and starts the acquisition of current measurements for determining ILeakage. To get the “best” determination of ILeakage takes time, at least 10 seconds. The ion chamber, cables, and instrument should not be disturbed while making the leakage measurement.

QOffset = Q(TOffset )[C]

n

∑I [A]

ILeakage = 1

n

DoseRateLeakage = ILeakage [A] × ICCF [Units / C] × ADCF × RateMultiplier [s]

TOffset = T [s]

2-5

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Contents Therapy Dosimeter 35040Fluke 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 Manual Addenda SpecificationsFactory Calibration Error Source ± %rdg Maximum ErrorCurrent Measurements Full Scale Range Display Resolution Noise ± countsFull Scale Range Display Resolution Timed Charge MeasurementsEffective Exposure Time Measurements SpecificationsGeneral 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 QAccumLeakage Measurements Charge and Current 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 Time⎝ P Air Density Correction FactorMm 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 MessagesGeneral Considerations Basic Measurement TechniquesMaking Non-Timed Exposure Measurements Timer Use Timer Setup3Making Timed Exposure Measurements Using Other Ion Chambers Battery CareFront Panel Controls PowerBattery Care Operation InstructionsPowering 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 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 ButtonOverrange Conditions Reset ErrorCondition 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 ComputerMenu Items and Controls DownloadingCOM Port Drop Down List Close or File Close Ion ChambersFile 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 BatteryGo to Bias ErrorLine Model 35040 Therapy Dosimeter Fuse Replacement Line Fuse ReplacementCleaning The Instrument Interface Connector CleaningReplaceable 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 Overview Introduction New FeaturesTimed Measurements Specifications Update New Features B SetupTimer Use Procedure Timer Setup ProcedureMaking Timed Exposure Measurements Setup B RESET/MEASUREAutomatic Leakage Compensation ADC ALCOperation Instructions B Start NA pA Stop Thres CurrentDecimal Places Timer SetupTable B-2. Measurement Indicators and Conditions Annunciators, Indicators, and Overrange ConditionsTable B-1. Annunciators Condition Overranged Measurement1 Table B-3. Overrange ConditionsTheory 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