Fluke 35040 Setting Thresholds, Predicted Timed Charge and Dose, Accumulated Charge and Dose

Page 21

Theory of Operation

2

Basic Operating Equations

Q1 represents the next sample of charge at time T1 following the activation of the timer. Q2 corresponds to the interpolated charge at time T2, where T2 is an integral number of seconds that is restricted to times within the range: T1 < T2 ≤ (T1 + Timer Interval Setting).

Predicted Timed Charge and Dose

This measurement extrapolates the timed charge (QTimed) at the elapsed time (TElapsed) that should be accumulated at completion of the timer interval (i.e., TimerIntervalSetting) based on the rate of charge delivery.

= QTimed[C] ×

QTimed_Predicted TElapsed[s] TimerIntervalSetting[s]

DoseTimed_Predicted = QTimed_Predicted [C] × ICCF [Units/C] × ADCF

At the conclusion of the timer interval (i.e., TElapsed equals the TimerIntervalSetting), the predicted timed charge and dose are equal to the predicted timed charge and dose, respectively.

Accumulated Charge and Dose

This measurement accumulates charge across multiple exposures. The displayed value is updated during the exposure and held between exposures. It is reset to zero when the RESET/MEASURE button is pressed while viewing a measurement screen.

QAccum = QAccum_previous [C] + QExposure [C]

DoseAccum = QAccum [C] × ICCF [Units/C] × ADCF

Exposure Current and Rate

The current (3-1/2 digit) and dose rate displayed when the exposure is in progress are updated once per second. The current and dose rate return to zero after the end of the exposure. The dose rate measurement is displayed using the selected time base (seconds, minutes, or hours). If the start and stop thresholds are set to zero, ILeakage is zero.

IExposure = I [A] − ILeakage [A]

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

Average Current and Rate

The average current is calculated using the charge accumulated ( Q/Ut) during a portion of the exposure to eliminate noise effects. The displayed value (4-/1/2 digit) is held following the exposure and reset at the

⎛

Q2 [C] − Q1 [C]

⎞

IAvg = ⎜

⎟

T 2 [s] − T1[s]

⎝⎜

⎠⎟

DoseRateAvg = IAvg [A] × ICCF [Units/C] × ADCF × RateMultiplier [s]

start of a subsequent exposure.

Q1 and Q2 are measured within the exposure at times T1 and T2 respectively. T1 is 1.33 seconds after the start of exposure. T2 is 1.33 seconds before the end of exposure (see Figure 2-3). The exposure must be more than 3 seconds long. IAvg is 0 if the exposure is less than 3 seconds.

2.3.1 Setting Thresholds

The instrument has capability to automatically detect the start and end of an exposure when the current crosses given limits. Using automatic detection eliminates the sag in readings that occur due to leakage

2-7

Page 20 Page 22
Image 21
Page 20 Page 22
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 Factory Calibration Error Source ± %rdg SpecificationsMaximum Error Manual AddendaFull Scale Range Display Resolution Full Scale Range Display Resolution Noise ± countsTimed Charge Measurements Current 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 DosimeterFront Panel Power SupplyMicroController Serial Communications PortElectrometer Basic Operating EquationsBias Supply Multiplexer and A/D ConverterQExposure Quantity Description Units CommentsQAccum QAccumpreviousCharge and Current Measurements Leakage Measurements= time of electrometer conversion s Timed Charge and Dose Exposure Charge and DosePredicted Timed Charge and Dose Setting ThresholdsAccumulated Charge and Dose Exposure Current and RateDoseRate = I a × Iccf Units/C × Adcf × RateMultiplier s Exposure TimeAir Density Correction Factor ⎝ PMm Hg = inch Hg x Units Display Minimum Maximum Standard Resolution ErrorSetup SetupFront Panel Familiarization IntroductionRear 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 CareBattery Care PowerOperation Instructions Front Panel ControlsPowering 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 Annunciators Reset Error With Automatic Leakage Compensation EnabledAnnunciators Annunciator ConditionIndicator Measurement Condition Measurement Indicators and Conditions? left of value Condition Overranged MeasurementCustomization Installing/Uninstalling Customization SoftwareConnection to the Computer Starting the Customization SoftwareDownloading 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 LinesDisplay Line Group Selection Using the APPEND, DELETE, and Insert ButtonsSelecting an Item and Placing It Changing a Line on a Display38. The Timer Intervals Form Timer Intervals39. The Bias Settings Form Bias SettingsExamples Customizing a Measurement Display Changing the Pressure UnitsAppending a Display Deleting a DisplayErrors Troubleshooting Troubleshooting and ServiceSymptom ??Bias annunciator displayed Symptom Display does not light up when Power is pressedSymptom HiBias annunciator displayed Symptom LoBias annunciator displayedSymptom Configuration Error displayed Symptom Internal Reset Error displayedBit Description Action Do not makeSymptom Dashes displayed instead of digits Symptom Current Overrange DisplayedSymptom Bias voltage measurement changes by one digit Measurements. ReturnExample 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 List Warranty InformationRecalibration, Repair Information & Technical Assistance Replaceable Parts InformationBlank 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
Top Page Image Contents