Exposure Charge and Dose, Timed Charge and Dose | Fluke 35040

35040

Operators Manual

Charge

QOffset	X X	X
0
	TOffset	TStart	Time
	Start of Exposure
- Charge samples in Leakage.
X -	Samples discarded.
-	Charge samples in exposure.
-	Extrapolated charge due to leakage current

Figure 2-2.Leakage Current and Start of Exposure

When automatic exposure detection is disabled (start and stop threshold set to 0.0 pA), there is no correction for extrapolated charge due to leakage current. The dosimeter must be manually reset between exposures and the leakage current kept as low as possible for best results.

Exposure Charge and Dose

The charge on the electrometer during an exposure is due to the incident radiation plus the charge that was on the electrometer before the exposure plus the extrapolated charge due to any leakage currents in the ion chamber, cables, or electrometer. To obtain only the charge due to the exposure, the instrument employs the following equation:

QExposure = Q [C] − QOffset [C] − (ILeakage [A] × (T [s] −TOffset [s]))

Dose = QExposure [C] × ICCF [Units/C] × ADCF

The exposure charge variable QExposure is set to zero at the start of an exposure either manually by pressing the RESET/MEASURE button or automatically if the start and stop thresholds are used. Over the duration of the exposure, QExposure and Dose are updated about once a second. The displayed measurement value (4-1/2 digit) is held following the exposure.

Timed Charge and Dose

This measurement accumulates charge only while the elapsed time is less than or equal to the timer interval setting. The displayed value is held following the completion of the timer interval.

QTimed = Q2[C] − Q1 [C] − (ILeakage [A] × (T 2 [s] − T 1 [s]))

DoseTimed = QTimed [C] × ICCF [Units/C] × ADCF

2-6

Image 20

Fluke 35040 manual Exposure Charge and Dose, Timed Charge and Dose

Contents

35040 Therapy Dosimeter Fluke Biomedical Table of Contents Sample Customization Reports Troubleshooting and ServiceAddendum Features of Firmware Version 27JAN00 or Later Iii Blank Introduction FeaturesIntroduction Operators Manual Before You Start Safety PrecautionsSafety Symbols And Terms Specifications Factory Calibration Error Source ± %rdgMaximum Error Manual Addenda Full Scale Range Display Resolution Noise ± counts Full Scale Range Display ResolutionTimed Charge Measurements Current Measurements General Measurements SpecificationsEffective Exposure Time Measurements High Performance Power Supply and Battery Charger Unpacking and Inspection 35040 Hardware Block Diagram of the Model 35040 Therapy Dosimeter Functional Description Power Supply Front PanelMicroController Serial Communications Port Basic Operating Equations ElectrometerBias Supply Multiplexer and A/D Converter Quantity Description Units Comments QExposureQAccum QAccumprevious = time of electrometer conversion s Charge and Current MeasurementsLeakage Measurements Exposure Charge and Dose Timed Charge and Dose Setting Thresholds Predicted Timed Charge and DoseAccumulated Charge and Dose Exposure Current and Rate Exposure Time DoseRate = I a × Iccf Units/C × Adcf × RateMultiplier s Mm Hg = inch Hg x Air Density Correction Factor⎝ P Standard Resolution Error Units Display Minimum Maximum Setup SetupFront Panel Familiarization Introduction Powering The System Rear Panel Familiarization Power-Up Self-Test and Display Messages Ion Chamber Connector Making Non-Timed Exposure Measurements Basic Measurement TechniquesGeneral Considerations 3Making Timed Exposure Measurements Timer SetupTimer Use Battery Care Using Other Ion Chambers Power Battery CareOperation Instructions Front Panel Controls Powering Up the Model 35040 Therapy Dosimeter Operation Instructions Powering Down the Model 35040 Therapy DosimeterUsing the Test Function Button QScaleFactor=1.0000 IScaleFactor=1.0000 12. The Test Function Screen Showing the Timer Settings 5Automatic Leakage Compensation Calibrated by Keithley RMD Nov 15 6Timer Setup 17. The Test Function Screen Showing the Timer Settings Using the Detector Select Button Using the AIR Density Button Using the Units Select Button Using the Bias Select Button Set 300.0 V 100% Central Electrde Pos IC Bias 300.0 V CEP Using the RESET/MEASURE Button Overranging Conditions Condition Values Overranged Reset ErrorOverrange Conditions Reset Error With Automatic Leakage Compensation Enabled AnnunciatorsAnnunciators Annunciator Condition Measurement Indicators and Conditions Indicator Measurement Condition? left of value Condition Overranged Measurement Installing/Uninstalling Customization Software CustomizationConnection to the Computer Starting the Customization Software COM Port Drop Down List DownloadingMenu Items and Controls File Save AS and File Print Ion ChambersClose or File Close Edit OK and Cancel Special Items Download and Cancel 36. The Special Items Menu Calibration Temperature has focus Measurement Displays Operators Manual Available Display Lines Display Line Using the APPEND, DELETE, and Insert Buttons Display Line Group SelectionSelecting an Item and Placing It Changing a Line on a Display Timer Intervals 38. The Timer Intervals Form Bias Settings 39. The Bias Settings Form Examples Changing the Pressure Units Customizing a Measurement DisplayAppending a Display Deleting a Display Errors Troubleshooting and Service Troubleshooting Symptom Display does not light up when Power is pressed Symptom ??Bias annunciator displayedSymptom HiBias annunciator displayed Symptom LoBias annunciator displayed Symptom Internal Reset Error displayed Symptom Configuration Error displayedBit Description Action Do not make Symptom Current Overrange Displayed Symptom Dashes displayed instead of digitsSymptom Bias voltage measurement changes by one digit Measurements. Return Example 299.9 to Display Will Not Light Low Battery Hours? Is the battery voltage greater than 5.9 volts? Line Bias ErrorGo to Line Fuse Replacement Model 35040 Therapy Dosimeter Fuse Replacement Replaceable Parts Information Interface Connector CleaningCleaning The Instrument Warranty Information Replaceable Parts ListRecalibration, Repair Information & Technical Assistance Replaceable Parts Information Blank Sample Customization Reports Sample Documents 35040 Appendix Sample Customization Reports 35040 Appendix Sample Customization Reports Blank Timed Measurements Introduction New FeaturesOverview Specifications Update Setup New Features B Making Timed Exposure Measurements Timer Setup ProcedureTimer Use Procedure RESET/MEASURE Setup B ADC ALC Automatic Leakage Compensation Start NA pA Stop Thres Current Operation Instructions B Timer Setup Decimal Places Table B-1. Annunciators Annunciators, Indicators, and Overrange ConditionsTable B-2. Measurement Indicators and Conditions Table B-3. Overrange Conditions Condition Overranged Measurement1 Theory Of Operation Theory of Operation Configuration Error Service Required Error Number Measurement Displays Main MenuMeasurement Menu 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