Exposure Time | Fluke 35040 specification

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

Image 22

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

Contents

35040 Therapy Dosimeter Fluke 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 Addenda Timed Charge Measurements Full Scale Range Display Resolution Noise ± countsFull Scale Range Display Resolution Current Measurements Effective 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 Description MicroController Power SupplyFront Panel Serial Communications Port Bias Supply Basic Operating EquationsElectrometer Multiplexer and A/D Converter QAccum Quantity Description Units CommentsQExposure QAccumprevious Leakage Measurements Charge and Current Measurements= time of electrometer conversion s Exposure Charge and Dose Timed Charge and Dose Accumulated Charge and Dose Setting ThresholdsPredicted Timed Charge and Dose Exposure Current and Rate Exposure 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 Maximum Front Panel Familiarization SetupSetup Introduction Powering The System Rear Panel Familiarization Power-Up Self-Test and Display Messages Ion Chamber Connector General Considerations Basic Measurement TechniquesMaking Non-Timed Exposure Measurements Timer Use Timer Setup3Making Timed Exposure Measurements Battery Care Using Other Ion Chambers Operation Instructions PowerBattery Care Front Panel Controls Powering 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 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 Overrange 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 Measurement Connection to the Computer Installing/Uninstalling Customization SoftwareCustomization Starting the Customization Software Menu Items and Controls DownloadingCOM Port Drop Down List Close or File Close Ion ChambersFile Save AS and File Print 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 Selecting an Item and Placing It Using the APPEND, DELETE, and Insert ButtonsDisplay Line Group Selection Changing a Line on a Display Timer Intervals 38. The Timer Intervals Form Bias Settings 39. The Bias Settings Form Examples Appending a Display Changing the Pressure UnitsCustomizing a Measurement Display Deleting a Display Errors Troubleshooting and Service Troubleshooting Symptom HiBias annunciator displayed Symptom Display does not light up when Power is pressedSymptom ??Bias annunciator displayed Symptom LoBias annunciator displayed Bit Description Action Symptom Internal Reset Error displayedSymptom Configuration Error displayed Do not make Symptom Bias voltage measurement changes by one digit Symptom Current Overrange DisplayedSymptom Dashes displayed instead of digits Measurements. Return Example 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 Replacement Cleaning The Instrument Interface Connector CleaningReplaceable Parts Information Recalibration, Repair Information & Technical Assistance Warranty InformationReplaceable Parts List Replaceable Parts Information Blank Sample Customization Reports Sample Documents 35040 Appendix Sample Customization Reports 35040 Appendix Sample Customization Reports Blank Overview Introduction New FeaturesTimed Measurements Specifications Update Setup New Features B Timer Use Procedure Timer Setup ProcedureMaking Timed Exposure Measurements RESET/MEASURE Setup B ADC ALC Automatic Leakage Compensation Start NA pA Stop Thres Current Operation Instructions B Timer Setup Decimal Places Table B-2. Measurement Indicators and Conditions Annunciators, Indicators, and Overrange ConditionsTable B-1. Annunciators Table B-3. Overrange Conditions Condition Overranged Measurement1 Theory Of Operation Theory of Operation Configuration 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