Fluke 90100 manual 2 300-VOLT Electronic Bias Supply, Front Panel Switches, Processor, VFD Display

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Theory of Operation

3

Overall Functional Description of the Model 35360A Tracker Display

3.2.2 300-VOLT Electronic Bias Supply

The 300 volt ionization potential is generated internally by an electronic bias supply circuit. The supply eliminates the need for the 35360A TRACKER Display to contain high voltage batteries. As explained below, the ion chamber collector and guard are maintained at the same potential as the chassis of the 35360A TRACKER Display, and the ion chamber bias plates are negatively biased at 300 VDC. A readout of the bias potential is facilitated by a divided bias signal generated within the bias supply block and connected to the A-D converter.

The output of the electronic bias supply is highly regulated and filtered. In addition, the output energy and current have been limited should the operator make direct contact. Since the bias voltage at the detector input connector is automatically discharged at power down, the operator should always turn the instrument off before attempting to make or break a connection involving the detector interface cable. During operation, the Bias Supply output level is continuously measured and verified. Any abnormal level will be indicated by an annunciator on the VFD.

3.2.3 Front Panel Switches

The nine front panel switches are of the momentary contact type, and are continuously monitored by the microcontroller for detection of contact closure. At the detection of any contact closure, the microcontroller scans the switch set to determine which key has been pressed, and then takes the appropriate action. The dedicated function of each key is described in Section 2.

3.2.4 Processor

The Processor block is based on the Motorola 68HC11 microcontroller and includes 256 KBytes of factory programmed memory (EPROM) containing all of the executable code (firmware). The revision date associated with this code is displayed during the power up sequence on the VFD. Also contained within the Processor block is 32 KBytes of RAM memory which is used to hold all volatile variables (those whose values are lost when the instrument is powered down).

A 512 byte block of nonvolatile memory (EEPROM) has also been provided. A portion of the EEPROM is automatically reprogrammed during each power down sequence to hold all of the user's front panel selections. Thus the units, front panel gain, temperature, and pressure settings in effect at power down can be automatically restored at the next power up. The EEPROM is also used to hold all of the internal electrical calibration factors for the unit, as well as all of the customization selections installed by the user over the RS-232 via the Customization program.

Besides its role as a controller of the other hardware blocks, the Processor Block performs several computational functions. It applies a number of correction factors to the displayed dose and dose rate values including the air density correction factor, the ion chamber calibration factor, the display units conversion factor, and the front panel gain settings. It also performs the ratio calculations necessary to display the percentage-of-center measurement values for the peripheral ion chambers.

3.2.5 VFD Display

All display functions are handled by a 4 line by 20 character alpha-numeric VFD module. The module is under the direct control of the microcontroller and is capable of displaying all of the user's front panel selections as well as the numerical measurement results along with their appropriate units. Other informational items including the battery and bias voltage, calibration date, and ion chamber calibration factors may be displayed. The VFD has a distinct advantage over other display technologies, such as LCD, in that it provides good visibility, and a wide viewing angle in all lighting conditions.

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Contents Tracker System ModelFluke Biomedical Table of Contents Customization Maintenance and ServiceAppendix a Using Build-Up Theory of OperationIntroduction General InformationModel FeaturesManual Addenda Before You Start Safety PrecautionsSafety Terms SpecificationsIon Chamber Factory Calibration Nominal Ion Chamber CharacteristicsMechanical Specifications Recommended Operation ConditionsElectrometer / A-D Converter Measurements ModeDisplay Mode Model 35360A Tracker DisplayEnvironment High Performance Battery ChargerUnpacking and Inspection Interface Cable Detector to DisplayOptional Equipment Standard System ContentsBlank Rear Panel Familiarization OperationDetector Input Powering the SystemDisplay. Be sure to use the correct end of the cable 3 RS-232 Computer Interface RJ-45 Style Positioning the Model 35300A Detector in the BeamOperation Positioning the Model 353300A Detector in the Beam Front Panel Controls Operation InstructionsUnits Select PowerReset Test/DetectorPowering Down the Model 35360A Tracker Display Powering Up the Model 35360A Tracker DisplayUsing the TEST/DETECTOR Button Test/Detector Screen 2 Ion Chamber Calibration Factors Using the Units Select ButtonUsing the Gain Select Button Normal Mode Using the AIR Density ButtonAbsolute Measurements Using the Measure Select Button Normal ModePercent-of-Center Measurements Underranging and Overranging Conditions Battery and Bias Annunciators24. Positions of the Battery and Bias Annunciators Gain Setting ModeAborting the Fpgf Changes Saving the Fpgf ChangesBlank Theory of Operation Hardware Block Diagram of the Model 35360A Tracker Display Power SupplyVFD Display Front Panel Switches2 300-VOLT Electronic Bias Supply ProcessorElectrometer Serial Communications PortMultiplexer and A/D Converter Air Density Corrections Model 35300A Ion Chamber DetectorsBasic Operating Equations Basic Operating Quantities Blank Maintenance & Service Problem TroubleshootingNo Display Flowchart Low battery Yes Annuciator displayed? Low Battery Indication at the Display35360A Tracker Bias Error LoBias or HiBias Indication at the DisplayLeakage Flowchart Dose Rate Measurement Zero Problem Flowchart Line Fuse ReplacementIf fuses continue to blow return instrument for repair Cleaning the Instrument Interface Connector CleaningReplaceable Parts Information Recalibration & Repair Information / Technical Assistance Replaceable Parts ListCustomization Screen Formats Make a Working DiskConnection to the Computer Starting the Customization SoftwareDisplay Customization Items Screen Appearance F10 Exit F1 Help On-Line Help for using the Customization softwareF2 Edit Item Editing F6 Print Report PrintingDefinitions Ion Chamber Calibration Factor Iccf Setting the Electrometer Gains and OffsetsCharge Gain QG Current Gain, Current Zero IG and ADZElectrometer Charge Gains QG Electrometer Current Gain IGUsage Examples Changing the Power Down IntervalChanging the ION Chamber Calibration Factor Units Input Errors ErrorsBuild-Up, Peg, and Retainer Kit Options Using Build-UpNominal Number of build-up Solid Water Appendix Fluke Biomedical
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