Lionel 715-1 - Radiologic Survey Meter.pdf

7/29/2019 Lionel 715-1 - Radiologic Survey Meter.pdf

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RADIOLOGICAL URVEYMETEROCDMTEMNO.CDV-715,MODEL

.MANUFACTUREDYLIONEL ELECTRONIC LABORATORIES, INC.BROOKLYN37, NEW YORK

1961-62


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CONTENTSABLE OFSECTION .GENERALDESCRIPTION SECTION 6.PREVENTIVEMAINTENANCE

P3Jge- 3- 3. 3- 3- 3- 3- 3- 3. 3

P~e7.,

Paragraph6.2 Sorage.3 Battery Inspection

Paragraph1.3 Spectral Response

1.9 Physical Features.

SECTION .CORRECTIVEAINTENANCE

7999

SECTION2.THEORYOF OPERATION

2.1 Introduction 32.2 Ionization Chamber 52.3 Electrometer ube 52.4 Measuring Circuit 52.5 Power Supply 52_5.1 The High Voltage Supply 5

9

7.2 Disassembly forCorrective Maintenance.

7.4 Checking Power Supply.7.5 Checking Electrometer7.6 Checking Ionization

Chamber 9

SECTION 8.REPLACEMENT PARTS LISTSECTION3.


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I. GENERAL DESCRIPTION1.1 INTRODUCTIONThe Lionel V-715 is a portable, battery powered, transistorizedsurvey meter using a plated steel, hermetically sealed ionizationchamber as the detector. The chamber is mounted inside the case.The instrument and its accessories include a printed circuit board,ionization chamber, carrying strap and strap fastener. The case iswatertight to withstand immersion. (See Fig. I)1.2 RANGESFour ranges are provided, 0-.5, 0.5, 0-50 and 0-500 R/RH. On thelowest range, the smallest division on the scale is .01 R/HR.Intensities higher than 500 R/HR are indicated by the meter readingoff scale. The instrument is not harmed by this.1.3 SPECTRAL RESPONSEThe error introduced by changes n energy level from .08 MEV

(Million Electron Volts) to 1.2 MEV is less than 15%.1.4 ACCURACYThe accuracy of this instrument is plus or minus 20 percent oftrue dose rate in Cobalt 60 and or Cesium 137 gamma radiation fieldsincident normal to the bottom and normal to the front of the instru.ment. Accuracy is not affected by altitude and light or radiofrequency radiations.1.5 CONTROLSTwo controls are provided (See Fig. I). The Range Switch isused to turn on the instrument, check its proper functioning, andselect the required range. The Zero Control is used to adjust themeter to zero each time before use.1.6 CI,iCUIT CHECKThe proper functioning of the measuring circuit including thebattery may be checked by setting the range switch to Circuit Checkand observing the meter reading. The limits of acceptable indicationcover the top 30 percent of the scale. This is a reliable indication ofthe condition of the instrument.


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tube and a transistorized power supply. Intensity of radiation isiudicated ou a 31f2 nch panel meter. See fig. 22.2 IONIZATION CHAMBERThe sensing element is a hermetically sealed air equivalentionization chamber. This chamber consists of a shell and centercollector or electrode. The collector is insulated from the shell by ahigh resistance feed thru insulator. A voltage is applied between thecollector and the shell. This makes the shell 20 volts negative withrespect to the collector.Gamma radiation, in passing through the air contained in thechamber causes air molecules to become charged or ionized. Positiveions or positive charged particles are attracted to the chamber shellwhich has an opposite charge and vice versa.The arrival of these ions at the shell of the chamber, causes aflow of current whose magnitude is proportional to the number ofions collected. Since the number of ions collected is proportionalto the radiation intensity, the ionization current must be propor-tional to the radiation intensity at the ionization chamber.2.3 ELECTROMETERTUBEThe very small ionization current from the chamber collector at.5 R/HR flows through a high ohm age resistor (2xl011 ohms) anddevelops a measurable voltage across the resistor. This voltage is alsoapplied to the grid of VI 5886 Electrometer Tube which is connectedas a triode. The filament of this tube is heated by the I1f2 volt "D"Cell. The flow of electrons from the heated filament is controlled bythe voltage applied to the grid and also the voltage to the plate.2.4 MEASURING CIRCUITA 50 micro ampere meter M 1 is used to measure the change incurrent through tube V 1. Resistors R 3 and R 4 act as bias resistorsto bias V 1. Resistor R 1 the zero adjust control sets he plate voltageso that the tube current is equal to the current flowing in the meterdue to the battery and series resistor R 14. The meter M 1 then readszero. When the ionization chamber is exposed to radiation a negativevoltage is developed across R 6. This voltage results in a decrease


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causing the base to go more negative. The collector current increasesuntil the transistor demanded by the signal at the base. At this point,supply the current demanded by the signal at the base. At this point,since there is no rate of change of current in the transformer, thereis no signal induced in the base winding. When the signal is removedin the base circuit the collector current decreases and there is aresultant positive signal on the base. The transistor is cut off and anegative pulse is developed at the collector of the transistor. Thetransistor remains cut off as long as the positive signal on the baseis present. When the field in the transformer core has collapsed,the base signal is gone and the transistor starts to conduct again andanother full cycle from cut off to saturation to cut off follows.The step-up turns ratio between the collector winding and thesecondary winding produces voltage pulses which are then rectifiedby rectifiers CR1 and CR2.Since the transformer is tapped, two voltages of opposite polarityappear. The turns ratio of T 1 is such as make these voltages + 10volts and -20 volts. The plus 10 volts supplies plate voltage to theelectrometer tube and the -20 volts fixes the operating level of thechamber. Capacitors C 1 and C2 serve as capacitive filters for thetwo voltage supplies.Potentiometer~ R 16 is a factory adjustment. It serves to com-pensate for small drift in the instrument zero on the X-0.1 range.

3. INSTALLATION3.1 INSTALLING THE BAnERYThe instruments are shipped with the battery packed separately.To put the instrument into operation:1. Open the case by releasing the clamps at both ends, andremove the lid assembly.2. Remove the battery from its package, taking care not todrop it.3. Place the "D" Cell in the battery holder positive end first.The housing is designed to assure correct polarity.


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Example: A meter reading of 3.5 on the XO.l range indicates aradiation field of O.lx 3.5 or 0.35 R/HR. The indicator lines on thesides and front of the unit indicate the center line of the chamber.5. OPERATORS MAINTENANCE5.1 BATTERY REPLACEMENTThe battery should be replaced when the Circuit Check settingon the range switch makes the meter read near the low end of thecircuit check band.Remove the instrument from the case by opening two catches.Remove battery from holder and install batte;ry as outlined insection 4.6. PREVENTIVEMAINTENANCE6.1 BAnERY LIFECaution: Make certain the instrument is turned off whenever notin use. The Off Position places the index mark on the range switchperpendicular to the handle. The life of the battery is at least 150hours under continuous use; for intermittent use the life is somewhatmore.6.2 STORAGEThe instruments are shipped in a packing container and shouldbe left this way until ready to be put into operation. This preventsthe accumulation of dirt, moisture, and radioactive contamination,which would interfere with proper operation of the instrument. Forstorage purposes it is best, wherever possible, to keep the instrumentin a moderately cool area, as this will provide greater shelf life forthe battery. The instruments should not be stored with the batteryinstalled.6.3 BATTERY INSPECTION

Even under continuous use with leak.proof cells, it is advisableto check the batteries for leakage at least once per month.7. CORRECTIVE MAINTENANCE7.1 CALIBRATION


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ELECTROMETERTUBEALIBRATIONCONTROLSEROADJUST


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if the ionization chamber is brought close to the source of radiationso that parts of the chamber are not uniformly exposed to theradiation.7.2 DISASSEMBLY FOR CORRECTIVE MAINTENANCEFirst remove instrument from case and remove battery. Removethe range knob and zero knob by loosening the set screws and pullingthe knobs off shafts. Loosen and remove 6 screws holding printedcircuit board and chamber to the panel. Pull assembly free frompanel being careful not to crack the printed circuit board or damagelead from chamber. The dust cover can be removed by loosening

the hexagonal nut on the switch. This exposes all of the electroniccomponents for servicing. Chamber may be separated from theassembly by pulling clip loose. The ionization chamber header, theceramic switch section, resistors R6, R7, R8, R9 and the electrometertube require special precautions. These components are all part of avery high resistance circuit. They should not be handled except forreplacement. They should be touched only with clean tools and shouldbe cleaned afterward with clean alcohol and a clean soft brush.Solder flux and finger prints should be avoided otherwise surfaceleakage will result.Circuit troubles may be traced by reference to the circuit diagramFig. 5. Voltage measurements are with respect to ground and areobtained with a voltmeter having a sensitivity of 20,000 ohms pervolt. Such voltage checks should be made with the range switchset at zero and the Zero Adjust adjusted so that the meter reads zero.7.3 IN CASE OF DIFFICULTY

Open case and make a visual inspection for shorts, broken wires,and obviously damaged or broken components.7.4 CHECKING POWER SUPPLYMeasurements in the voltage supply should be made with avoltmeter having a sensitivity of 20,000 ohms per volt or higher.1. Check the battery with the instrument turned on. The 1.5 voltsupply should read at least 0.9 volt.2. Check the voltage across C1 and C2, it should read approx-imately +9 volts and -20 volts respectively. If these voltages


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Lionel 715-1 - Radiologic Survey Meter.pdf

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