RADIOLOGICAL SURVEY METEROCDM ITEM NO. CD V-715, MODEL 1

.MANUFACTURED BY

LIONEL ELECTRONIC LABORATORIES, INC.BROOKLYN 37, NEW YORK

1961-62

CONTENTSTABLE OF

SECTION 1.GENERAL DESCRIPTION

SECTION 6.PREVENTIVE MAINTENANCE

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Paragraph

6.1 Battery Life 6.2 Storage 6.3 Battery Inspection

Paragraph1.1 Introduction 1.2 Ranges 1.3 Spectral Response

1.4 Accuracy 1.5 Controls 1.6 Circuit Check 1.7 Batteries 1.8 Meter 1.9 Physical Features.

SECTION 7.CORRECTIVE MAINTENANCE

7

999

SECTION 2.THEORY OF OPERATION

2.1 Introduction 32.2 Ionization Chamber 52.3 Electrometer Tube 52.4 Measuring Circuit 52.5 Power Supply 5

2_5.1 The High Voltage Supply 5

9

7.1 Calibration 7.2 Disassembly for

Corrective Maintenance.7.3 In Case of Difficulty 7.4 Checking Power Supply.

7.5 Checking Electrometer

Tube 7.6 Checking Ionization

Chamber 9

SECTION 8.REPLACEMENT PARTS LIST

SECTION 3.INSTALLATION 12

1313

8.1 Electrical Components ..-

8.2 Mechanical Components8.3 Vendors3.1 Installing the Batteries. 6

SECTION 4.OPERATION LIST OF IllUSTRATIONS

Figure Page

66

4.1 Operating the Unit theFirst Time 4.1 Reading the Instrument.

248

2.3.4.

Title ]

Lionel CD V-715 Survey

Meter Calibration Adjustment Interior Details Printed Wiring Board and

Component Location Schematic for V-715

SECTION S.OPERATORS MAINTENANCE

10117 5.5.1 Battery Replacement

1

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Fig- l-Lionel CDV-715 Survey Meter

2

I. GENERAL DESCRIPTION1.1 INTRODUCTION

The 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 RANGES

Four 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 RESPONSE

The error introduced by changes in energy level from .08 MEV(Million Electron Volts) to 1.2 MEV is less than 15%.1.4 ACCURACY

The 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 CONTROLS

Two 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 CHECK

The 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.1.7 BATTERIES

One "D" size flashlight cell is used (NEDA type 13). The usefuloperating life is a minimum of 150 hour for continuous duty andsomewhat longer for intermittent use.

1.8 MEYERThe meter is a core magnet type of movement, semi ruggedized

to withstand shock, vibration and rough field handling.1.9 PHYSICAL FEATURES

The instrument is approximately 4lf2 inches wide, 8% incheslong and 7 inches high including the handle and weighs 4 lbs. It isfinished in bright yellow baked enamel. The panel is die cast zincand the case drawn aluminum. The handle it! also die cast zinccontoured to comfortably fit the hand.

2. THEORY OF OPERATION2.1 INTRODUCTION

This instrument consists of an ionization chamber, electrometer~

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Fig. 2-Calibration Adjustment

4

tube and a transistorized power supply. Intensity of radiation isiudicated ou a 31f2 inch panel meter. See fig. 22.2 IONIZATION CHAMBER

The 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 ELECTROMETER TUBEThe 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 in

current 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 the 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 decreasein tube current and the indicating meter reads up scale by an amountproportional to the Radiation Intensity. Resistors R 10 through R 13are calibrating potentiometers for the various ranges and they shuntsome of the current around the meter. Resistors R 6 through R 9 arein series with the chamber on the various ranges. They act as voltagedeveloping resistors for the four instrument ranges. R 4 is switchedout of the circuit in the check position by switch S-IC. This changesthe bias on V 1 and serves to make the meter read up scale in thecheck position.2.5 POWER SUPPLY

2.5.1 THE HIGH VOLTAGE SUPPLYThe high voltage supply consists of a blocking oscillator circuit

in which pulses are generated by a transistor, Q-l alternately cut-offand saturated. The transformer windings between the base andcollector are so phased that when the collector current starts to flow,the voltage at the base goes in the negative direction. By virtue of thebase going negative, the collector current will increase still further

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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 BAnERY

The 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.

4. OPERATION4.1 OPERATING THE UNIT THE FIRST TIME

Turn the range switch to the Zero position, wait two minutesfor the electrometer tube to warm up and adjust the Zero Control tobring the meter to zero.

Turn the range switch to the Check position. The meter shouldread within the red markings designated Circuit Check. If it does not,the battery may be dead or trouble may exist in the circuit. Seesection 5 and 7 for maintenance procedures. When the battery is new,the meter should read within the circuit check band. When thereading nears the bottom of the check band the battery should bereplaced. Operators maintenance should be limited to replacementof the battery.

4.2 READING THE INSTRUMENTTurn the range switch to the X100, X10, Xl or XO.1 range as

required and read the radiation intensity on the meter. The meterreadings must be multiplied by the factor for the range being used.

6

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 REPLACEMENT

The 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. PREVENTIVE MAINTENANCE6.1 BAnERY LIFE

Caution: 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 should

be 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

(WARNING: Calibration should only be done by personneltrained in the use of X.Ray generators and radioactive isotopes.)

The CD V.715 is calibrated by being placed in a gamma radiationfield of known intensity. Fields of this type may be produced by anX.Ray machine, radium, cobalt 60 or cesium 137. As an example a100 MC. radium source will produce a radiation intensity of .40R/HR, at a distance of 18.1 inches. The CD V.715 when set-to theXO.l range and so positioned should read this intensity. If it doesnot the instrument should be recalibrated. Since each range of theinstrument has its own calibration control (See Fig. 2) suitable fieldsfor each range must be available. The X.O.l range is calibrated byadjusting R 10 similarly R II adjusts X.l, R 12 adjusts X.I0 andR 18 adjusts X-IOO. See fig. 2 and 3

The instrument may be calibrated outside of its case if a gammafield such as obtained from Cesium 137 or Cobalt 60 is used. On softX.Rays, the instrument should be in the case when calibration ischecked. Geometry also must be considered. Errors may be introduced

..

ELECTROMETER

TUBECALIBRATION

CONTROLSZERO

ADJUST

.CHAMBERHEADERADJUST

'(0 ,-,'I J', 0 ~0 0,.I C

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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. Remove

the 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 looseningthe 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 DIFFICULTYOpen 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 a

voltmeter having a sensitivity of 20,000 ohms per volt or higher.1. Check the battery with the instrument turned on. The 1.5 volt

supply 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 voltagesare low, check the voltage at the collector of transistor Q-1.This voltages should be at least -0.7 volts with respect to theemitter. If the voltage is low replace Ql. If the collectorvoltage is sufficiently high replace either or both rectifiersDl and D2.

7.5 CHECKING ELECTROMETER TUBEThis check can best be accomplished by removing the battery

and checking the resistance across the filaments. This should be lessthan 200 ohms.

7.6 CHECKING IONIZATION CHAMBERInspect chamber header for presence of dirt or solder flux.

Measure resistance of header to outside of chamber. Resistance asmeasured on an ohmmeter capable of measuring 1000 megohmsshould be infinite. If ohmmeter indicates, the chamber is damaged.Care must be exercised in high humidity so as not to be mislead bylow resistance readings. The chamber should be checked in a dryenvironment.

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