LUDLUM 9-3 User manual

LUDLUM MODEL 9-3
ION CHAMBER
June 2018
Serial Number 261657 and Succeeding
Serial Numbers

LUDLUM MODEL 9-3
ION CHAMBER
June 2018
Serial Number 261657 and Succeeding
Serial Numbers

MODEL9-3 TechnicalManual
i

MODEL9-3 TechnicalManual
ii
STATEMENT OF WARRANTY
Ludlum Measurements, Inc. warrants the products covered in this manual to be free of
defects due to workmanship, material, and design for a period of twelve months from
the date of delivery. The calibration of a product is warranted to be within its
specified accuracy limits at the time of shipment. In the event of instrument failure,
notify Ludlum Measurements to determine if repair, recalibration, or replacement is
required.
This warranty excludes the replacement of photomultiplier tubes, G-M and
proportional tubes, and scintillation crystals which are broken due to excessive
physical abuse or used for purposes other than intended.
There are no warranties, express or implied, including without limitation any implied
warranty of merchantability or fitness, which extend beyond the description of the
face there of. If the product does not perform as warranted herein, purchaser’s sole
remedy shall be repair or replacement, at the option of Ludlum Measurements. In no
event will Ludlum Measurements be liable for damages, lost revenue, lost wages, or
any other incidental or consequential damages, arising from the purchase, use, or
inability to use product.
RETURN OF GOODS TO MANUFACTURER
If equipment needs to be returned to Ludlum Measurements, Inc. for repair or calibration, please
send to the address below. All shipments should include documentation containing return shipping
address, customer name, telephone number, description of service requested, and all other necessary
information. Your cooperation will expedite the return of your equipment.
LUDLUM MEASUREMENTS, INC.
ATTN: REPAIR DEPARTMENT
501 OAK STREET
SWEETWATER, TX 79556
800-622-0828 325-235-5494
FAX [phone]

MODEL9-3 TechnicalManual
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Table of Contents
Introduction 1
Getting Started 2
Battery Installation 2-1
Battery Test 2-1
Instrument Test 2-2
Operational Check 2-3
Specifications 3
Identification of Controls and Functions 4
Safety Considerations and Maintenance 5
Environmental Conditions for Normal Use 5-1
Warning Markings and Symbols 5-1
Metallized Polyester (Mylar) Window Precaution 5-2
Cleaning and Maintenance Precautions 5-2
Maintenance 5-3
Recalibration 5-3
Batteries 5-3
Desiccant 5-3
Return for Repair and Calibration 5-4
Technical Theory of Operation 6
Chamber 6-1
Chamber Window 6-1
Electrometer 6-1
Range Change 6-2
Reset 6-2
Offset Adjustment 6-2
Zero Adjust 6-2

MODEL9-3 TechnicalManual
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Range Calibration 6-3
Range Changing 6-3
Power Supplies 6-3
Audio Circuit 6-4
Meter Circuit 6-4
Recycling 7
Parts List 8
Model 9-3 Ion Chamber 8-1
Main Circuit Board, Drawing 293 × 680 8-1
Electrometer Board, Drawing 293 × 670 8-4
Wiring Diagram, Drawing 293 x 525 8-5
Drawings and Diagrams 9

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Ludlum Measurements, Inc. Page 1-1 June 2018
Introduction
he Ludlum Model 9-3 is a five-range ion chamber instrument for
measuring beta-gamma radiation up to 50 R/hr. The chamber wall,
including the instrument case, is 1000 mg/cm². A 1000 mg/cm²
retractable beta shield allows beta measurement with a 7 mg/cm²
window.
The six-position selector switch selects OFF, ×10K, ×1K, ×100, ×10, and
×1. Each range has a front-panel mounted calibration control. Other
features include an audio pulsing in proportion to the meter reading,
RESET, and ZERO ADJUST. An additional calibration control “L” is
utilized to zero electrometer offset voltage.
The unit is powered by two “AA” cell batteries for operation from -20 to 50
°C (-4 to 122 °F).
Section
1
T

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Ludlum Measurements, Inc. Page 2-1 June 2018
Getting Started
Battery Installation
Ensure the Model 9-3 range selector switch is in the OFF position. Open the
battery lid by pushing down and turning the quarter-turn thumbscrew
counterclockwise one quarter of a turn. Install two “AA” size batteries in the
compartment.
Note the (+) and (-) marks inside the battery holder. Match the battery polarity
to these marks. Insert the negative end of the battery firmly against the spring
in the battery holder, then push the positive end of the battery forward to
ensure contact is made at both ends of the battery. Close the battery box lid,
then push down and turn the quarter-turn thumb screw clockwise one quarter
of a turn.
Note:
The center post of a battery is positive. The batteries are placed in
the battery compartment in opposite directions.
Battery Test
The batteries should be checked each time the instrument is turned on. This is
accomplished simply by pressing the BAT TEST button. Ensure that the meter
needle deflects to the battery test portion of the meter scale. If the meter does
not respond, check to see if the batteries have been correctly installed. Replace
the batteries if necessary.
Section
2

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Ludlum Measurements, Inc. Page 2-2 June 2018
Instrument Test
Note:
The Model 9-3 has two options for chamber wall voltage. An
internal jumper may be selected to allow continuous voltage on
the chamber wall with the instrument turned off. This option
allows a faster, three-minute settling time when the instrument is
frequently used. If the instrument is infrequently used, it is
recommended that this option not be used, because of battery
drain. Battery life with the continuous wall voltage on and
instrument off is approximately six months.
Without this option, the battery drain is zero with the instrument
OFF. When the instrument is turned on, a settling time of 5
minutes is required for a reading of less than 0.2 mR/hr, 10
minutes for less than 0.1 mR/hr, and several hours for readings
near zero.
The instrument will be shipped with the chamber wall voltage
turned on when the instrument is turned off.
After checking the batteries with the range switch on the ×10K position, turn
the instrument range switch to the ×1 position. Note that as the selector switch
moves from ×100 to ×10, a meter transient will occur. This transient is caused
by an internal range relay and is normal. Allow time for the ×1 scale to stabilize.
Open the beta shield slide. Switch the AUD ON OFF switch to ON. Expose
the chamber window to a check source. Observe that the audio click frequency
increases as the meter reading increases.
Note:
The RESET circuit discharges the chamber and opens the
chamber connection to the electrometer. This causes a transient
on the ×1 and ×10 scales. The meter will indicate full scale and
count-down for five seconds when the RESET switch is pressed
and released. For near zero reading on ×1 scale, allow several
more seconds for setting time after RESET is released.

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Ludlum Measurements, Inc. Page 2-3 June 2018
Open the beta shield and expose the check source to the center of the chamber
window. The instrument reading should be within 20% of the check source
reference after settling time.
Note:
The depressions on the side of the instrument housing indicate the center
of the chamber.
Once this procedure has been completed, the instrument is ready for use. When
using the instrument, open the beta shield for greater beta response, and close
for less.
Caution!
Damage to the metalized polyester window on the back side of the
instrument may result when the slide is open if careful instrument
handling is not practiced. The window is very fragile and may be
punctured quite easily.
Operational Check
To assure proper operation of the instrument between calibrations and periods
of non-use, an instrument operational check, including battery test and
instrument test (as described above), should be performed prior to use. A
reference reading with a check source should be obtained at the time of initial
calibration, or as soon as possible, for use in confirming proper instrument
operation. In each case, ensure a proper reading on each scale. If the instrument
fails to read within 20% of a proper reading, it should be sent to a calibration
facility for recalibration.

MODEL9-3 TechnicalManual Section3
Ludlum Measurements, Inc. Page 3-1 June 2018
Specifications
0
Range: typically 0.2-50,000 mR/hr.
Linearity: reading within 10% of true value.
Response: approximately five seconds for 90% of final meter deflection
on the ×1 scale and ×10, and two seconds on the remaining scales
Background: approximately every three minutes an up-scale “kick” may
be noted on the ×1 scale. This is due to normal cosmic background
radiation.
Chamber:
Chamber Wall Construction: carbon-coated acrylic
Chamber Volume: 220 cm3(13.4 in3)
Window: 7 mg cm2 metallized polyester
Window Area: 40 cm2 (6.2 in3) (31.5 cm2 {4.9 in2}) open with optional
79% open screen)
Beta Shield: retractable 1000 mg/cm2phenolic slide
Beta Factor with the instrument exposed to a depleted uranium slab of
234 mrad/hr:
Reading with slide open: 50 mR/hr
Reading with slide closed: 1.2 mR/hr
Thus, Beta Factor = 234 divided by (50 minus 1.2) = 4.8
Energy Response: within 20% of true value from 40 keV to 2 MeV
Battery Dependence: Instrument calibration change is less than 5%
within battery check limits on the meter.
Section
3

MODEL9-3 TechnicalManual Section 3
Ludlum Measurements, Inc. Page 3-2 June 2018
Warm-up Time: After power-up, ×100 through ×10K scales will be ready for
use in two minutes. For the ×1 scale and if the wall voltage option is on with
the instrument off, the scale will settle within 0.1 mR/hr within three minutes.
If the wall voltage option is off, allow 15 minutes for the ×1 scale to settle
within 0.1 mR/hr. Allow 30 minutes for the ×1 scale to settle to near zero in a
very low radiation field.
Magnetic Field Exposure: per ANSI 42-17A, magnetic fields of 800
A/m cause than a 15% deviation in instrument response
Instrument Controls
Multipliers: ×1, ×10, ×100, ×1K, and ×10K selected by a front-panel range
selector switch
Reset:The RESET circuit discharges the chamber and opens the chamber
connection to the electrometer. This causes a transient on the ×1 and ×10
scales. The meter will indicate full scale and count-down for five seconds when
the RESET switch is pressed and released. For near zero reading on ×1 scale,
allow several more seconds for setting time after RESET is released.
Battery Check: At 2.0 Vdc, the meter needle will drop to the edge of
the BAT OK area when the BAT TEST pushbutton is pressed. The audio
circuit will start clicking when the battery voltage drops to 1.9 V.
Zero Adjust: a control allowing limited background subtract and an
external one-turn potentiometer, also used to compensate electrometer
drift
Calibration Controls: individual potentiometers for each range;
accessible from the front cover while in operational status
Meter: 6.4 cm (2.5 in.) arc, 1 mA, pivot-and-jewel suspension
Meter Dial: 0-5 mR/hr, BAT TEST
Audio: built-in unimorph speaker with ON-OFF switch (greater than 60
dB at 61 cm {2 ft})
Power: two “AA” cell batteries housed in a sealed externally accessible
compartment
Battery Life: ×100 and higher ranges at full scale without display light, 1050
hours; at ×1 and ×10 in low background without display light, 1500 hours
Construction: cast-and-drawn aluminum with beige powder coating

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Temperature Range: -20 to 50 °C (-4 to 122 °F)
Dimensions: 23.4 x 8.9 x 21.6 cm (9.2 x 3.5 x 8.5 in.), including instrument
handle
Weight: 1.6 kg (3.6 lb), including batteries

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Ludlum Measurements, Inc. Page 4-1 June 2018
Identification of Controls and
Functions
Range Selector Switch: This is a six-position switch marked OFF,
×10K, ×1K, ×100, ×10, and ×1. Turning the range selector switch from
OFF to one of the range multiplier positions (×10K, ×1K, ×100, ×10,
and × 1) provides the operator with an overall range of 0 to 50,000
mR/hr. Multiply the scale reading by the multiplier to determine the
actual scale reading.
BAT TEST: Press this switch to check the battery. The meter should read
within the BAT TEST scale on the meter. The range switch may be in
any position except OFF for the battery test.
AUD ON-OFF Toggle Switch: In the ON position, this switch energizes
the unimorph speaker, located on the left side of the instrument. The
frequency of the clicks is relative to the meter reading; the higher the
reading, the higher the audio frequency.
ZERO ADJUST: This is a full one-turn control that allows for
compensation of electrometer drift. Press and hold the RESET button
until the meter counts down, then adjust for a zero reading.
Range Calibration Adjustments: recessed potentiometers located under
the calibration cover, on the right side of the front panel. These
adjustment controls allow for individual calibration of each range
multiplier, and are labeled 1, 10, 100, 1K, and 10K
L: Recessed potentiometer located under the calibration cover; used to
adjust the meter to zero before the ZERO ADJUST is adjusted for a zero
meter reading with the RESET button depressed. Set range switch to
×100 and move the instrument to an area of low radiation and adjust L
for a meter reading of zero.
RESET Button:The RESET circuit discharges the chamber and opens the
chamber connection to the electrometer. This causes a transient on the ×1 and
×10 scales. The meter will indicate full scale and count-down for five seconds
Section
4

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when the RESET switch is pressed and released. For near zero reading on ×1
scale, allow several more seconds for setting time after RESET is released
Beta Shield (on bottom): A retractable shield allowing exposure to beta
radiation with a window thickness of 7 mg/cm². With the slide closed,
the window is 1000 mg/cm². Depress the button on the side of the slide
assembly to release the slide. Release the button to hold the slide open
or closed.

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Safety Considerations and
Maintenance
Environmental Conditions for Normal Use
Indoor or outdoor use
Altitude dependant: Response decreases 3% for every increase in 1000 feet of
elevation above the calibration elevation. (For further information, see the
Average Model 9 Altitude Dependence graph in Section 9 of this manual).
Temperature range of -20 to 50 °C (-4 to 122 °F)
Maximum relative humidity of less than 95% (non-condensing)
Pollution Degree 3 (as defined by IEC 664) (Occurs when conductive pollution
or dry nonconductive pollution becomes conductive due to condensation. This
is typical of industrial or construction sites.)
Warning Markings and Symbols
Caution!
The operator or responsible body is cautioned that the
protection provided by the equipment may be impaired if the
equipment is used in a manner not specified by Ludlum
Measurements, Inc.
The Model 9-3 Ion Chamber is marked with the
following symbols:
The “crossed-out wheelie bin” symbol notifies the consumer that the
product is not to be mixed with unsorted municipal waste when discarding;
each material must be separated. The symbol is placed on the battery
compartment lid. See section 7, “Recycling,” for further information.
Section
5

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Ludlum Measurements, Inc. Page 5-2 June 2018
Warning!
The operator is strongly cautioned to take the following
precautions to avoid contact with internal hazardous live parts
that are accessible using a tool:
1. Turn the instrument power OFF and remove the batteries.
2. Allow the instrument to discharge before accessing internal
components. The 90-volt wall voltage will require several
hours to discharge. It may be discharged with a 10 megohm
resistor.
Metalized Polyester (Mylar)
Window Precaution
Caution!
Damage to the metalized polyester window on the back side of
the instrument may result if careful instrument handling is not
practiced. The window is very fragile and may be punctured
quite easily.
Cleaning and Maintenance Precautions
Instrument maintenance consists of keeping the instrument clean and
periodically checking the batteries, desiccants, and calibration. The Model 9-
3 (excluding chamber window) may be cleaned externally with a damp cloth,
using only water as the wetting agent. Do not immerse the instrument in any
liquid. Observe the following precautions when cleaning or performing
maintenance on the instrument:
1. Turn the instrument OFF and remove the batteries.
2. Allow the instrument to sit for one minute before cleaning the
exterior or accessing any internal components for maintenance.
3. Discharge the wall voltage with a 10 megohm resistor, or allow
several hours for discharge if the instrument is opened.

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Ludlum Measurements, Inc. Page 5-3 June 2018
Maintenance
RECALIBRATION
Recalibration should be accomplished after maintenance or adjustments
have been performed on the instrument. Recalibration is not normally
required following instrument cleaning, desiccant servicing or battery
replacement
Note:
Ludlum Measurements, Inc. recommends recalibration at
intervals no greater than one year. Check the appropriate
regulations to determine required recalibration intervals.
Ludlum Measurements offers a full-service repair and calibration
department. We not only repair and calibrate our own instruments, but also
most other manufacturers’instruments. Calibration procedures are available
upon request for customers who choose to calibrate their own instruments.
BATTERIES
The batteries should be removed any time the instrument is placed into
storage. Battery leakage may cause corrosion on the battery contacts, which
must be scraped off and/or washed using a paste solution made from
baking soda and water.
DESICCANT
Remove the instrument can and observe the translucent plastic desiccant
box. If the desiccant is blue, close the can and use the instrument. If the
desiccant is pink, replace with a fresh box. The restraining strap may be
loosened by pressing the center tab toward the strap.
The pink (wet) desiccant may be recycled by placing it in an oven at 55 °C
(131 °F) for two hours, or in a microwave on the HI setting for 10 seconds.
If water vapor is apparent, wipe off the water and heat for another 10
seconds. Repeat until the box and desiccant appear dry. When fully dried
out, the desiccant will be blue in color.

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Ludlum Measurements, Inc. Page 5-4 June 2018
Caution!
The desiccant box will be HOT when removed from the
microwave or oven!
If the instrument is stored in an area with high humidity, rapid changes in
temperature should be avoided. A storage cabinet with a light bulb inside is
one means of keeping the instrument in a slightly warmer than ambient
temperature environment, in order to prevent problems from rapid changes
in temperature and humidity.
Return for Repair or Calibration
To return an instrument for repair or recalibration, provide sufficient
Return Form, which can be downloaded from the Ludlum website at
www.ludlums.com. Find the form by clicking the “Support” tab and
selecting “Repair and Calibration” from the drop-down menu. Then choose
the appropriate Repair and Calibration dvision where you will find a link to
the form.

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Technical Theory of Operation
Chamber
The chamber housing is constructed from acrylic and is coated inside and
outside with carbon. The internal wall is maintained at approximately 90
volts. The external wall is at ground potential.
The electrode is connected to the electrometer input and is maintained at
ground potential by the electrometer.
Chamber Window
The chamber window consists of three parts. The beta shield is 1000
mg/cm²phenolic. One layer of 3.5 mg/cm²metallized polyester is glued to
the bottom of the can and one layer of 3.5 mg/cm²metalized polyester
covers the ion chamber, resulting in a window thickness of 7 mg/cm²with
the beta slide open, and a 1000 mg/cm2window with the beta slide closed.
Electrometer
The electrometer consists of U1, R2, and supporting components. On
the ×1 scale, RL1 and RL2 are open. With conduction in the chamber to
the negative wall, pin 8 of U1 goes slightly negative causing pin 4 of U1
to go positive, drawing current through R2, holding pin 8 of U1 near the
guard voltage (+1.5 volts).
With the chamber exposed to a 5 mR/hr field, the chamber current will
be approximately 70 fA (70 x 10-15 amps) and electrometer output
voltage will be 35 mV (0.035 V) relative to the guard voltage. At 50
mR/hr on the x10 range, the output voltage will be 350 mV (0.35 V)
relative to the guard voltage.
Section
6