Ludlum Measurements 12SA User manual

LUDLUM MODEL 12SA
SURVEY METER
July 2020
Serial Number 349200 and Succeeding
Serial Numbers

LUDLUM MODEL 12SA
SURVEY METER
July 2020
Serial Number 349200 and Succeeding
Serial Numbers

Ludlum Measurements, Inc. July 2020
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]

Ludlum Measurements, Inc. July 2020
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Battery Test 2-2
Operational Check 2-2
Surveying for Radiation 2-3
Background and Man-made Radiation 2-3
Radiation Limits 2-4
Suggested Survey Technique 2-4
Range Selector and Actual Measurement 2-4
False Alarms 2-5
Specifications 3
Identification of Controls and Functions 4
Safety Considerations 5
Environmental Conditions for Normal Use 5-1
Warning Markings and Symbols 5-1
Cleaning and Maintenance Precautions 5-2
Maintenance 6
Recalibration 6-1
Batteries 6-2
Technical Theory of Operation 7
Input 7-1
Amplifier 7-1
Discriminator 7-1
Scale Ranging 7-1
Digital Analog Converter 7-1
Audio 7-2
Meter Drive 7-2

Model12SASurveyMeter TechnicalManual
Ludlum Measurements, Inc. July 2020
Meter Compensation 7-2
Fast/Slow Time Constant 7-2
Low Voltage Supply 7-2
Low Voltage Reference 7-2
High Voltage Supply 7-3
Alarm 7-3
Recycling 8
Radiation Basics 9
Radiation and Life 9-1
The Unstable Atom 9-2
Radioactive Decay 9-3
Ionizing Radiation 9-4
Measuring Ionizing Radiation 9-5
What are the Health Risks from Ionizing Radiation? 9-6
How Much Ionizing Radiation is Dangerous? 9-7
Background Radiation 9-10
Man-made Radiation 9-11
Protection from Radiation 9-11
Standards and Regulation 9-12
Who is in Charge? 9-12
Troubleshooting 10
Troubleshooting Electronics that utilize a Scintillation Detector 10-1
Troubleshooting Scintillators 10-3
Parts List 11
Model 12SA Survey Meter 11-1
Main Board, Drawing 464 x 649 11-1
Calibration Board, Drawing 363 × 665 11-4
Wiring Diagram, Drawing 464 × 56 11-4
Drawings and Diagrams 12

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Ludlum Measurements, Inc. Page 1-1 July 2020
Introduction
he Ludlum Model 12SA Survey Meter is a portable gamma survey
instrument with adjustable audio and visual alarms. The instrument
utilizes an internally mounted 2.5 x 2.5 cm (1 x 1 in.) sodium iodide
[NaI(T1)] scintillator, which offers optimum performance in
locating and measuring low levels (near “background”) of gamma radiation.
The unit features range multipliers of ×1, ×10, ×100, and ×1000, which
provide an overall range of 0-3000 microroentgens per hour (µR/hr) when
used in conjunction with a 0-3 µR/hr meter dial (others are available). Other
features include a two-position meter response time switch, adjustable
detector operating voltage (HV), and an audio ON/OFF switch.
The instrument is capable of using either standard ˝D˝cell flashlight
batteries or nickel-cadmium rechargeable batteries. However, the Model
12SA does not include circuitry for recharging the batteries. The two ˝D˝ cell
batteries are located in an isolated compartment, easily accessible from the
front panel.
Section
1
T

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Ludlum Measurements, Inc. Page 2-1 July 2020
Getting Started
Unpacking and Repacking
Remove the calibration certificate and place it in a secure location. Remove
the instrument and accessories (batteries, cable, etc.) and ensure that all of
the items listed on the packing list are in the carton. Check individual item
serial numbers and ensure calibration certificates match. The Model 12SA
serial number is located on the front panel below the battery compartment.
To return an instrument for repair or calibration, provide sufficient packing
material to prevent damage during shipment. Also provide appropriate
warning labels to ensure careful handling.
Every returned instrument must be accompanied by an Instrument Return
Form, which can be downloaded from the Ludlum website at
www.ludlums.com. Find the form by clicking on the “Support” tab and
selecting “Repair and Calibration” from the drop-down menu. Then choose
the appropriate Repair and Calibration division where you will find a link to
the form.
Battery Installation
Ensure the Model 12SA range selector switch is in the OFF position. Open
the battery lid by pushing down and turning the quarter-turn thumbscrew
counterclockwise a quarter of a turn. Install two ˝D˝ size batteries in the
compartment. Note the (+) and (-) marks inside the battery door. Match the
battery polarity to these marks. Close the battery box lid, push down, and
turn the quarter-turn thumb screw clockwise a quarter of a turn.
Note:
The center post of a flashlight battery is positive. The batteries
are placed in the battery compartment in opposite directions.
Section
2

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Ludlum Measurements, Inc. Page 2-2 July 2020
Battery Test
The batteries should be checked each time the instrument is turned on.
Move the range selector switch to the BAT position. Ensure that the meter
needle deflects to the battery check portion on the meter scale. If the meter
does not respond, check to see if the batteries have been correctly installed.
Replace the batteries if necessary.
Operational Check
Ensure that both toggle switches (AUD ON/OFF and F/S) are in the up (ON
and F) position.
Note:
Operation of this instrument with the toggle switches in the
down (OFF and S) position is not recommended for surveys.
These positions should be used for specific measurements in a
radiation field or “hot spot.”
Turn the range selector switch to the BAT position. The meter needle should
fall within the BAT OK or BAT TEST marks on the meter face. Replace the
batteries if needed.
Turn the range selector switch to the ×10 position. If no source of radiation
is nearby, any meter deflection should be due to background radiation. At
Ludlum Measurements, a typical background reading is 6-12 µR/hr (0.06-
0.12 µSv/h).
Expose the instrument to a check source with the source oriented with the
center of the crystal (identified by the intersection of the indentations on the
instrument can), and verify that the instrument indicates within 20% of the
check source reading obtained during the last calibration.
Note:
To aid in consistent check source readings between
operational checks, orientate the source to the instrument
crystal in identical fashion for each check.

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Audible beeps should be heard with increasing frequency as the source is
brought closer to the detector, and as the meter needle deflects upscale.
Ensure that the ALARM lamp and constant audible tone are activated when
the check source is positioned to where the meter needle deflects above the
alarm threshold.
The AUD ON/OFF switch will silence the audible clicks if in the OFF position.
It is recommended that the AUD ON/OFF switch be kept in the OFF position
when not needed in order to preserve battery life.
Note:
Operation of this instrument with the AUD ON/OFF switch in
the down (OFF) position is not recommended for surveys. This
position should be used for specific measurements in a
radiation field or “hot spot.”
Increase the source activity for a measurement of 10-100 µR/hr. While
observing the meter fluctuations, select between the fast and slow response
time (F/S) positions to observe variations in the display. The ˝S˝position
should respond approximately five times slower than the ˝F ˝position.
Note:
The slow response position is normally used when the
instrument is displaying low numbers, which require a more
stable meter movement. This position is not recommended for
surveys. The fast response position is used at high rate levels.
Check the meter reset function by depressing the RESET pushbutton and by
ensuring the meter needle drops to˝0˝.
Proceed to use the instrument.
Surveying for Radiation
BACKGROUND AND MAN-MADE RADIATION
Naturally occurring background radiation is the main source of radiation
exposure for most people. The amount of naturally occurring background
radiation is dependant upon geographical location, environmental factors,