Ludlum Measurements 12 User manual

LUDLUM MODEL 12
SURVEY METER
July 2017
Serial Number 218039 and Succeeding
Serial Numbers

LUDLUM MODEL 12
SURVEY METER
July 2017
Serial Number 218039 and Succeeding
Serial Numbers

Ludlum Measurements, Inc. July 2017
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 2017
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Connecting a Detector to the Instrument 2-2
Battery Test 2-2
Instrument Test 2-2
Reading the Meter Face Dial 2-3
Operational Check 2-6
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
Calibration and Maintenance 6
Calibration 6-1
True Reading Calibration 6-1
Internal Calibration after overhaul 6-2
Establishing an Operating Point 6-3
Maintenance 6-4
Recalibration 6-5
Batteries 6-5
Troubleshooting 7
Troubleshooting Electronics which utilize a
GM, Scintillator, or Proportional Detector 7-1
Troubleshooting GM Detectors 7-3

Model12 TechnicalManual
Ludlum Measurements, Inc. July 2017
Troubleshooting Scintillators 7-4
Troubleshooting Proportional Detectors 7-4
Technical Theory of Operation 8
Main Board (Drawing 464 × 275 3 sheets) 8-1
Input 8-1
Amplifier 8-1
Discriminator 8-1
Audio 8-1
Scale Ranging 8-2
Digital Analog Converter 8-2
Ratemeter Drive Circuit 8-2
HV Meter Drive 8-2
Battery Test 8-2
HV Power Supply Board (Drawing 464 × 243) 8-3
Switching Convertor 8-3
Feedback 8-3
Voltage Control 8-3
Filtering 8-3
Recycling 9
Parts List 10
Model 12 Survey Meter 10-1
Main Board, Drawing 464 × 275 10-1
HV Power Supply Board, Drawing 464 × 243 10-4
Wiring Diagram, Drawing 464 × 309 10-5
Drawings and Diagrams 11

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Ludlum Measurements, Inc. Page 1-1 July 2017
Introduction
he Model 12 is a portable survey meter with four linear ranges used
in combination with exposure rate or CPM meter dials. The
instrument features a regulated high-voltage power supply,
unimorph speaker with audio ON-OFF capability, fast-slow meter
response, meter reset button, and a six-position switch for selecting battery
check or range multiples of ×1, ×10, ×100, and ×1000. Each range
multiplier has its own calibration potentiometer. The unit body and meter
housing are made of cast aluminum, and the can is 0.23 cm (0.09 in.) thick
aluminum.
The audio provides a brief “click” for every radiation event detected. It also
provides a steady tone to warn the user of a low-battery condition. This low
battery warning overrides the position of the AUD ON-OFF switch.
With an adjustable detector voltage of 400-2500 volts and adjustable
discriminator of 1-100 millivolts, this unit can be operated with most
proportional, scintillation, or GM detectors. Scintillation detectors will
require voltage divider circuit resistance in excess of 50 megohms.
The unit is operated with two ˝D˝cell batteries for operation -20 to 50 °C (-4
to 122 °F). For instrument operation below 0 °C (32 °F), either very fresh
alkaline or rechargeable NiCd batteries should be used.
Section
1
T

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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 12 serial
number is located on the front panel below the battery compartment. Most
Ludlum Measurements, Inc. detectors have a label on the base or body of
the detector for model and serial number identification.
Important!
If multiple shipments are received, ensure that the detectors
and instruments are not interchanged. Each instrument is
calibrated to specific detectors, and therefore not
interchangeable.
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. Include detector(s) and related
cable(s) for calibration.
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 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 12 range selector switch is in the OFF position. Open the
battery lid by pushing down and turning the quarter-turn thumbscrew
Section
2

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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 “D” size battery is positive.
Connecting a Detector to the Instrument
Caution!
The detector operating voltage (HV) is supplied to the detector
via the detector input connector. A mild electric shock may
occur if you make contact with the center pin of the input
connector. Switch the Model 12 range selector switch to the
OFF position before connecting or disconnecting the cable or
detector.
Connect one end of a detector cable to the detector by firmly pushing the
connectors together while twisting clockwise a quarter of a turn. Repeat the
process in the same manner with the other end of the cable and the
instrument.
Battery Test
Check the batteries daily or prior to use, whichever is less frequent, to assure
proper operation of the instrument. Move the range multiplier 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.
Instrument Test
After checking the batteries, turn the instrument range switch to the ×1000
position. Place the AUD ON-OFF switch in the ON position. Expose the
detector to a check source. The instrument speaker should emit ˝clicks˝
relative to the rate of counts detected. The AUD ON/OFF switch will silence

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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.
The detector cable can be a source of problems. Test the detector cable by
bending and flexing either end of the cable and checking for an increase in the
rate of counts detected. Replace the cable if an increase in the rate of counts is
detected.
Check the meter reset function by depressing the RES pushbutton switch and
ensuring the meter needle drops to “0.”
Once this procedure has been completed, the instrument is ready for use.
Reading the Meter Face Dial
Reading the meter face is very important for consistent measurements. There
are, in general, three types of meter faces: 1) count rate (typically cpm [counts
per minute]); 2) exposure rate (typically mR/hr); and 3) “combo” (typically
cpm and mR/hr). The following examples are intended to help the user
interpret the correct reading.
The normal procedure is to turn the range selector switch to the highest range
and if no readings are seen on the meter, turn the selector switch down to the
lower scales until a reading is seen. The ranges on the instrument selector
switch are multipliers for the meter reading. A typical single scale (one arc)
meter face with a cpm (counts per minute) dial is shown below.
The count rate scale reads 0-5K COUNTS/MINUTE (kcpm or 1000’s of
counts per minute) and has BAT TEST on the dial.
If the needle is pointing as indicated below and the instrument range
selection switch is on the ×0.1 scale multiple, then the reading is 3.5 kcpm
(multiplied by) × 0.1 = 350 cpm.

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The same needle indications on successive ranges would be:
×1 = 3.5 kcpm (or 3500 cpm)
×10 = 35 kcpm (or 35,000 cpm)
×100 = 350 kcpm (or 350,000 cpm)
A typical dual scale (two arcs) meter face is shown below. The top scale
reads 0-2 mR/hr. The bottom scale also reads 0-2 mR/hr and is for ×100
scale only. The ×100 ONLY scale will work correctly when the multiplier
switch is in the ×100 range. The meter face also has a BAT TEST position
on the dial.
If the needle is pointing as indicated below and the range selection switch
is on the ×0.1 scale, then the reading is 0.1 mR/hr.
The same needle indications on successive ranges would be:
×1 = 1.0 mR/hr (or 1,000 µR/hr)
×10 = 10 mR/hr (or 10,000 µR/hr)
×100 = 70 mR/hr (or 70,000 µR/hr)