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)

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The dial shown below has three arcs: a counts per minute scale (cpm), a
linear mR/hr scale, and a non-linear mR/hr scale for the ×100 range
only. The meter face also has a BAT TEST position.
The top cpm scale is valid for the ×0.1, ×1, ×10, and the ×100 ranges. The
linear (middle) mR/hr scale is valid for the ×0.1, ×1, and ×10 ranges. The
non-linear mR/hr scale is valid for the ×100 range only. This meter face is
commonly referred to as a “combo” meter face since it has both count rate
(cpm) and exposure rate (mR/hr) arcs. Simpler meter faces may only have
a count rate or an exposure rate arc(s) like the previous meter faces shown.
A “combo” meter face is specifically designed for a particular detector. In
the example above, the 1.0 mR/hr mark on the middle arc lines up with
3.3 kcpm on the upper arc. The meter face in this example works with a
detector that receives 3.3 kcpm per mR/hr (the Ludlum Model 44-9
pancake detector.)
In the following picture, the needle is on the first tick mark past the 4
kcpm mark. Therefore, if the instrument selector switch is on the ×0.1
range, the reading is 4.2 kcpm (multiplied by) ×0.1 = 420 cpm.

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The same needle indications on successive ranges would be:
×1 = 4.2 kcpm (or 4,200 cpm)
×10 = 42 kcpm (or 42,000 cpm)
×100 = 420 kcpm (or 420,000 cpm)
If you use the mR/hr scales, then the readings would be:
×0.1 = 0.13 mR/hr
×1 = 1.3 mR/hr
×10 = 13 mR/hr
×100 = 180 mR/hr*
Note:
*This reading is using the bottom (non-linear) scale.
Many different dials are available, but each can be used as described above.
Operational Check
To assure proper operation of the instrument and detector(s) between
calibrations, an instrument operational check including battery test and
instrument test (as described above) should be performed at least daily or prior
to use, whichever is less frequent. A reference reading(s) with a check source
should be obtained with the detector(s) in a constant and reproducible manner
at the time of calibration or at the time the instrument is received in the field.
If at anytime the instrument fails to read within 20% of the reference reading
when using the same check source, it should be sent to a calibration facility for
recalibration and/or repair. If desired, multiple readings may be taken at
different distances and/or with different sources so that other ranges or scales
are checked.

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Specifications
0
Multipliers: ×1, ×10, ×100, and ×1000 selected by a front-panel range
selector switch
High Voltage: adjustable from 400 to 2500 volts; can be read on the
meter; electronically regulated to 1%; support of scintillation loads to
1500 volts, proportional loads to 2500 volts
Input Sensitivity: adjustable from -1 to -100 mV
Input Impedance: 0.1 megohm
Meter: 6.4 cm (2.5 in.) arc, 1 mA analog type
Meter Dial: 0-500 cpm, 0-2.5 kV, BAT TEST (others available)
Range: typically 0-500,000 counts/minute (CPM)
Linearity: reading within 10% of true value with detector connected
Calibration Controls: individual potentiometers for each range;
accessible from the front cover while in operational status
Response: toggle switch for FAST (4 seconds) or SLOW (22 seconds)
from 10% to 90% of final reading
Connector: Series ˝C˝(other available)
Cable: 39-inch with ˝C˝connector
Reset: pushbutton to zero the meter
Audio: built-in unimorph speaker with ON-OFF switch (greater than
60 dB at 0.61 m {2 ft})
Section
3

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Power: two ˝D˝cell batteries housed in a sealed externally accessible
compartment
Battery Dependence: instrument calibration change less than 3%
within battery check limits on the meter
Battery Life: typically 2000 hours with alkaline batteries (battery
condition may be checked on the meter)
End-of-Battery Life Warning: At 2.1 Vdc, the meter needle will drop to
the edge of the BAT TEST or BAT OK area when the meter selector switch
is moved to the BAT position. At 2.0 Vdc, a steady audible tone will be
emitted to warn the user of the low-battery condition.
Size: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 inch) (H x W x L)
Weight: 1.6 kg (3.5 lb) including batteries.
Construction: cast-and-drawn aluminum with beige powder coating

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Ludlum Measurements, Inc. Page 4-1 July 2017
Identification of Controls and
Functions
See the Model 12 front-panel drawing at the
beginning of this manual to reference the
following controls:
(A) Meter: 6.4 cm (2.5 in.) arc, 1 mA analog type with pivot-and-jewel
suspension. Typical meter dials are 0-0.2 mR/hr, 0-2.0 µSv/h, 0-500
cpm or combination of exposure rates (0-0.2 mR/hr or 0-2.0 µSv/h),
and cpm and BAT TEST.
(B) Connector: Used to connect the detector to the instrument.
Typically series ˝C˝but can be ˝BNC,˝˝MHV,˝˝UHF˝or others.
(C) Range Selector Switch: A six-position switch marked OFF, BAT,
×1000, ×100, ×10, and ×1. Turning the range selector switch from OFF
to BAT provides the operator with a battery check of the instrument. A
BAT check scale on the meter provides a visual means of checking the
battery-charge status. Moving the range selector switch to one of the
range multiplier positions (×1000, ×100, ×10, ×1) provides the operator
with four decades of an overall range. Multiply the scale reading by the
multiplier to determine the actual scale reading.
(D) Discriminator Adjustment: allows the input sensitivity to be
adjusted from 1 to 100 millivolts (mV).
(D) HV Adjustment: provides a means of varying the high voltage (HV)
from 400 to 2500 volts.
(D) Range Calibration Adjustment: recessed potentiometers located
under the calibration cover, on the right side of the front panel. These
adjustment controls allow individual calibration for each range
multiplier.
(E) Battery Compartment: sealed compartment to house two ˝D˝cell
batteries.
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(F) RES Pushbutton Switch: when depressed, this switch provides a
rapid means of driving the meter needle to zero.
(G) AUD ON-OFF Toggle Switch: In the ON position, this operates the
unimorph speaker, located on the left side of the instrument. The
frequency of the clicks is relative to the rate of the incoming pulses. The
higher the rate, the higher the audio frequency. The audio should be
turned OFF when not required to reduce battery drain.
Note:
A low-battery condition results in a steady audio tone,
regardless of the position of the AUD ON/OFF switch.
(H) F-S Toggle Switch: Provides meter response. Selecting the fast, ˝F˝
position, of the toggle switch provides 90% of full-scale meter deflection
in four seconds. In the slow, ˝S˝position, 90% of full-scale meter
deflection takes 22 seconds. In the ˝F˝position there is fast response and
large meter deviation. The ˝S˝position should be used for slow response
and damped meter deviation.
Note:
The slow response position is normally used when the
instrument is displaying low numbers, which require a more
stable meter movement. The fast response position is used at
high rate levels.
(I) HV Pushbutton Switch: When depressed, displays the detector high
voltage on the meter. The output resistance of the HV supply is 1.5
megohms with a typical scintillation voltage divider of 100 megohms.
The actual detector voltage will be 98.5% of the indicated voltage.

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Safety Considerations
Environmental Conditions for Normal Use
The detector may be affected by altitude. Refer to the detector manual
for more information.
Indoor or outdoor use
No maximum altitude
Temperature range of -20 to 50 °C (-4 to 122 °F); may be certified for
operation from -40 to 65 °C (-40 to 150 °F)
Maximum relative humidity of less then 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.
Section
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The Model 12 Survey Meter is marked with the
following symbols:
CAUTION, RISK OF ELECTRIC SHOCK (per ISO 3864, No. B.3.6)
–designates a terminal (connector) that allows connection to a voltage
exceeding 1 kV. Contact with the subject connector while the instrument is
on or shortly after turning off may result in electric shock. This symbol
appears on the front panel.
CAUTION (per ISO 3864, No. B.3.1) –designates hazardous live voltage
and risk of electric shock. During normal use, internal components are
hazardous live. This instrument must be isolated or disconnected from the
hazardous live voltage before accessing the internal components. This
symbol appears on the front panel. Note the following precautions:
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 sit for one minute before accessing
internal components.
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 9, “Recycling,” for further information.
The “CE” mark is used to identify this instrument as being acceptable for
use within the European Union. It is located on the battery lid.
Cleaning and Maintenance Precautions
The Model 12 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.

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Calibration and Maintenance
Calibration
Calibration controls are located on the front of the instrument under the
calibration cover. The controls may be adjusted with a 1/8-inch blade
screwdriver.
Note:
Local procedures may supersede the following
The instrument may be calibrated to true reading or, when used with a
single source, geometry calibration may be used. Both methods are
described below. Unless otherwise specified, the instrument is calibrated
to true reading at the factory.
Note:
Measure high voltage with a Model 500 Pulser or a high-
impedance voltmeter with a high-meg probe. If one of
these instruments is not available, use a voltmeter with a
minimum of 1000 megohm input resistance.
True Reading Calibration
Connect the input of the instrument to a negative pulse generator, such
as a Ludlum Model 500 Pulser.
Caution!
The instrument input operates at a high potential.
Connect the pulse generator through a 0.01µF, 3000-volt
capacitor, unless the pulse generator is already protected.
Section
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Adjust the pulser frequency to correspond to the 3/4-scale value of the
instrument. Increase the Pulser output voltage until the pulse height is twice
the input sensitivity. Adjust the calibration potentiometer for a 3/4-scale
reading. Repeat for each range.
To correlate this calibration to a detected radiation value, the probe
efficiency must be determined. Select the operating point for the probe used
as outlined in the following section. Then determine the count rate with the
probe exposed to a calibration source. The ratio of the instrument count rate
versus the known source value is the probe efficiency. This degree will be
different for various types of probes and sources. By using probe efficiency,
one determines the actual emission rate of an unknown source.
Note:
For proportional and scintillation detectors, changes in the HV
and DIS controls will change the apparent detector efficiency
for many sources.
Geometry calibration is often used when the instrument is utilized to
measure radiation with a limited spectrum; for example, a single isotope
calibration. To calibrate the instrument using this technique, obtain
calibration sources with a spectrum similar to the target radiation. Expose
the probe to the source and adjust the calibration control until the meter
reading corresponds to the source value. Repeat this procedure with scaled
sources for each instrument range.
In the event that only one source is available, calibrate the corresponding
range to that source. Disconnect the probe and connect a pulse generator to
the instrument. Determine the pulse rate for 3/4-scale deflection on the
calibrated range. Using this reading as a reference, calibrate each succeeding
range by increasing (or decreasing) this rate by a factor of 10 for each.
Internal Calibration after Overhaul
Connect instrument to a Model 500 Pulser. Adjust the front-panel HV
adjustment for a pulser high-voltage meter reading of 1500 volts. Depress
the HV pushbutton while adjusting the main board HV SET potentiometer
(R38) for a Model 12 meter reading of 1500 volts.