Ludlum Measurements 3A User manual

LUDLUM MODEL 3A
SURVEY METER
June 2020
Serial No. 336641 and Succeeding
Serial Numbers

LUDLUM MODEL 3A
SURVEY METER
June 2020
Serial No. 336641 and Succeeding
Serial Numbers

Model 3A Survey Meter
page i
STATEMENT OF WARRANTY
Ludlum Measurements, Inc. warrants the products covered in thismanual 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,
notifyLudlum 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.
Therearenowarranties,expressor implied,including withoutlimitationanyimplied
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
remedyshallberepair orreplacement, attheoption ofLudlumMeasurements. Inno
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
sendtotheaddressbelow. Allshipmentsshouldincludedocumentationcontainingreturnshipping
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]

Model 3A Survey Meter
page ii
TABLE OF CONTENTS
1. GENERAL.................................................................................................................................................................1
2. SPECIFICATIONS.....................................................................................................................................................1
3. DESCRIPTION OF CONTROLS AND FUNCTIONS......................................................................................................1
4. OPERATING PROCEDURES ......................................................................................................................................2
5. CALIBRATION .........................................................................................................................................................2
5.1 Calibrating CPS Scale .......................................................................................................................................2
5.2 Detector Operating Point ................................................................................................................................2
5.3 Alarm Circuit....................................................................................................................................................3
6. MAINTENANCE ......................................................................................................................................................3
7. PARTS LIST.............................................................................................................................................................4
Model 3A Survey Meter..........................................................................................................................................4
Main Circuit Board, Drawing 464 x 639...........................................................................................................4
Calibration Board, Drawing 363 x 650.............................................................................................................5
Wiring Diagram, Drawing 363 x 653................................................................................................................5
DRAWINGS AND DIAGRAMS..........................................................................................................................................7

Model 3A Survey Meter
page iii

Model 3A Survey Meter
page 1
1. GENERAL
The Model 3A Survey Meter is a portable
radiographic survey instrument with the additional
feature of an audible and visual alarm. The alarm
circuit is adjustable from a meter scale deflection of
0 to above full scale for each range multiple. The
meter scale presentation is 0-50 counts per second
(cps) with a total range of 0-5000 cps.
The unit body is made of cast aluminum, including
the meter housing. Other operating features of the
instrument include a unimorph speaker mounted to
the instrument can with an audioON-OFF capability,
fast-slow meter response, meter reset button,anda
six-position switch for selecting battery check or
scale multiples of X0.1, X1, X10, and X100. Each
range multiplier has its own calibration poten-
tiometer.
Any GM probe offered by the company will operate
on this unit as well as many of the scintillation
detectors. The instrument is set for 900-volt, GM
tube operation. For special requirements, it may be
adjusted for operation with any GM or scintillator
tube between 400 and 1500 volts.
The unit is operated with batteriesforoperationfrom
-20 to 50 °C (-4 to 122 °F). For temperature
operation to -40 to 65 °C (-40 to 150 oF), either very
fresh alkaline batteries or rechargeable NiCd
batteries may be used. Battery drain averages 30
milliamperes.
2. SPECIFICATIONS
POWER: two standard "D" size batteries
FOUR LINEAR RANGES: from 0 to 5000 counts
per second (CPS); meter scale presentation is 0 to
50 CPS with range multipliers of X0.1, X1, Xl0, and
X100
THRESHOLD: 40 ±10 mV
AUDIO: built-in unimorph speaker with an ON-OFF
switch
HIGH VOLTAGE: externally adjustable from 400 to
1500 volts
RESPONSE: 4 or 22 seconds, 10-90% of final
reading
LINEARITY: ±10% of true value
ALARM INDICATION: audible and visual indication
when above alarm threshold
ALARM RANGE: 0 to off-scale for each range
multiple; latching alarm
BATTERY DEPENDENCE: Instrument calibration
changes less than 3% withinbattery check limits on
meter.
METER: 1 milliampere, pivot-and-jewelsuspension,
6.4 cm (2.5 in.) scale
CONNECTOR: series "C", 706 U/G; BNC or MHV
may also be provided
SIZE: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x
W x L), including handle
WEIGHT: 1.6 kg (3.5 lb), including batteries
FINISH: drawn-and-cast aluminum powder-coat
paint.
3. DESCRIPTION OF CONTROLS AND FUNCTIONS
Range Multiplier Selector Switch: A six-position
switch marked OFF, BAT, X100, X10, X1,and X0.1.
Turning the range selector switch from OFF to BAT
position provides operator a battery check of the
instrument. A BAT check scale on the meter
provides a visual means of checking the battery
status. Moving the range selector switch to one of
the range multiplier positions (X0.1, X1, X10, X100)
provides the operator with an overall range of
0-5000 cps. Multiply the scale reading by the
multiplier for determining the actual reading.
AUDIO ON-OFF Toggle Switch: In the ON position
the switch 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.

Model 3A Survey Meter
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F-S Toggle Switch: Provides meter response.
Selecting the “F”position of the toggle switch
provides 10-90% of final meter reading in 4
seconds. In "S" position, 10-90% of final meter
reading 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.
RESET Pushbutton Switch:Whendepressed,this
switch provides a rapid means to drive the meter to
zero and reset the alarm.
High Voltage Adjustment: provides a means to
vary the high voltage from 400 to 1500 volts. The
high-voltage setting may be checked at the
connector with an appropriate voltmeter.
Range Calibration Adjustments: 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.
ALARM Light: a red lamp that comes on to give
visual alarm when radiation is above the alarm
threshold
Alarm SET: a screwdriver adjustment to set the
threshold for the alarm circuit. The threshold is set
by desired needle displacement on the meter scale.
The range is adjustable from 10% to off-scale on
each range multiple.
4. OPERATING PROCEDURES
Note: To open the Battery lid, twist the lid button
counterclockwise 1/4 turn. To close, twist
clockwise 1/4 turn.
Open the lid and install two "D" size
batteries. Note (+) (-) marks on the inside of
the lid. Match the battery polarity to these
marks.
Note: The enter post of the battery is positive.
Close the battery box lid.
Switch the range switch to BAT. The meter
should deflect to the battery check portion
of the meter scale. If the meter does not
respond, recheck that the batteries have
proper polarity.
Connect the cable to the instrument and
detector.
Turn the instrument range switch to X100.
Expose the detector to a check source. The
speaker should click with the AUDIO ON-
OFF switched to ON. If the alarm circuit
energizes, move the source away from the
detector and push the reset button.
Move the range switch to the lower scales
until a meter reading is indicated. The
toggle switch labeled F-S should have fast
response in “F” and slow response in "S".
Keep the source at a distance from the
detector that will keep the alarm circuit from
energizing.
Depress the RESET switch. The meter
should zero and the audio/visual alarm
should turn off.
Check calibration and proceed to use the
instrument.
5. CALIBRATION
5.1 Calibrating CPS Scale
To calibrate the CPS scale, aLudlum Model
500 Pulser generator or equivalent is
required.
Adjust the ALARM SET control fully
counterclockwise to keep the alarm circuit
from tripping during scale calibration.
Connect the pulse generator to the
instrument and adjust the pulse frequency
to provide 4/5-scale deflection on the X100
range (4,000 cps). Adjust the X100 range
calibration potentiometer as required.
Decrease the pulser frequency bydecades
and adjust each range calibration
potentiometer accordingly.
5.2 Detector Operating Point
For scintillation detectors, adjust the HV for
plateau operations. Expose the unit to asource
and develop an operating voltage-versus-count

Model 3A Survey Meter
page 3
rate-plot on semi-log paper. Set the operating
voltage at the flattest position of the curve near
the knee of the curve.
For GM detectors, adjust the HV to 900 volts.
For special applications, the power supply may
be adjusted from 400 to 1500 volts.
Note: Measure high voltage withaModel500 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. Do not use a vacuum tube type
voltmeter for this adjustment unless an external,
high-voltage multiplier probe is used.
5.3 Alarm Circuit
After HV and range controls are set, the alarm set
control may be adjusted to the desired alarm
threshold. Minimum setting is 10% of the meter
scale; maximum setting is full-scale deflection.
When the alarm circuit is energized, both the audio
and visual indications should occur. Pushing the
reset button resets the meter and alarm circuit.
6. MAINTENANCE
Instrument maintenance consists of keeping the
instrument clean and periodically checking the
batteries and the calibration.
To assure proper operation of the instrument
between calibrations, the instrument should be
tested with a check source prior to each use. A
reference readingshouldbeobtainedwhenexposed
to the check source in a constant and reproducible
manner at the time of calibration. If the instrument
response differs from the reference readingbymore
than ±20%, the instrument should be returned to a
calibration facility for maintenance, repair, or
recalibration as required.
Recalibration should be accomplished after any
maintenance or adjustment of any kind has been
performed on the instrument. Batteryreplacements
are not considered to be maintenance, and do not
normally require the instrument to be recalibrated.
Ludlum Measurementsrecommendsrecalibrationat
intervals no greater than one year. Check the
appropriate regulatory agency’s regulations to
determine required recalibration intervals.
The batteries should be removed and the battery
contacts cleaned of any corrosion at least every
three months. If the instrument has beenexposed to
a very dusty or corrosive atmosphere, service
batteries more frequently.
Use a spanner wrench to unscrew the battery
contact insulators, exposing the internal contacts
and battery springs. Removing the handle will
facilitate access to these contacts.
Note: Never store the instrument over
30 days without removing batteries.
Although this instrument willoperateat
very high ambient temperatures,
battery seal failure can occur at
temperatures as low as38˚C (100 ˚F).

Model 3A Survey Meter
page 4
7. PARTS LIST
Ref. No. Description PartNo.
Model 3A Survey Meter
UNIT Completely Assembled
Model 3A Survey Meter 48-1408
Main Board, Drawing 464 X 639
BOARD Assembled Circuit 5464-639
CAPACITORS
C38 0.0015μF, 3kV, C 04-5518
C40-C41 0.0015μF, 3kV, C 04-5518
C42 0.0027μF, 3kV, C 04-5520
C50 100pF, 3kV 04-5532
C56 100μF, 10V, DT 04-5576
C57 100pF, 3kV 04-5532
C102 100μF, 10V, DT 04-5576
C103 10μF, 20V, DT 04-5592
C104 47μF, 16V, DT 04-5550
C105 10μF, 20V, DT 04-5592
C106 0.001μF, 100V, C 04-5519
C109 0.01μF, 100V 04-5523
C112 470pF, 100V, C 04-5555
C113 0.01μF, 100V 04-5523
C115 100μF, 10V, DT 04-5576
C117 100pf, 100v, C 04-5527
C119 0.001μF, 100V, C 04-5519
C121 330pF, 100V 04-5531
C126 10μF, 20V, DT 04-5592
C134 100μF, 10V, DT 04-5576
C163 0.01μF, 100V 04-5523
C170 0.1μF, 100V, C 04-5521
C171 1μF, 35V, DT 04-5575
C191 0.0015μF, 3kV, C 04-5518
C199 0.01μF, 100V 04-5523
TRANSISTORS
Q6 2N3904G 05-5755
Q15 MPSW51AG 05-5765
Q44 2N3904G 05-5755
Q96 2N3904G 05-5755
Q145 2N4402BU 05-5763
Q200 2N4402BU 05-5763
Q201 2N7000 05-5820
Q213 2N3904G 05-5755
INTEGRATED CIRCUITS
U1 CMXT3904TRLF 05-5888
Ref. No. Description Part No.
U2 TLC372 06-6265
U3 CD4098 06-6066
U4 CMXT3906TRLF 05-5890
U5 ICM7555 06-6136
U6 TLC27M7IP 06-6248
U7 MAX631 06-6249
U8 CMXT3906TRLF 05-5890
U9-U11 CMXT3904TRLF 05-5888
U101 LM385Z-1.2 05-5808
DIODES
CR94 1N4148 07-6272
CR166-CR167 1N4007 07-6274
CR169 1N4007 07-6274
CR175 1N4007 07-6274
CR202 1N4148 07-6272
CR207 1N4148 07-6272
RESISTORS
R18 1k 10-7009
R27 33k 10-7019
R36 10M 10-7031
R46 10k 10-7016
R47 1G 12-7686
R63 82k 10-7022
R64 1k 10-7009
R65 10k 10-7016
R66 1k 10-7009
R68 8.2k 10-7015
R70 4.7k 10-7014
R72 33k 10-7019
R74 180k 10-7068
R75 33k 10-7019
R76 100 OHM 10-7004
R77 2.2k 10-7012
R78 22k 10-7070
R79 100k 10-7023
R81 10k 10-7016
R83 100k 10-7023
R84 470k 10-7026
R86 2.7M 10-7029
R87 10k 10-7016
R89 100k 10-7023
R91 4.7k 10-7014
R128 100k 10-7023
R137 10k 10-7016
R138 1M 10-7028
R147 715K 12-7645
R150 2.37k 12-7648
R159 10k 10-7016
R172 47k 10-7020

Model 3A Survey Meter
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Ref. No. Description Part No.
R177 200 OHM 10-7006
R189 301 OHM 12-7855
R196 10k 10-7016
R203 22k 10-7070
R204-R205 100k 10-7023
R206 22k 10-7070
R208-R210 100k 10-7023
R211 1M 10-7028
THERMISTORS
RT181 150 OHM 07-6332
RT190 150 OHM 07-6332
TRANSFORMERS
T165 L8050 40-0902
INDUCTORS
L13 470uH 21-9600
MISCELLANEOUS
P1 1-640456-5 13-8355
P2 640456-2 13-8073
W2-28 Cloverleaf 18-8771
Calibration Board, Drawing 363 x 650
BOARDAssembled Calibration 5363-811
CAPACITORS
C1 0.047μF, 100V, C 04-5565
C2 0.0047μF, 100V, C 04-5570
RESISTORS
R1-R3 1M Trimmer 09-6814
R4-R6 100k Trimmer 09-6813
R7 100k 10-7023
RESISTOR NETWORK
RN1 10k SIP 8P 12-7720
MISCELLANEOUS
P3 640456-5 MTA100 13-8057
P4 640456-4 MTA100 13-8088
Ref. No. Description Part No.
Wiring Diagram, Drawing 363 x 653
AUDIO
DS1 UNIMORPH #6030 21-9251
CONNECTORS
J1 1-640442-5 MTA100 13-8383
J2 640442-2 MTA100 13-8178
J3 640442-5 MTA100 13-8140
J4 640442-4 MTA100 13-8170
J5 RECPT-UG706/U
SCREW-IN "C" 13-7751
SWITCHES
S1 PA-600-210 08-6501
S2-S3 7101-SYZ-QE 08-6511
S4 30-1-PB GRAYHIL 08-6517
BATTERY
B1-B2 DURACELL "D" 21-9313
MISCELLANEOUS
DS1 BULB #338 21-9307
* LAMP HOLDER
101-8430-09-201 21-9410
* RED LENS 140-1471 21-9411
M1 PORT BEZEL
W/MOVEMENT 4363-188
* METER BEZEL W/GLASS
W/O SCREWS 4363-352
* METER MOVEMENT
(1mA) 15-8030
* PORTABLE METER
FACE 7363-136
* PORTABLE BATTERY NEGATIVE
CONTACT ASSY. 2001-065
* PORTABLE BATTERY POSITIVE
* CONTACT ASSY. 2001-066
PORTABLE CAN ASSY 4363-441
* PORT. CAL COVER
W/SCREWS 4363-200
* PORT KNOB CASTOM 08-6613
PORTABLE BATTERY LID WITH
STAINLESS CONTACT 2009-036
* PORTABLE BATTERY LID X100
7363-190
* PORT LATCH KIT
W/O BAT LID 4363-349
* MAIN HARNESS
Model 2A/3A 8363-827

Model 3A Survey Meter
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Ref. No. Description Part No.
* HARNESS-PORT
CAN WIRES 8363-462
* PORT HANDLE (ROLLED)
W/SCREWS 4363-139
* PORT HANDLE FOR CLIP
W/SCREWS 7363-203
* REPLACEMENT CABLE
(STD 1 m [39 in.]) 40-1004
* CLIP (44-3 TYPE)
W/SCREWS 4002-026-01
* CLIP (44-7 TYPE)
W/SCREWS 4010-007-01
* CLIP (44-6 TYPE)
W/SCREWS 4010-008-01

Model 3A Survey Meter
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DRAWINGS AND DIAGRAMS
Main Circuit Board, Drawing No. 464 x 639
Main Circuit Board Component Layout, Drawing 464 x 642 (2 sheets)
Calibration Board, Drawing No. 363 x 650
Calibration Board Component Layout, Drawing 363 x 651
Wiring Diagram, Drawing No. 363 x 653