Ludlum Measurements 2241-3 User manual

LUDLUM MODEL 2241-3 & 2241-3i
SURVEY METER
January 2016
Serial Number 299171 and Succeeding
Serial Numbers

LUDLUM MODEL 2241-3 & 2241-3i
SURVEY METER
January 2016
Serial Number 299171 and Succeeding
Serial Numbers

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. January 2016
Table of Contents
Introduction 1
Information on Model 2241-3i 1-2
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Connecting a Detector 2-2
Operational Check 2-2
Specifications 3
Removable Switchboard Adjustable Parameters 3-2
Internal Detector Specifications for Model 2241-3i 3-4
Identification of Controls and Functions 4
Display 4-1
Display Status Definitions 4-1
Front Panel Controls 4-2
Front Panel Calibration Controls 4-3
Main Board Controls 4-4
Switch Board Controls 4-5
Safety Considerations 5
Environmental Conditions for Normal Use 5-1
Detector Connector 5-1
Warning Markings and Symbols 5-1
Maintenance 6
Operational Check 6-1
Recalibration 6-1
Batteries 6-3
Technical Principle of Operation 7
Main Board 7-1
Switch Board 7-2
Display Board 7-3

Model2241-3&3i TechnicalManual
Ludlum Measurements, Inc. January 2016
Instrument Setup & Calibration 8
Entering or Changing Switch Board Parameters 8-1
Loading Default Parameters 8-1
The Function Switch 8-2
Function Switch Position Descriptions and Variables 8-2
Calibration 8-7
General Detector Setup Information 8-8
Counts per minute (C/m) Calibration 8-9
R/hr Calibration 8-11
Determining CC and DTC 8-12
Software License Agreement 8-19
Recycling 9
Parts List 10
Model 2241-3 Survey Meter 10-1
Main Circuit Board, Drawing 408 × 285 10-1
Calibration Board, Drawing 408 × 98 10-3
Display Board, Drawing 408 × 259 10-4
Switch Board, Drawing 408 × 45 10-5
Chassis Wiring Diagram, Drawing 408 × 101 10-5
Drawings and Diagrams 11
RS-232 Output Formats - Appendix A A
Binary Output Format A-1
ASCII Output Format A-4

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Introduction
he Model 2241-3 is a portable microprocessor-based digital Scaler/
Ratemeter designed for use with scintillation, Geiger-Mueller (GM),
and proportional-type detectors for measurement of ionizing
radiation. Data is presented on a four-digit (six digits in the scaler
mode) Liquid Crystal Display (LCD) with moving decimal point. A toggle
switch labeled SCA/RATE selects the desired operating mode for the
instrument. A five-position switch labeled ˝OFF/DET 1/DET 2/DET 3/DET
4˝allows for a quick change of operating parameters when changing out
detectors.
Programmable display units (RATEMETER mode only) can be represented in
R/hr, Sv/h, cpm, or cps with multipliers of micro (µ) or milli (m) for R/hr
and Sv/h and kilo (k) for cpm or cps. The display units are auto-ranging,
enabling the readout to display a broad range of radiation levels. The display
also offers lower limit capability. For example, the display can be set to show
only values that are greater than or equal to1 µR/hr.
This instrument incorporates independent adjustable alarms for RATEMETER
and SCALER operating modes. The RATEMETER mode has two alarm
indicators. The first-level alarm is indicated by display of the word ˝ALERT˝
on the LCD. The second-level alarm is indicated by display of the word
˝ALARM˝and by the emitting of a continuous audible tone. The SCALER
alarm condition will also display the word ˝ALARM˝and produce the same
audible tone. Both audible alarms may be silenced (acknowledged) by
depressing the RESET switch. All alarms are concurrent.
Other features include: 1) Dead Time Correction (DTC) to compensate for
detector dead time; 2) audible click-per-event with programmable 1, 10, 100,
and 1000 divide-by; 3) LCD backlight with programmable ON time; 4)
programmable fixed or variable response time; and 5) count overflow visual
alarm, indicative of the counting circuitry nearing the maximum counting
capability.
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All of the features described above may be programmed manually using the
internal switch board or by computer through the RS-232 port. Four
different detector operating parameters may be stored in non-volatile
memory. The switch board can be removed after entering or changing
parameters to prevent tampering with setup parameters.
A regulated high-voltage power supply, four independent set-point controls
adjustable from 400 to 2500 volts, and adjustable discrimination levels, add
versatility to the instrument. This supports operation for a broad range of
detectors and connecting cable lengths. All of the calibration controls are
covered to prevent any inadvertent adjustment to the detector operating
parameters.
The instrument is powered by two standard ˝D˝cell batteries. The unit body
is made of cast-and-drawn aluminum with beige powder coating, which aids
in the decontamination of surfaces.
The Model 2241-3i is identical to the Model 2241-3 except for the
following:
The five-position selector switch located on the front panel has been
modified to provide for selection of an internal detector. When selected, the
INT position (formerly DET4) switches detector operation to an internal,
energy-compensated Geiger-Mueller detector. Appropriate wiring changes
to accommodate the internal detector have been made; however, physical
dimensions are the same as for a Model 2241-3.
A drawing of the front-panel of the 2241-3i is included at the beginning of
this manual. A wiring diagram for the instrument is included in the back of
the manual with the other drawings. The internal detector specifications can
be found at the end of Section 3 of this manual.

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Getting Started
Unpacking and Repacking
Remove the calibration certificates and place them in a secure location.
Remove the instrument, detectors, 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 2241-3 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 are 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 OFF/DET 1/DET 2/DET 3/DET 4 switch is in the OFF position.
Open the battery lid by turning the quarter-turn thumb screw counter-
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clockwise. 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.
Note:
The center post of “D” size battery is positive.
Connecting a Detector
Caution!
The detector operating voltage (HV) is supplied to the detector
by way of the input connector. A mild electric shock may
occur if contact is made with the center pin of the input
connector. Switch the Model 2241-3 to the OFF position
before connecting or disconnecting the cable or detector.
Connect a detector to the Model 2241-3 by using the cable provided; firmly
pushing the connectors together while twisting clockwise until the connector
latches (1/4 turn). The diagram to the left illustrates how this is done. Next,
place the detector selector switch in the appropriate position.
Operational Check
Place the SCA/RATE (scaler/ratemeter) switch in the RATE
position. Notice that the display goes through an initialization
sequence. The display will show all “8”s with decimal points.
Check to make sure all segments display, as illustrated in the
diagram to the left.
The LCD then displays the firmware number in the format
“P-XX YY.” The “XX” is the firmware number, and the “YY”
is the firmware version. (The figure to the left is for example
only; to illustrate location of display.)
The minimum displayable value (for example 00.0 µR/hr) should
be shown. When switched to the SCA position, a single “0” will
be displayed.

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The display will auto-range to the current level (see figure at left).
When auto-ranging down, the Model 2241-3 uses multiples of 5.
This technique keeps the decimal point from jumping between
numbers when viewing values around multiples of 10.
Check for a proper background reading:
If using a Ludlum Model 44-9 detector, a typical reading would be 25-50
cpm or 8-15 µR/hr.
If using a Ludlum Model 44-2 detector, a typical reading would be 1.4-2.6
kcpm or 8-15 µR/hr.
If using a Ludlum Model 133-7 detector, a typical reading would be 0 cpm
or 8-15 µR/hr.
A reference reading (or readings) 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 any time 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.
Switch the AUD ON/OFF switch to the ON position and confirm that the
external unimorph speaker produces an audible click for each event detected
(audio divide-by 1 parameter). The AUD ON/OFF switch will silence the
clicks if in the OFF position, however, an audible alarm condition will still be
heard.
Increase the source activity or lower the alert and alarm points to initiate an
ALERT and ALARM condition. (Refer to Section 8, Subsection “Entering or
Changing Switchboard Parameters.”) Depress the RESET switch to
acknowledge the audible alarm. Decrease the radiation activity below the
ALERT and ALARM threshold and depress the RESET switch to clear the alarm
conditions. If an alarm condition is not present, depressing the RESET switch
the first time will reset the alert condition and zero the ratemeter.
Position a check source to produce a ratemeter reading of 100 to 2000
counts per minute or 10-100 µR/hr. While observing the ratemeter
fluctuations, select between the fast and slow response time (F/S) positions
to observe variations in the display. The Sposition should respond

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approximately five times slower than the Fposition (for fixed response
mode) and three times slower when in variable response mode. The slow
response position is normally used when the Model 2241-3 is displaying low
numbers, which require a more stable display. The fast response position is
used at high count levels.
Place the SCA/RATE switch to the SCA position. Depress the COUNT switch
located in the end of the carrying handle in order to initiate a count cycle.
The word “COUNTING” should be flashing on the LCD during the count
cycle and should disappear at the end of the predetermined count time. If a
scaler ALARM condition occurs, the RESET switch can be depressed to
acknowledge the alarm; however, the COUNT switch must be depressed to
clear the visual ALARM and to restart the count cycle.
Depress and release the LIGHT switch. The backlight located behind the
LCD should illuminate (for pre-programmed ON time). Select the desired
F/S, AUD ON/OFF, and RATE/SCA parameters and proceed to use the
instrument.

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Specifications
0
Linearity: Readings are within 10% of true value with a detector connected.
Display: a four-digit Liquid Crystal Display (LCD) with digits 1.3 cm (0.5
in.) in height. Two additional 0.5 cm (0.2 in.) high digits are used for the
overflow counter (SCALER mode) and exponential powers (parameter setup).
Enunciators are provided for display units, ALERT, ALARM, low battery,
detector OVERLOAD (not used), counting OVERFLOW, and scaler COUNTING.
Warm-up Time: Unit may be used immediately after the LCD initialization
sequence is completed (approximately five seconds after power-up).
RATEMETER: Depending upon how the instrument was calibrated, the
RATEMETER can display in either R/hr, Sv/h, cpm, or cps when the control
switch is in the RATEMETER position.
SCALER: activated by pushbutton in handle when the three-position switch
is in the SCALER position. Count time is adjustable.
Calibration Controls: accessible from the front of the instrument
(protective cover provided). These controls are preset at the factory or
calibration lab and should not be adjusted by field personnel.
Discriminator / Input Sensitivity: adjustable from 2 to 100 mV;
negative pulse response
High Voltage: four independent controls, each adjustable from
400-2500 volts; four separate set points for each detector setup-
HV 1, HV 2, HV 3, and HV 4, regulated within 0.2% at 1000 Vdc;
maximum load of 50 µA.
RESET: a pushbutton for zeroing the display, acknowledging
and/or resetting the alarm.
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Note:
The RESET button only silences the alarm in the current mode
that the instrument is in. For example, the RESET button will
not affect the scaler alarm if the instrument is in the
ratemeter mode.
Light: display backlight activated by pushbutton
Audio: built-in audio speaker (unimorph) with AUD ON/OFF switch; at
maximum volume >60 dB at 2 feet; internal adjustable volume
Alert/Alarm: indicated by either an ALERT or ALARM enunciator on the
display (RATEMETER mode only) and by an audible tone
Power: two each, ˝D˝cell batteries housed in an externally accessible sealed
compartment. Current draw is approximately 35 mA with the backlight OFF.
Minimum battery voltage is 2.2 ±0.1 Vdc.
Battery Dependence: Meter readings vary by less than 3% from fully
charged batteries until the battery symbol appears, indicating the need for
recharge or replacement.
Battery Life: typically 200 hours with alkaline batteries (display indicates
low-battery condition). Instrument will operate for approximately 24 hours
after the battery symbol first appears.
Size: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x W x D)
Weight: 1.6 kg (3.5 lb), including batteries.
Removable Switchboard Adjustable Parameters:
Backlight ON Time: 5, 15, 30, 60, 90, 120, 180, or 240 seconds for the
backlight to stay on when activated by the pushbutton; factory set at 5.
Set Minimum Display: allows lower limit of the auto-ranging display to be
fixed. For example, the display can be set to only show values above or
equal to 1 µR/hr.

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RS-232 Data Dump Mode: enables or disables dump mode to the RS-232
port (˝D˝type connector). When enabled, the data will be dumped every
two seconds.
RS-232 Detector Setup Mode: allows for input of detector parameters via
the RS-232 port
Baud Rate: selects either 150, 300, 600, 1200, 2400, 4800, 9600, or 19200
bps
Detector Dead Time Compensation (DTC): adjustable from 0 to 9999
microseconds
Calibration Constant: adjustable from 0.001 to 280 × 109counts/display
unit
Display Units: can display in R/hr, Sv/h, cpm, or cps
Time Base: can display in seconds or minutes
Audio Divide: 1, 10, 100, or 1000 events per click
Response Time: variable or fixed ratemeter response (All stated times
correspond to a range of 10% to 90% of the final reading). Factory default
is variable so that the instrument will automatically adjust the response time
to the best setting for the current count rate.
Variable Response: dependent on the number of counts
present, typically 4 to 25 seconds for FAST, and 4 to 60 seconds
for SLOW
Fixed Response: The parameter is adjustable from 1-25
seconds resulting in a FAST response from approximately 2-50
seconds. The SLOW response is approximately 10-250 seconds.
For MDA-type measurements, the fixed response mode is
recommended.
Ratemeter Alert/Alarm: set at any point corresponding to the pre-selected
ratemeter range
Scaler Alarm: adjustable from 1 to 999999 counts
Scaler Count Time: adjustable from 1 to 9999 seconds

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Internal Detector Specifications for Model 2241-3i:
Operating Voltage: recommended 550 volts
Input Sensitivity: -30 mV ±10 mV
Dead Time: typically 80 microseconds
Energy Reponse: within ±15%
Tube: 30 mg/cm2 stainless steel (Halogen quench) GM
Size: 2.3 x 10.2 (0.9 x 4 in.) (Dia x L)
Temperature Range: -20 to 50 °C (-4 to 122 °F)

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Identification of Controls and
Functions
Display
The Model 2241-3 utilizes a four-digit liquid crystal display (LCD) with a
two-digit overflow (SCALER mode) and moving decimal point. The two
smaller digits located in the lower right corner of the display indicate
counter OVERFLOW when in the scaler counting mode (equivalent to a
six-digit scaler) or exponential power when in the parameter setup
mode. The upper right corner of the LCD displays units and
multiplier(s) - R/hr, mR/hr, or µR/hr; Sv/h, mSv/h or µSv/h; C/m,
kC/m, C/s or kC/s. The bottom part of the readout displays the
ALARM, ALERT, OFLOW, OVERLOAD (not used) enunciators and the
low-battery icon. COUNTING indicates that the scaler mode has been initiated
and is in the counting process.
Display Status Definitions
ALARM: Ratemeter or scaler count has increased above the preset alarm
threshold. An audible continuous tone will accompany the latching ALARM
condition. Depressing RESET will acknowledge the audible ratemeter and/or
scaler alarm. Depressing RESET a second time will reset the ratemeter
reading and ratemeter alarm. To reset the scaler ALARM, depress the COUNT
switch located in the carrying handle to re-initiate the scaler count cycle.
ALERT: Ratemeter count has increased above the preset alert threshold. To
reset an ALERT condition, press RESET once if in the non-alarm condition
and twice if in an alarm condition. (The first depression in the alarm
condition acknowledges the audible alarm.) The ratemeter will reset to the
minimum displayable reading each time the alert is reset.
OFLOW (Overflow) [RATEMETER mode]: Indicates that the incoming count
exceeds the capability to display stable or reliable readings corresponding to
the radiation level being measured. The overflow symbol will appear when
the ratemeter exceeds 100 kcps or if the dead time correction is greater than
75%. OFLOW will appear in the SCALER mode when the six-digit display
(four digits display and two overflow digits in right corner) reaches
“999999” and starts to roll over again.
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Low Battery icon: indicates that the batteries have decreased to the
minimum operating voltage of 2.2 ±0.1 Vdc. Instrument will continue to
operate for approximately 24 hours thereafter.
COUNTING: indicates that the scaler COUNT switch has been depressed and
that the scaler is accumulating counts for the pre-determined count time
Front Panel Controls
OFF/DET 1/DET 2/DET 3/DET 4Switch: a five-position rotary switch that
applies power to the instrument and selects the desired set of detector
parameters
SCA/RATE (Mode) Switch: a protected (locking) toggle switch that toggles
between ratemeter or scaler counting modes. The user pulls up and then
over to change modes.
AUD ON/OFF Switch: The click-per-event audio may be silenced or enabled
via this front-panel toggle switch. The audible alarm is independent of the
AUD ON/OFF switch and will override the audible click-per-event. An
audible alarm can only be silenced by depressing the RESET button.
F/S (Fast/Slow) Response Switch: a two-position toggle switch that selects
fast or slow counting response time
Variable Response: The Fposition allows the time constant (TC) to vary
from 1 to 10 seconds, while the Sposition varies from 1 to 30 seconds. The
response time is automatically adjusted in proportion to the incoming count
rate between the F/STC variables.
Fixed Response: The Fposition corresponds to the selected fixed response
time - TC. The Sposition is five times slower than the selected fast TC.
LIGHT (LCD Backlight): A pushbutton switch, when depressed, illuminates
the LCD for a pre-programmed time. The backlight ON time can be selected
between 5 and 240 seconds during the parameter setup.

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RESET Pushbutton: In the non-alarm condition, depressing the RESET
switch resets the ratemeter display to the minimum display readout. In an
alarm condition (ratemeter or scaler), depressing RESET will silence the
audible alarm. Depressing RESET a second time will reset the ratemeter
alarm and/or alert condition. The scaler alarm can only be reset by
depressing the scaler count switch located in the end of the Model 2241-3
handle.
Note:
The RESET button only silences the alarm in the current mode
that the instrument is in. For example, the RESET button will
not affect the scaler alarm if the instrument is in the
ratemeter mode.
Scaler Count Switch: pushbutton switch located in the end of the Model
2241-3 carrying handle, which when depressed, initializes the start of the
scaler count accumulation for the preset scaling time. The SCA/RATE switch
must be in the SCA position to initiate the counting cycle. The scaler display
uses the two digits in the lower right-hand corner for the two most
significant digits of the six-digit readout. Scaling time can be set from 1 to
9999 seconds in the parameter setup by way of the switch board. Depressing
the Count switch after a scaler alarm will reset the scaler display to 0,
resetting the alarm condition.
Front Panel Calibration Controls
Note:
Remove the front-panel calibration cover to expose the
following calibration controls:
DISC (Discriminator): a multi-turn potentiometer (approximately 20
revolutions) used to vary the detector pulse-counting threshold from 2 to
100 millivolts. A Ludlum Model 500 Pulser or equivalent should be used in
checking or adjusting the pulse discrimination parameter.