LUDLUM 2241-2i User manual

LUDLUM MODEL 2241-2i AND -2i/2
SURVEY METER
January 2018
Serial Number 170658 and Succeeding
Serial Numbers

LUDLUM MODEL 2241-2i AND -2i/2
SURVEY METER
January 2018
Serial Number 170658 and Succeeding
Serial Numbers

Ludlum Measurements, Inc. January 2018

Ludlum Measurements, Inc. January 2018
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 2018
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Operational Check 2-2
Specifications 3
Instrument 3-1
Removable Switchboard Adjustable Parameters 3-2
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
Recalibration 6-1
Batteries 6-2
Technical Theory of Operation 7
Main Board 7-1
Switch Board 7-3
Display Board 7-3

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Instrument Setup 8
Entering or Changing Switch Board Parameters 8-1
The Function Switch 8-1
Function Switch Position Descriptions and Variables 8-2
Loading Default Parameters 8-6
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
Detector Overload (OVL) Calibration 8-19
Software License Agreement 8-21
Recycling 9
Parts List 10
Model 2241-2i and 2241-2i/2 Survey Meter 10-1
Main Circuit Board, Drawing 408 × 223 10-1
Calibration Board, Drawing 408 × 120 10-3
Display Board, Drawing 408 × 259 10-4
Switch Board, Drawing 408 × 45 10-4
Chassis Wiring Diagram, Drawing 408 × 123 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 2241-2i and 2241-2i/2 are portable microprocessor-based
digital Scaler/ Ratemeter instruments designed for use with
scintillation, Geiger-Mueller (GM), and proportional type detectors
to measure ionizing radiation. Data is presented on a four-digit (six
digits in the scaler mode) Liquid Crystal Display (LCD) with a moving
decimal point. A three-position switch labeled OFF/RATEMETER/SCALER
selects the desired operating mode for the instrument.
A toggle switch labeled ˝INT/EXT˝allows the user to select between internal
and external detector. The internal detector is an energy compensated GM
tube capable of measuring fields up to 4 R/hr (0.04 Sv/h) for the Model
2241-2i and up to 1 R/hr (0.01 Sv/h) for the Model 2241-2i/2.
Programmable display units (RATEMETER mode only) are represented in
either 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 to 1 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 Dead Time Correction (DTC) to compensate for
detector dead time; audible click-per-event with programmable 1, 10, 100,
and 1000 divide-by; LCD backlight with programmable ON time;
programmable fixed or variable response time; and count overflow visual
Section
1
T

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alarm, indicating that the counting circuitry is nearing the maximum
counting capability.
All of the features described above may be programmed manually using the
internal switch board or by computer through the RS-232 port. Two
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, two independent set-point controls
adjustable from 400 to 2400 volts with detector overload detection, 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.

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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
survey meter 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 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/SCALER/RATEMETER switch is in the OFF position. Open
the battery lid by turning the quarter-turn thumb screw counterclockwise
Section
2

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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:
Center post of battery is positive. The batteries are placed in
the battery compartment in opposite directions.
Operational Check
Connect a detector to the survey meter by using the cable provided; firmly
pushing the connectors together while twisting clockwise until the connector
latches (one-quarter turn). The diagram to the left illustrates how this is
done. Next, place the detector selector (INT/EXT) switch in the desired
position.
Turn the OFF/SCALER/RATEMETER switch to the RATEMETER 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 SCALER position, a single 0 will
be displayed.
The display will auto-range to the current level (see figure at left). When
auto-ranging down, the survey meter 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 uR/hr.
If using a Ludlum Model 44-2 detector, a typical reading
would be 1.4-2.6 kcpm or 8-15 uR/hr.
Expose the detector to a check source and verify that the instrument
indicates within 20% of the check source reading obtained during the last

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calibration. Alternatively, expose the detector to a source of known value
and verify that the detector detects greater than or equal to the efficiency
listed in the detector manuals’ specification section. Failure to meet these
criteria may indicate a detector malfunction.
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 OFFposition; 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, “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
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 meter is displaying low
numbers, which require a more stable display. The fast response position is
used at high count levels.
Move the OFF/SCALER/RATEMETER switch to the SCALER 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, INT/EXT and RATEMETER or SCALER parameters and
proceed to use the instrument.

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Specifications
0
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.
Warm-up Time: Unit may be used immediately after the LCD
initialization sequence is completed (approximately five seconds after
power-up).
Display: a four-digit Liquid Crystal Display (LCD) with digits one half
inch in height. Two additional 0.5 cm (0.2 in.) 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, counting OVERFLOW, and scaler
COUNTING.
Internal Detector Range: up to 10 R/hr
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.
Linearity: Readings are within 10% of true value with a detector
connected.
SCALER: activated by pushbutton in handle when the three-position
switch is in the SCALER position. Count time is adjustable.
Section
3
Instrument:

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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
Overload: indicated by OVERLOAD on the display; adjust-
able depending on the detector selected
High Voltage: two independent controls, each adjustable
from 400-2400 volts. There are two separate set points for
INT and EXT. It is 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
LIGHT: display backlight activated by pushbutton
Audio: built-in audio speaker (unimorph) with AUD ON/OFF switch;
greater than 60 dB at 0.61 m (2 ft)
Alert/Alarm: indicated by either an ALERT or ALARM enunciator on the
display (RATEMETER mode only) and by an audible tone
Temperature Range: -20 to 50 °C (-4 to 122 °F)
Size: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x W x L)
Weight: 1.6 kg (3.5 lb), including batteries.
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 uR/hr.
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.
Removable
Switchboard
Adjustable
Parameters:

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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 × 109
counts/display unit
Display Units: can display in R/hr, Sv/hr, cpm, or cps
Display Range: auto ranging from 0.0 µR/hr –9999 R/hr; 0.000 µSv/h
–9999 Sv/h; 0 cpm –999k cpm; or 0 cps –100k 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: This is 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 to 25
resulting in a FAST response from approximately 2 to 50
seconds. The SLOW response is approximately 10 to 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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Identification of Controls and
Functions
Display
The Model 2241-2i and 2241-2i/2 utilize a four-digit liquid crystal display
(LCD) with 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 annunciators 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
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mode when the six-digit display (four digits display and two overflow
digits in right corner) reaches ˝999999˝and starts to roll over again.
OVERLOAD: Indicates that the detector is being exposed to radiation
intensities greater than the detector maximum operating limit. For alpha
and/or beta-type scintillation detectors, an OVERLOAD may indicate that
the detector face has been punctured, allowing external light to saturate
the photomultiplier tube inside the detector. The overload alarm point
is set by adjusting the OVL control located underneath the calibration
cover.
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
INT/EXT (Detector Select) Switch:a toggle switch used to select
between internal detector (INT) and external detector (EXT) parameters
OFF/RATEMETER/SCALER Switch: a three-position rotary switch that
applies power to the instrument and selects RATEMETER or SCALER
counting mode
AUD ON/OFF Switch: The clicks-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
clicks-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/S” TC variables.

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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.
RESET Pushbutton Switch: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
survey meter handle.
Scaler COUNT Switch:Pushbutton switch located in the end of the
survey meter carrying handle, which when depressed, initializes the start
of the scaler count accumulation for the preset scaling time. The
SCALER/RATEMETER switch must be in the SCALER 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.

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Note:
When making adjustments to the HV potentiometers, make
note of the following precautions: Use a Ludlum Model 500
Pulser or high-impedance voltmeter with a high-voltage probe
to measure the high voltage at the detector connector. If a
Ludlum Model 500 Pulser is not available, ensure that the
impedance of voltmeter used is 1000 megohms or greater.
HV1, HV2:multi-turn potentiometers (approximately 20 revolutions)
that vary the detector voltage from 200 to 2500 volts for INT and EXT
respectively. The maximum high-voltage output is adjusted by the HV
LIMIT potentiometer located on the internal main board.
OVL (Detector Overload): a multi-turn potentiometer (approximately 20
revolutions) that adjusts the detector current level that must be exceeded
to initiate an OVERLOAD alarm. This control adjusts the current level
discrimination point from 0.5 and 40 microamperes, corresponding to
the specific detector saturation point.
Main Board Controls
Note:
To access the internal circuit boards, unlatch the latches at
each end of the survey meter. Carefully separate the top chassis
from the bottom cover (referred to as a "can"). The can has
the audio speaker (unimorph) with a two-conductor cable
attached to the main board. The audio plug may be
disconnected during the internal control adjustments.
HV LIMIT (R027): a multi-turn potentiometer (approximately 20
revolutions) sets the maximum HV limit with the front-panel HV control
adjusted to the maximum clockwise position. It is adjustable from 1250
to 2400 Vdc.
VOLUME (R002): A multi-turn potentiometer (approximately 20
revolutions) varies the audible click-per-event and alarm audio. Adjust
the control to the maximum clockwise position for maximum volume.
If the VOLUME control is adjusted to the maximum counterclockwise

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position, the clicks-per-event or the audible alarm(s) will not be audible
when active.
Switch Board Controls
The switch board utilizes a 16-position rotary switch (FUNCTION) to select
the 16 setup parameters. (Refer to schematics and component layout
drawing near the end of the manual.) All of the setup parameters are stored
in the non-volatile EEPROM, which will retain data even after the survey
meter batteries are removed. After the parameters are entered, the switch
board can be removed and the survey meter will continue to operate from
the previously programmed information. Changing parameters and
information on switchboard controls are covered in detail in Section 8 of
this manual.