LUDLUM MODEL 2241-3 & 2241-3i SURVEY METER

LUDLUM MODEL 2241-3 & 2241-3i
SURVEY METER
November 2014
Serial Number 299171 and Succeeding
Serial Numbers
LUDLUM MODEL 2241-3 & 2241-3i
SURVEY METER
November 2014
Serial Number 299171 and Succeeding
Serial Numbers
Table of Contents
Introduction
Information on Model 2241-3i
Getting Started
1
1-2
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
3-1
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
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November 2014
Model 2241-3 & 3i Technical Manual
Instrument Setup
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 × 226
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
Ludlum Measurements, Inc.
November 2014
Model 2241-3 & 3i Technical Manual
1
Section 1
Section
Introduction
T
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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Model 2241-3 & 3i Technical Manual
Section 1
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.
Ludlum Measurements, Inc.
Page 1-2
November 2014
Model 2241-3 & 3i Technical Manual
2
Section 2
Section
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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Page 2-1
November 2014
Model 2241-3 & 3i Technical Manual
Section 2
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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Model 2241-3 & 3i Technical Manual
Section 2
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
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.
ALERT
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 S position should respond
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Page 2-3
November 2014
Model 2241-3 & 3i Technical Manual
Section 2
approximately five times slower than the F position (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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November 2014
Model 2241-3 & 3i Technical Manual
3
Section 3
Section
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
can display in either R/hr, Sv/h, cpm, or cps when the control
switch is in the RATEMETER position.
RATEMETER
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 setupHV 1, HV 2, HV 3, and HV 4, regulated within 0.2% at 1000 Vdc;
maximum load of 50 µA.
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Model 2241-3 & 3i
Technical Manual
Section 3
RESET:
a pushbutton for zeroing the display, acknowledging and/or
resetting the alarm.
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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Page 3-2
November 2014
Model 2241-3 & 3i Technical Manual
Section 3
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 × 109 counts/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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Page 3-3
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Model 2241-3 & 3i Technical Manual
Section 3
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%
2
Tube: 30 mg/cm
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)
Ludlum Measurements, Inc.
Page 3-4
November 2014
Model 2241-3 & 3i Technical Manual
4
Section 4
Section
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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Section 4
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 4 Switch:
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 F position allows the time constant (TC) to vary
from 1 to 10 seconds, while the S position 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.
Fixed Response:
The F position corresponds to the selected fixed response
time - TC. The S position 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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Section 4
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:
(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.
DISC
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Page 4-3
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Model 2241-3 & 3i Technical Manual
Section 4
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, HV3, HV4:
multi-turn potentiometers (approximately 20
revolutions) that vary the detector voltage from 400 to 2500 volts. The
maximum high-voltage output is adjusted by the HV LIMIT potentiometer
located on the internal main board.
Main Board Controls
Note:
To access the internal circuit boards, unlatch the latches at
each end of the Model 2241-3. 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
2500 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 position, the
clicks-per-event, or the audible alarm(s), will not be audible when active.
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Section 4
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 Model
2241-3 batteries are removed. After the parameters are entered, the switch
board can be removed and the Model 2241-3 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.
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Page 4-5
November 2014
Model 2241-3 & 3i Technical Manual
5
Section 5
Section
Safety Considerations
Environmental Conditions for Normal Use
Indoor or outdoor use
No maximum altitude
Temperature range of –20 to 50 °C (-4 to 122 °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.)
Detector Connector
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.
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.
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Model 2241-3 & 3i Technical Manual
Section 5
The Model 2241-3 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.
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
any 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. 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.
Ludlum Measurements, Inc.
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Model 2241-3 & 3i Technical Manual
6
Section 6
Section
Maintenance
Instrument maintenance consists of keeping the instrument clean and
periodically checking the batteries and the calibration. The Model 2241-3
may be externally cleaned 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:
1. Turn the instrument OFF and remove the batteries.
2. Allow the instrument to sit for one minute before performing
any external cleaning or accessing internal components for
maintenance.
Operational Check
An instrument operational check should be performed prior to each use by
exposing the detector to the supplied check source, confirming the proper
reading on each scale. See Section 2, Subsection “Operational Check,” for
further details.
Recalibration
Recalibration should be accomplished after any maintenance or adjustment
of any kind has been performed on the instrument. Battery and cable
replacements (of same length) and exterior cleanings do not normally require
the instrument be recalibrated.
Note:
Ludlum Measurements, Inc. recommends recalibration at
intervals no greater than one year. Check the appropriate local
state and federal regulations to determine required recalibration
intervals.
Ludlum Measurements, Inc.
Page 6-1
November 2014
Model 2241-3 & 3i Technical Manual
Section 6
Ludlum Measurements offers a full-service repair and calibration
department. We not only repair and calibrate our own instruments, but most
other manufacturers’ instruments as well.
See Section 8 “Instrument Setup & Calibration,” for further details on
instrument calibration.
Batteries
The batteries should be removed and the battery contacts cleaned of any
corrosion at least every three months. If the instrument has been exposed to
a very dusty or corrosive atmosphere, more frequent battery servicing should
be used. 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 the
batteries. Although this instrument will operate at very high
ambient temperatures, battery seal failure can occur at
temperatures as low as 38 °C (100°F).
Ludlum Measurements, Inc.
Page 6-2
November 2014
Model 2241-3 & 3i Technical Manual
7
Section 7
Section
Refer to the Main
Board schematic
for the following:
Technical Principle of Operation
Detector Input/Amplifier
Negative-going detector pulses are coupled from the detector through C021
to amplifier U021. R024 and CR021 protect the input of U021 from
inadvertent shorts. Self-biased amplifier U021 provides gain in proportion to
R022, divided by R025. Transistor pins 4, 5, and 6 of U021, provide
amplification. Pins 10-15 of U021 are coupled as a constant current source
to pin 6 of U021. The output is self-biased to 2 Vbe (approximately 1.4
volts) at pin 7 of U021. This provides just enough bias current through pin 6
of U021 to conduct all of the current from the constant current source.
Positive pulses from pin 7 of U021 are coupled to the discriminator (U011)
through R031 and C012.
Discriminator
Positive pulses from amplifier U021 are coupled to pin 2 of U011
comparator. The discrimination level is set by the DISC control connected
to pin 3 of U011. As the positive pulses at pin 2 of U011 increase above
DISC reference at pin 3, pin 1 goes low, producing a low pulse. Pin 1 of
U011 is normally held high (+5 volts) by R014.
The low pulse from pin 1 of U021 is coupled to univibrator U001. U001
shapes and fixes the pulse width to approximately 10 µs. The univibrator is
configured in the non-retriggerable mode. Negative pulses from pin 9 of
U001 are coupled to the µP for counting.
Low Voltage Supply
Battery voltage is coupled to DC-DC converter U231. U231 and related
components provide +5 V to power the µP, op-amps, and logic circuitry.
R135 and R136 provide voltage division for low-battery detection. Pin 6 of
U231 provides a low signal when the battery voltage decreases to +2.2 ±0.1
Vdc. U121 provides the +2.5 Vdc reference for the HV and DISC control
references.
Ludlum Measurements, Inc.
Page 7-1
November 2014
Model 2241-3 & 3i Technical Manual
Section 7
High Voltage Supply
High voltage is developed by blocking oscillator Q241, T141, and C244 and
rectified by voltage multiplier CR041-CR043, C041-C043, and C141. High
voltage increases as current through R241 increases, with maximum output
voltage with Q241 saturated.
High voltage is coupled back through R034 to op-amp pin 2 of U131.
Resistor network R027, R132 completes the HV division circuit to ground.
R027 provides HV limit from 1250-2400 when the HV control on the
calibration board is at maximum. The regulated HV output is controlled by
the HV1 and HV2 potentiometers located under the CAL cover on the
front panel. This control provides the reference for comparator pin 3, U131.
During stable operation, the voltage at pin 2 of U131 will equal the voltage
at pin 3 of U131. Pin 1 of U131 will cause conduction of Q141 to increase
or decrease until the HV finds a level of stability.
Microprocessor (µP)
U111 controls all of the data, control inputs, and display information. The
clock frequency is crystal-controlled by Y221 and related components at
6.144 MHz. The µP incorporates internal memory (ROM), storing the
program information. U1 resets the µP at power-up to initiate the start of
the program routine. During the program loop, the µP looks at all the input
switches for initiation or status changes and responds accordingly.
U122 is a 256 x 8 bit EEPROM used to store the setup parameters. The
information is transferred serially from the µP. The EEPROM is
non-volatile, meaning it retains memory even after power is removed.
Audio
Click-per-event, divide-by, and alarm audio pulse frequency is generated by
the µP and coupled to Q101. Q101 then inverts the pulses and drives the
bottom of T101. Bias voltage is provided by the volume control (R002) to
the top of T101.
Refer to the Switch
Board schematic for
the following:
Ludlum Measurements, Inc.
S1 (FUNCTION)
S1 is a 16-position binary rotary switch, which selects the programmable
parameters for the Model 2241-3. The switch selects the parameters using
the hexadecimal numbering system via buss lines SW1-SW4.
Page 7-2
November 2014
Model 2241-3 & 3i Technical Manual
Section 7
S2-S4
S2-S4 are pushbutton switches which enter/change the variables for each of
the 16 parameters.
U1
U1 is a +5 V powered RS-232 driver/receiver used to interface the Model
2241-3 to a computer.
Refer to Display
Board schematic
for the following:
LCD Drive
U111 and U211 are serial input 32-bit LCD drivers. The data is loaded
serially into the 32-bit shift registers (internal) via the “D” IN input. The
LOAD input instructs the shift register to receive data while the CLOCK input
shifts the data through the 32-bit registers. After all the data is loaded, the
LOAD line is pulsed by the µP, instructing the registers to transfer the data to
the LCD drivers. The backplane (BP) signal from U211 provides the
reference signal (approximately 125 Hz at 5 Vdc) to the LCD (DSP1) BP
connection. When a segment is illuminated, the signal to that segment will
be out-of-phase with the BP signal. If the segment is OFF, the signal will be
in-phase with the BP signal.
Backlight Drive
Depressing the LIGHT button instructs the µP to set the BACKLIGHT line, pin
31 on µP, "low" for the predetermined backlight ON time. (Refer to main
board schematic for details.) A "low" condition on pin 31 causes Q212 to
conduct sending +3 V to P8-3 on the display board with +3 V at P8-3
(refer to display board schematic). Backlight oscillator Q011, T011, and
related components start to oscillate, producing a 2.5 kHz, sine wave signal.
The signal is amplified by T011 to 150 volts peak-to-peak to drive the LCD
backlight.
Ludlum Measurements, Inc.
Page 7-3
November 2014
Model 2241-3 & 3i Technical Manual
8
Section 8
Section
Instrument Setup & Calibration
Entering or Changing Switch Board
Parameters
On the switch board, select the desired parameter to enter or change by
using the corresponding FUNCTION switch position. Depress the ENTER
button, and a character on the LCD will start to flash. The flashing character
indicates that the program is in the parameter change mode.
To change the character, press the UP button until the desired variable is
reached. To shift to another character, increment the LEFT pushbutton until
the desired character is reached. The LEFT pushbutton switch enables the
operator to sequence through all the characters on the LCD associated with
a particular parameter.
Once the desired data is entered, depress the ENTER button. The LCD
characters should stop flashing and the new parameter data should display.
Note:
The DETECTOR SELECT switch allows the Model 2241-3 to
have four sets of operating parameters.
Loading Default Parameters
To load the default parameters for all detector setups, hold down the UP
pushbutton on the switch board until DEF is displayed on the LCD. The
table on the following page shows the default values.
Ludlum Measurements, Inc.
Page 8-1
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
Model 2241-3
Dead Time
Cal Const
Rate Alarm
Scaler Alarm
Count Time
Time Base
Units
Audio Divide-By
Response
Check Source
Percent CS
Rate Alert
Cpm
Setup 01
0 µs
100e-2
50.0 kcpm
85000
12 s
Minutes
cpm
1
0
0
0
20.0 kcpm
Minimum Display
0.00 cpm
Baud Rate
LCD Time Off
Detector
uR/hr
Setup 02
0 µs
105e+8
50 µR/hr
85000
12 s
Seconds
R/hr
1
0
0
0
20 µR/hr
00.0
µR/hr
R/Hr
Setup 03
0 µs
108e+4
5 R/hr
85000
12 s
Seconds
R/hr
1
0
0
0
2 R/hr
00.0
µR/hr
mR/hr
Setup 04
0 µs
198e+6
5 mR/hr
85000
12 s
Seconds
R/hr
1
0
0
0
2 mR/hr
00.0
µR/hr
9600
5s
0
The Function Switch
FUNCTION Switch: a 16-position rotary switch labeled “0-9” and “A-F.”
This switch selects a parameter setup mode for the Model 2241-3. If the
board is not installed, the normal operation mode (counting mode) is
selected. If the switch board is installed, the selector switch must be set to
the 0 position for normal instrument operation. The following may be
changed using the switch board, and are discussed in detail in this section:
Detector parameters
Durrent detector setup in use
RS-232 communication baud rate
RS-232 data dump mode
RS-232 detector parameters set/read mode
Function Switch Position Descriptions and
Variables
POSITION 0: NORMAL OPERATION
places the Model 2241-3 in the normal
(counting) operating mode. Unplugging the switch board from the Model
2241-3 main board defaults to the normal operating mode.
Ludlum Measurements, Inc.
Page 8-2
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
POSITION 1:
DEAD TIME (µs) allows changing the detector dead time
correction for the current detector setup. Setting this parameter to “0”
disables dead time correction. The dead time adjusts from 0 to 9999
microseconds (µs). The incoming counts are adjusted for dead time using
the following formula:
n=
m
1 - m
Where,
n = corrected counts per second
m = incoming count per second
 = system dead time
CC =
cps x time base
rate
POSITION 2:
calibration constant allows changing the calibration constant
for the current detector setup. The calibration constant (CC) adjusts from
0.001 to 280 × 109. The calibration constant converts counts/time base to
units/time base. The CC must be set to 1 to readout in cps (counts per
second) or cpm (counts per minute).
CC CONVERSION TABLE
Conversion Rate
Multiply by to get CC
3.6 x 109
3.6 x 106
3.6 x 103
6.0 x 107
6.0 x 104
6.0 x 101
3.6 x 107
3.6 x 104
3.6 x 101
6.0 x 105
6.0 x 102
0.6
cps/µR/hr
cps/mR/hr
cps/R/hr
cpm/µR/hr
cpm/mR/hr
cpm/R/hr
cps/µSv/h
cps/mSv/h
cps/Sv/h
cpm/µSv/h
cpm/mSv/h
cpm/Sv/h
Example:
The Model 44-9 GM detector produces approximately 3300
cpm/mR/hr for 137Cs:  6.0 x 104 x 3300 = 198 x 106 for
CC.
Ludlum Measurements, Inc.
Page 8-3
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
POSITION 3: DISPLAY UNITS
selects the display units for the associated
detector setup number. The Model 2241-3 and detector may be calibrated in
either exposure rate (R/hr or Sv/h) by entering the appropriate Calibration
Constant (position 2) and Dead Time correction (position 1). The Model
2241-3 will automatically convert to the correct reading when switching
between R and Sv.
The time base for count “C” is set independently in position 4.
The display units may be set to:
R/hr (Roentgens per hour)
Sv/h (Sieverts per hour)
C/time base (Counts per time)
The display is auto-ranging with the appropriate multiplier
symbol appearing in front of the “R,” “Sv,” or “C,” indicating
the range:
µR/hr, mR/hr, R/hr
µSv/h, mSv/h, Sv/h
C/s, kC/s, C/m, kC/m
POSITION 4:
(TIME BASE) CPS or CPM selects the display time base for the
current detector setup. This time base only applies if the units are set to C/
(Counts/time). The time base for R/hr and Sv/h is fixed in “hr.” For
“true” reading (pulser calibration) cpm or cps calibrations, set the
Calibration Constant (CC, parameter 2) to read “1.” For geometry
calibrations, the detector efficiency can be entered for CC.
Example:
For alpha scintillation detector with 25% 2π efficiency; enter
“250 10-3” in the CC parameter setup.)
The display time base may be set to:
seconds (s)
minutes (m)
Ludlum Measurements, Inc.
Page 8-4
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
POSITION 5: AUDIO DIVIDE-BY
selects the audible click-per-event division
rate for the current detector setup. If the AUD ON/OFF switch is in the OFF
position, no audible click-per-event will be heard.
This parameter ranges from:
0 = Divide By 1
1 = Divide By 10
2 = Divide By 100
3 = Divide By 1000
POSITION 6: RESPONSE TIME
allows changing the time constant (TC) for
the current detector setup. If the response is set to 0, the Model 2241-3
automatically calculates (for variable mode) the time constant based on the
incoming cps. If a variable of 1-199 is entered for TC, the response time
becomes fixed.
Variable Response - Response time is varied in proportion to
the incoming count rate. The two-position F/S (Fast/Slow)
toggle switch selects the maximum time constant (TC) for the
variable mode. The fast position varies the TC from 4-25
seconds, and the slow position varies from 4-60 seconds.
Response - The Fast (F) response position is
programmable from 2-50 seconds, and the slow response is 5
times slower than the fast TC. For MDA-type measurements,
the fixed response time mode is recommended.
Fixed
POSITION 7: RATEMETER ALARM/ALERT allows changing the ratemeter
alarm for the current detector setup. The units of this alarm are the same as
the units for the ratemeter display. The fifth push of the left button allows
the decimal point to be moved. The ratemeter alarm adjusts from 1 to 999
R/hr (or Sv/h) or 1 to 999 kcpm or 1 to 100 kcps. The units of the alarm
are determined by the units for the ratemeter.
POSITION 8: SCALER ALARM/COUNT TIME
sets the scaler alarm variable
from 1-999999, corresponding to the accumulated scaler count. After the
scaler alarm variable is entered, the scaler count time is prompted. The scaler
count time is adjustable from 1-9999 seconds.
POSITION 9: NOT USED
Ludlum Measurements, Inc.
Page 8-5
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
POSITION A: NOT USED
POSITION B:
LCD Backlight ON TIME is the amount of time that the LCD
backlight will stay on after pressing the front panel switch labeled LIGHT.
This value is stored in EEPROM.
Available values are:
5 seconds
30 seconds
60, 90 seconds
180, 240 seconds.
POSITION C: SET MINIMUM DISPLAY
sets the ratemeter minimum
displayable reading. Depressing the RESET button displays the minimum
ratemeter units. The readout will auto-range up to the maximum displayable
but will display 0 for ratemeter readings below the user-programmed
minimum variable.
Minimum displayable values are:
00.0 µ, 000 µ, 0.00 m, 00.0 m, 000 m, 0.00, 00.0, 000 R/hr
.000 µ, 000 µ, 00.0 m, 000 m, 0.00, 00.0, 000 Sv/h
0.00, 00.0, 000, 0.00 k, 00.0 k, 000 kcpm, or cps
POSITION D: RS-232 DATA DUMP MODE allows the RS-232 port to dump
ratemeter data every two seconds. The Model 2241-3 is fully functional
during RS-232 data dump with the exception of the audio function. The
LCD will alternate between display of the ratemeter and the word “dUP”
(representing "dump").
POSITION E: RS-232 DETECTOR PARAMETERS SETUP MODE allows the RS232 port to accept/send a string of parameters corresponding to the current
detector setup values.
POSITION F: BAUD RATE configures the RS-232 port for the following baud:
150, 300, 600, 1200, 2400, 4800, 9600, and 19200. The data is eight data bits,
one stop bit with no parity bit. This value is stored in EEPROM. The baud
rate can only be programmed through the switch board.
Ludlum Measurements, Inc.
Page 8-6
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
RS-232 PORT CONNECTOR: This nine-pin “D” type connector is designed
as a DCE port. A straight wire cable (extension cable) connects the Model
2241-3 to a computer’s nine-pin RS-232 port.
RS-232 CONNECTOR PIN OUT:
PIN
FUNCTION
1
2
3
4
5
6
7
8
9
NC (No Connection)
DATA OUT
DATA IN
NC
NC
NC
HANDSHAKING IN
HANDSHAKING OUT
NC
Note:
Ludlum Measurements, Inc. offers a PC compatible software
program, which incorporates the read/write commands
necessary to communicate between the PC and the Model
2241-3. The program also incorporates an algorithm to
calculate the detector Calibration Constant and Dead Time
Constant. The software is offered in a DOS version (part
number 1370-025) or a WINDOWS version (part number
1370-024). Read the Software License Agreement at the end of
this section before installing any LMI software.
Calibration
The Model 2241-3 calibration routine consists of entering detector
parameters into memory by way of the switch board and adjusting the CAL
controls (HV and DISC) for the specific detector operating requirements.
The first subsection of calibration will give a general overview of detector
setup, including the determination of various detector operating voltages
(HV) and the adjustment of counter input sensitivity (DISC).
The next subsection deals with pulse generator counts-per-minute
calibration. The counts-per minute-parameter setup is used in the initial
Ludlum Measurements, Inc.
Page 8-7
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
instrument checkout procedure and the variables are saved under detector
setup number “1” when shipped from Ludlum Measurements, Inc.
The following subsection deals with exposure rate calibration. The detector
Calibration Constant (CC) and Dead Time Correction (DTC) are the two
primary parameters used in the exposure rate calibrations (R/hr and Sv/h).
These two constants are alternately varied to achieve linearity at the detector
non-linear operating regions. An example of the Ludlum Model 44-9 GM
detector calibration is given at the end of this section to illustrate the
algorithm used in determining the CC and DTC variables.
GENERAL DETECTOR SETUP INFORMATION
The operating point for the instrument and probes is established by setting
the probe voltage and instrument sensitivity (HV and DISC). The proper
selection of this point is the key to instrument performance. Efficiency,
background sensitivity, and noise are fixed by the physical makeup of the
given detector and rarely vary from unit to unit. However, the selection of
the operating point makes a marked difference in the apparent contribution
of these three sources of count.
In setting the operating point, the final result of the adjustment is to establish
the system gain so that the desirable signal pulses (including background
radiation) are above the discrimination level and the unwanted pulses from
noise are below the discrimination level and are therefore not counted.
The total system gain can be controlled by adjusting either the instrument
sensitivity or the high voltage. HV controls the gain of the detector; and DISC
(Discriminator) controls the instrument counting threshold (sensitivity).
In the special case of GM detectors, a minimum voltage must be applied to
establish the Geiger-Mueller characteristic. Further changes in HV will have
little effect on this type of detector.
GM Detectors:
The output pulse height of the GM detector is not
proportional to the energy of the detected radiation. Adjusting DISC will
have minimal effect on observed count rate unless the DISC setting is so low
that the instrument will double-pulse.
Ludlum Measurements, Inc.
Page 8-8
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
For most GM detectors, set DISC for 30-40 millivolts and adjust HV to the
GM detector recommended high voltage. Most GM detectors operate at
900 volts, although some miniature detectors operate at 450-550 volts. If a
recommended setting is unavailable, plot count rate versus HV to produce a
plateau graph. Adjust the HV for 25-50 volts above the knee or start of the
plateau. For mixed detector use, both sensitivity and high voltage may be
tailored for other detectors as long as the GM detector is operated within
the recommended voltage range. Caution must be observed in lowering the
input sensitivity to ensure that the counter does not double or multi-pulse.
Alpha Air-Proportional Detectors:
For air proportional alpha detectors, set
the DISC for 2 millivolt discrimination. Adjust HV until the detector just
breaks down (shown by a rapid increase of count rate without a source
present). Measure the HV output, then decrease the HV setting to operate
100 volts below breakdown.
Proportional Detectors: For proportional detectors, set the DISC control for
2-millivolt discrimination (near maximum clockwise). Expose the detector
to a check source and plot count rate versus HV, similar to the one in the
figure below. Refine the HV adjustment for optimum source efficiency with
a minimum acceptable background count.
Scintillators: Set the DISC for 10 millivolts. Plot background and
source counts versus HV to produce a plateau graph similar to the
one in the figure. Adjust the HV to 25-50 volts above the knee or
start of the plateau. This provides the most stable operating point
for the detector.
COUNTS PER MINUTE (C/M) CALIBRATION
This procedure will set up the Model 2241-3 for the Counts/minute (C/m)
mode of operation. Refer to Section 8, (Page 8-2 and following) for more
information on setup parameter variables.
A Ludlum Model 500 Pulser or equivalent is required. If the pulser does not
have a high-voltage display, use a high-impedance voltmeter with at least
1000 megohms input resistance to measure the detector high voltage.
Ludlum Measurements, Inc.
Page 8-9
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
Switch the SCA/RATE switch to the RATE position. Select
position DET1 on the detector selector switch located on the
front panel.
Select FUNCTION switch positions 1-6 and adjust for the
following parameters:
Switch Pos.
1
2
3
4
5
6
Parameter
Function
0000 s-6
0100 -2
c/
m
1
000 s
Dead Time
Calibration Constant
Display Units
Timebase
Audio Divide-by
Response Time
Position 7 selects the desired ratemeter ALERT and ALARM trip points.
If the parameters are undetermined, arbitrarily choose “0050
kC/m” for the alarm and “0045 kC/m” for the alert to confirm
operation of the alert/alarm function.
Position 8 selects the scaler alarm parameter and the scaler count time.
If the values are unknown, set the scaler alarm to “4500ALARM00”
and the count time to “0060” (60 second count time).
Position 9 is not used, and position A is not used.
Switch to position B and enter “15” for a 15-second backlight
ON time.
Switch to position C and enter “00.0 C/m” for the minimum
displayable value.
Select position 0 to return to normal operation.
Connect the Model 500 Pulser to detector input and adjust HV and DISC to
the specific detector operating parameters.
Ludlum Measurements, Inc.
Page 8-10
November 2014
Model 2241-3 & 3i Technical Manual
Section 8

Adjust the pulser amplitude to 1.5 times the Model 2241-3
discrimination level.

Adjust the pulser output to 800 cpm and confirm that the Model
2241-3 reads 800 cpm ±10% on the ratemeter setting.

Adjust the pulser output to 200 cpm and confirm that the Model
2241-3 reads 200 cpm ±10% on the ratemeter setting.

Adjust the pulser output to 800 cpm, take a one minute count and
confirm that the digital scaler readout displays 800 cpm ±2%.

Adjust the pulser output to 200 cpm, take a one minute count and
confirm that the digital scaler readout displays 200 cpm ±2%.

Confirm that the 20% and 80% readings for the upper decades are
within the pulser input by decading the pulser count output.

Confirm that the scaler readout is within 2% of the pulser input rate.

Ensure that the ALERT and ALARMs function by inputting the preset
alarm levels as to initiate the alert and alarm conditions.
R/hr CALIBRATION
The following calibration procedure assumes that detector Calibration
Constant (CC) and Dead Time Constant (DTC) are already known. If these
constants must be determined, reference the following subsection,
“Determining CC and DTC.”
Switch the toggle switch to DET2. Detector setup number “1” is usually
reserved for the Counts/minute parameter calibration. Rotate the
FUNCTION switch counterclockwise to position 1 and enter the detector
Dead Time in µs. Rotate to position 2 and enter the Calibration Constant.
Enter the desired parameters for positions 3-F. Switch to position 0 for
normal operation.
Expose the detector to calibrated radiation fields extending from the lower
to the upper operating range of the detector. Confirm that the linearity is
within 10% of each respective reading. If the readings are off on the lower
detector operating region, vary CC. If the readings are off at the upper end
of the detector operating region, adjust DTC.
Ludlum Measurements, Inc.
Page 8-11
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
DETERMINING CC AND DTC
This procedure contains the algorithm (hi-lo method) for determining the CC
(Calibration Constant) and the DTC (Dead Time Correction). An example
of the Ludlum Model 44-9 GM detector calibration is used in conjunction
with the algorithm calculations to aid in solving the equations.
Note:
Ludlum Measurements, Inc. offers a PC-compatible software
program, which incorporates the read/write commands
necessary to communicate between a PC and the
Model 2241-3. The program also incorporates the algorithm to
calculate the detector CC and DTC. The software is offered in
a DOS version (part number 1370-025) or a WINDOWS
version (part number 1370-024). Read the Software License
Agreement at the close of this section prior to installing any
LMI software.
Hi-Lo Method:
The hi-lo method refers to the placement of the detector in a
radiation field using a two-point (CC and DT) calibration to make linear the
detector response, even in the non-linear operating regions of the detector.
The low-radiation field (CC) should be a field that yields from 2 to 5 %
count loss. The high radiation field (DT) should be a field that yields from
30 to 60 % count loss. The algorithm ignores background counts, and
therefore, the low field must be at least ten times the background count.
The following summary lists the calibration constraints.
Calibration and Dead Time Calibration Constraints
FIELD
CONSTRAINT
BACKGROUND
*10 times less than low field
LOW FIELD
Yields from 2 to 5 % count loss
HIGH FIELD
Yields from 30 to 60 % count loss
* This constraint only applies when using two sources (two fields) or a
radiation range calibrated without background consideration.
Ludlum Measurements, Inc.
Page 8-12
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
Preliminary CPS Setup
Refer to Section 8, Subsection “Function Switch Position Descriptions and
Variables,” for cps readout variables.
Select position DET1 on the detector selector switch located on the front
panel. Starting with FUNCTION switch position 1, enter the following
variables:
SWITCH POS.
Equation 1
CPS LO 2% =
1
49 x DT
PARAMETER
1
2
3
4
5
6
7
8
9
A
B
C
D-F
0000s-6
0100 -2
C/
m
N/A
N/A
N/A
0060 s
Not Used
Not Used
N/A
000 C/s
N/A
FUNCTION
Dead Time
Calibration Constant
Display Units
Timebase
Audio Divide-By
Response Time
Ratemeter Alm./Alert
ScalerAlm./Count Time
LCD Backlight
Set Minimum Display
RS-232 Parameters
Equation 2
CPS LO 5% =
1
19 x DT
Equation 3
CPS HI 30% =
1
2.3333 x DT
Equation 4
CPS
HI
60%
=
The equations to the left (Equations 1-4) determine the hi and lo radiation
fields used to acquire counts for the CC and DTC algorithm. These
calculations require an unknown variable, DT (Dead Time). Typical dead
times for some of the standard LMI detectors are referenced in the table at
the end of this section. The lo count field should be a field that yields
between 2 and 5% count loss. The hi count field (CPSHI) should be a field
that yields between 30 and 60% count loss.
1.5
DT
Ludlum Measurements, Inc.
Page 8-13
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
Reference the table at the end of this section to determine the cps/exposure
rate (cps/ER). The conversion can be determined by placing the detector in
a radiation field, which produces from 50
to 200 cps. Calculate the count/exposure
= cps / ER rate using the equation to the left.
cps
radiation field in exposure rate units
For example, exposing an LMI Model 449 to a 2 mR/hr 137Cs field yields approximately 110 cps so that:
110 cps
= 55 cps/mR/hr
2 mR/hr
The typical dead time for a Model 44-9 is approximately 85 µs. Therefore,
using 85 µs for “DT” in equations 1-4, the lo field should be between 240
and 619 cps, and the hi field is between 5040-17,650 cps. Dividing the cps
values by the 55 cps/mR/hr conversion equates to between 4-11 mR/hr for
the lo field and 91-320 mR/hr for the hi field.
Select a calibrated field between the lo and hi data points determined above:
lo (CALlo) = 8 mR/hr
hi (CALhi) = 200 mR/hr
The following procedure outlines the hi-lo method
Abbreviations used:
units = Sv, R, counts.
CALlo = lo field calibration point.
CALhi = hi field calibration point.
CORRlo = recorded field at low calibration point.
CORRhi = recorded field at high calibration point.
DT = dead time constant entered into Model 2241.
CC = calibration constant entered into Model 2241.
fd and ad are intermediate steps in calculating DT.
fcal is an intermediate step in calculating CC.
Ludlum Measurements, Inc.
Page 8-14
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
CC and DTC Algorithm
Equations (5) and (6) convert units per time (R/hr Display Units) to units
per second:
units
units

second
time
Insert the cps lo data point (8 mR/hr for the Model 44-9 example)
determined from equations (1) and (2):
Equation 5
CALlo = (0.008
1h
1m
R
) x(
) x(
) = 2.22 x 10 6 s
h
60 m
60 s
Insert the cps hi data point (200 mR/hr for the Model 44-9 example)
determined from equations (3) and (4):
Equation 6
CALhi = (0.200
R
1h
1m
) = 55.6 x 10 6 s
)x (
)x (
h
60 m
60 s
Place the detector in the low field and enter the counts per second:
Equation 7
CORRlo =
SAMPLlo
=
count time
counts
s
Note:
The low field count sample should be  3000 counts. Use the
scaler and adjust the count time to accumulate count  3000.
Ludlum Measurements, Inc.
Page 8-15
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
As an example, assume a 60-second count sample in a low field of 8
mR/hr:
Example
CORR
lo
26,427
60
=
=
440 C/s
Place detector in the high field and enter the counts per second:
Equation 8
CORR
hi
SAMPL hi
=
count time
=
counts
s
Counts/second sample in high field of 200 mR/hr:
Example
CORR
hi
=
5830
=
1
5830 C/s
Insert the values calculated in equations (5), (6), (7), and (8) and solve for fd:
Equation 9
f
d
= CAL
hi
-
CORR hi x CAL
CORR lo
lo
units
s
=
Example
f
d
= 55.6 x 10
6
-
5830 x 2.22 x 10
440
6
=
26.2 x 10
6
s
Solve for ad:
Equation 10
a d = ( CAL
hi
x CORR
hi
) - ( CAL lo x CORR
hi
)=
units  count
s
2
Example
6
6
a d = (55.6 x 10 x 5830) - (2.22 x 10 x 5830) =
Ludlum Measurements, Inc.
Page 8-16
31.1 x 10  6
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
Enter the results of equations (9) and (10) into equation (11) to solve for
DT:
Equation 11
DT =
f
d
s
count
=
ad
Example
DT =
26 . 2 x10  6
=
31 . 1 x10  2
8 . 4 x10
6
s
Solve for fcal:
Equation 12
f
cal
= CAL
lo
- ( CAL
lo
x CORR
lo
x DT) =
units
s
Example
f cal = 2.22 x 10  6 - (2.22 x 10  6 x 440 x 84 x 10  6 ) =
2.14 x 10  6 s
Enter the result of equation (12) into:
Equation 13
CC = CORR
f cal
lo
count
units
=
and solve for CC:
Example
CC =
440
2.14 x 10
6
=
206 x 10
6
Enter the CC and DT values (positions 1 and 2 of the FUNCTION switch),
derived from the equations above. Perform an “R/hr calibration” as
described in the previous subsection in order to ensure that the instrument
and detector have been correctly calibrated.
Ludlum Measurements, Inc.
Page 8-17
November 2014
Model 2241-3 & 3i Technical Manual
Section 8
Model 44-9 Detector Parameter Setup
FUNCTION
PARAMETER
1
2
4
5-8
B-C
D-F
0084 s-6
0206 06
N/A
as desired
as desired
if applicable
Typical Count Rate and Dead Time for LMI Detectors
MODEL & TYPE
COUNT RATE
44-6, GM
44-9, GM
44-7, GM
133-2, GM
133-4, GM
133-6, GM
44-2, Gamma Scint.
44-10, Gamma Scint.
44-3, Low-Energy Gamma Scint.
44-21, Beta/Gamma Scint.
43-5, Alpha Scint.
DEAD TIME
in µs (microseconds)
20 cps/mR/hr
55 cps/mR/hr
35 cps/mR/hr
17.5 cps/mR/hr
2 cps/mR/hr
0.3 cps/mR/hr
2800 cps/mR/hr
15,000 cps/mR/hr
N/A, operated in Counts/units mode
N/A, operated in Counts/units mode
N/A, operated in Counts/units mode
90-110 µs
80-90 µs
240-290 µs
40-55 µs
40-55 µs
40-55 µs
8-12 µs*
18-20 µs
8-12 µs*
8-12 µs*
20-28 µs
Note:
The data represented in the table above is typical. Actual values
may vary among detector and instrument combinations. This
table represents some of the common detectors operated with
the Model 2241-3. Consult the LMI sales department for
information concerning detectors not listed in the table above.
*The dead time values for these scintillation detectors are due to the dead
time of the Model 2241-3 electronics.
Ludlum Measurements, Inc.
Page 8-18
November 2014
Model 2241-3 & 3i Technical Manual
Ludlum Measurements, Inc.
Section 8
Page 8-19
November 2014
Model 2241-3 & 3i Technical Manual
Ludlum Measurements, Inc.
Section 8
Page 8-20
November 2014
Model 2241-3 & 3i Technical Manual
Ludlum Measurements, Inc.
Section 8
Page 8-21
November 2014
Model 2241-3 & 3i Technical Manual
9
Section 9
Section
Recycling
L
udlum Measurements, Inc. supports the recycling of the electronic
products it produces for the purpose of protecting the environment
and to comply with all regional, national, and international agencies
that promote economically and environmentally sustainable
recycling systems. To this end, Ludlum Measurements, Inc. strives to supply
the consumer of its goods with information regarding reuse and recycling of
the many different types of materials used in its products. With many
different agencies – public and private – involved in this pursuit, it becomes
evident that a myriad of methods can be used in the process of recycling.
Therefore, Ludlum Measurements, Inc. does not suggest one particular
method over another, but simply desires to inform its consumers of the
range of recyclable materials present in its products, so that the user will
have flexibility in following all local and federal laws.
The following types of recyclable materials are present in Ludlum
Measurements, Inc. electronic products, and should be recycled separately.
The list is not all-inclusive, nor does it suggest that all materials are present in
each piece of equipment:
Batteries
Glass
Aluminum and Stainless Steel
Circuit Boards
Plastics
Liquid Crystal Display (LCD)
Ludlum Measurements, Inc. products, which have been placed on the
market after August 13, 2005, have been labeled with a symbol recognized
internationally as the “crossed-out wheelie bin.” This notifies the consumer
that the product is not to be mixed with unsorted municipal waste when
discarding. Each material must be separated. The symbol will be placed near
the AC receptacle, except for portable equipment where it will be placed on
the battery lid.
The symbol appears as such:
Ludlum Measurements, Inc.
Page 9-1
November 2014
Model 2241-3 & 3i Technical Manual
Section 10
Section
10
Model 2241-3
Survey Meter
Main Circuit Board,
Drawing 408 × 285
CAPACITORS
Ludlum Measurements, Inc.
Parts List
Reference
Description
Part Number
UNIT
Completely Assembled
Model 2241-3 Survey Meter
48-2864
Completely Assembled
Main Circuit Board
5408-285
0.1µF, 50V
0.1µF, 50V
47pF, 100V
0.001µF, 100V
0.1µF, 50V
100pF, 3KV
0.0047µF, 3KV
100pF, 3KV
0.0047µF, 3KV
0.0047µF, 3KV
47uF, 10V
47uF, 10V
27pF, 100V
0.0047µF, 3KV
0.1µF, 50V
0.01µF, 50V
47µF, 10V
0.01µF, 50V
47µF, 10V
100pF, 100V
0.001µF, 100V
0.0047F, 3KV
04-5663
04-5663
04-5660
04-5659
04-5663
04-5532
04-5547
04-5532
04-5547
04-5547
04-5666
04-5666
04-5658
04-5547
04-5663
04-5664
04-5666
04-5664
04-5666
04-5661
04-5659
04-5547
BOARD
C1
C3
C001-C002
C011
C012
C021
C031
C032
C033
C041-C043
C101
C121
C122-C123
C131
C132-C133
C134
C135
C136
C137
C138
C139
C141
Page 10-1
November 2014
Model 2241-3 & 3i Technical Manual
Section 10
Reference
Description
Part Number
C241
C242
C243
C251
1µF, 35V
68µF, 10V
0.1µF, 50V
68µF, 10V
04-5656
04-5654
04-5663
04-5654
TRANSISTORS
Q101
Q141
Q211
Q212
Q241
2N7002L
MMBT3904LT1
2N7002L
MMBT4403LT1
MJD210 RL
05-5840
05-5841
05-5840
05-5842
05-5843
INTEGRATED
CIRCUITS
U1
U001
U011
U021
U111
U121
U122
U131
U231
MAX810LEUR
CD74HC4538M
TLC372ID
CA3096M; 16=GND
N87C51FC
LM285MX-2.5
X24C02S8T5
LM358D
LT1073CS8-5
06-6424
06-6297
06-6290
06-6288
06-6303
06-6291
06-6299
06-6312
05-5852
DIODES
CR021
CR031
CR041-CR044
CR231
CR241
CR242
MMBD7000LT1
GI250-2
GI250-2
CXSH-4 EB33
MMBD914LT1
CXSH-4 EB33
07-6355
07-6266
07-6266
07-6358
07-6353
07-6358
R002
R027
10K; 3269X1-103, VOLUME
1M; 3269X1-105, HV LIMIT
09-6921
09-6906
R001
R011-R012
R013
R014
R015
R021
R022
R023
R024-R025
100K, 1/4W, 1%
10K, 1/4 W, 1%
1K, 1/4W, 1%
10K, 1/4W, 1%
100K, 1/4W, 1%
1M, 1/4W, 5%
392K, 1/8W, 1%
10K, 1/4W, 1%
4.75K, 1/4W, 1%
12-7834
12-7839
12-7832
12-7839
12-7834
10-7028
12-7841
12-7839
12-7858
POTENTIOMETERS /
TRIMMERS
RESISTORS
Ludlum Measurements, Inc.
Page 10-2
November 2014
Model 2241-3 & 3i Technical Manual
Section 10
Reference
Description
Part Number
R026
R031
R032
R033-R034
R111-R113
R121
R122
R131
R132
R133
R134
R135
R136
R141
R211
R231
R241
R242
8.25K, 1/8W, 1%
4.7M, 1/4W, 5%
1M, 1/4W, 5%
1G, FHV-1, 2%
22.1K, 1/4W, 1%
100Ohm, 1/4W, 1%
6.81K, 1/4W, 1%
1M, 1/4W, 1%
511K, 1/8W, 1%
750K, 1/4W, 1%
1M, 1/4W, 1%
82.5K, 1/8W, 1%
10K, 1/4W, 1%
22.1K, 1/4W, 1%
2.21K, 1/4W, 1%
100Ohm, 1/4W, 1%
2.21K, 1/4W, 1%
200Ohm, 1/8W, 1%
12-7838
10-7030
10-7028
12-7686
12-7843
12-7840
12-7857
12-7844
12-7896
12-7882
12-7844
12-7849
12-7839
12-7843
12-7835
12-7840
12-7835
12-7846
CRYSTALS
Y221
6.144 MHZ, 2=GND, 3=GND
01-5262
INDUCTOR
L231
100uH, CTX100-2
21-9740
TRANSFORMERS
T101
T141
4275-083, AUDIO
L8050
4275-083
40-0902
MISCELLANEOUS
P1-P2
P3
P4
P5
1-640456-3, MTA100X13
640456-6, MTA100X6
640456-2, MTA100X2
1-640456-2, MTA100X12
13-8100
13-8095
13-8073
13-8061
BOARD
Completely Assembled
Calibration Board
5408-113
1M, HV1 SET
100K, DISC.
1M, HV2 SET
1M, HV3 SET
1M, HV4 SET
09-6814
09-6813
09-6814
09-6814
09-6814
Calibration Board,
Drawing 408 × 98
POTENTIOMETERS
Ludlum Measurements, Inc.
R115
R116
R117
R118
R119
Page 10-3
November 2014
Model 2241-3 & 3i Technical Manual
Section 10
Reference
Description
Part Number
RESISTORS
R110
R111
R112
R113
R114
R120
1M, 1/3W
10K, 1/3W
1M, 1/3W
1K, 1/3W
1M, 1/3W
1M, 1/3W
12-7751
12-7748
12-7751
12-7750
12-7751
12-7751
CONNECTOR
P7
CONN-640456-7, MTA100
13-8115
BOARD
Completely Assembled
Display Board
5408-259
Display Board,
Drawing 408 × 259
CAPACITORS
C1
27PF, 100V
04-5658
INTEGRATED
CIRCUITS
U1
U2
AY0438-I/L
AY0438-I/L
06-6358
06-6358
RESISTORS
R001-R004
R005
10.0K, 1%, 125mW
392 Ohm, 1%, 1/8 W
12-7839
12-7054
MISCELLANEOUS
J1
DS1
DSP1
CONN-640456-8, MTA100
EL-BACKLIGHT-LED
MAIN DISPLAY;
LCD-8246-365-4E1-A/W-REV1
13-8039
07-6527
Ludlum Measurements, Inc.
Page 10-4
07-6383
November 2014
Model 2241-3 & 3i Technical Manual
Switch Board,
Drawing 408 × 45
Section 10
Reference
Description
Part Number
BOARD
Completely Assembled
Switch Board
5408-052
CAPACITORS
C1-C2
C3-C4
C5
C6
4.7µF, 10V
10µF, 20V
4.7µF, 10V
100µF, 10V
04-5578
04-5592
04-5578
04-5576
INTEGRATED
CIRCUITS
U1
MAX220EPE
06-6359
SWITCHES
S1
S2
S3
S4
350134GSK; FUNCTION;
16 POS
LEFT
UP
ENTER
08-6721
08-6716
08-6716
08-6716
RESISTORS
R1-R2
22K
10-7070
MISCELLANEOUS
P6
P10
CONN-1-640456-3, MTA100
CONN-208006-2
13-8100
13-8451
S1
S2
S3-S4
S5
S6
S7
*
30-1-PB GRAYHILL
PA-1012
7101-SYZ-QE C&K
30-1-PB GRAYHILL
7201KZQE Toggle
MPS-103F
Switch Cap
08-6517
08-6540
08-6511
08-6517
08-6749
08-6699
08-6871
RESISTOR
R1
10 M, 1/4W, 5%
10-7031
CONNECTORS
J1 J2
J3
J4
J5
J6
J7
J8
J9
J10
P10
CONN-1-640442-3, MTA100
CONN-640442-6, MTA100
CONN-640442-2, MTA100
CONN-1-640442-2, MTA100
CONN-1-640442-3, MTA100
CONN-640442-7, MTA100
CONN-640442-8, MTA100
Series "C" -UG706/U
JACK-09-9011-1-4193
Handle Pin
13-8138
13-8171
13-8178
13-8407
13-8138
13-8172
13-8184
13-7777
18-9080
7408-055
Chassis Wiring
Diagram, Drawing
408 × 101
SWITCHES
Ludlum Measurements, Inc.
Page 10-5
November 2014
Model 2241-3 & 3i Technical Manual
Section 10
Reference
Description
Part Number
AUDIO
DS1
UNIMORPH
21-9251
BATTERY
B1-B2
˝D˝ Duracell Battery
21-9313
MISCELLANEOUS
*
Model 2241 Switch
Board Add On
Model 2241 Digital
Bezel Assembly
Portable Battery Contact Set
Model 2241-3 Main Harness
Portable Harness Can Wires
Switch Board Harness
Portable Can Assembly (MTA)
Can Gasket
Portable Knob
Assembled Battery Lid
Portable Battery Gasket
Portable Calibration
Cover with Screws
Model 2241-3 Flat Handle
Assembly without Clip
Cable-C 1 meter (39 in.) only
Model 2241-3 Casting
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Ludlum Measurements, Inc.
Page 10-6
4408-053
4408-051
2001-042
8408-121
8363-462
8408-027
4363-441
22-9773
08-6613
2363-191
7363-183
9363-200
4408-179
40-1004
7408-185
November 2014
Model 2241-3 & 3i Technical Manual
Section 11
Section
11
Drawings
Main Circuit Board, Drawings 408 × 285 (3 sheets)
Main Circuit Board Component Layout, Drawing 408 × 286
Calibration Board, Drawing 408 × 98
Calibration Board Component Layout, Drawings 408 × 99 (2 sheets)
Display Board, Drawing 408 × 259
Display Board Component Layout, Drawings 408 × 260 (2 sheets)
Switch Board, Drawing 408 × 45
Switch Board Component Layout, Drawing 408 × 46
Wiring Diagram, Drawing 408 ×101
Wiring Diagram for Model 2241-3i, Drawing 408 × 263
Ludlum Measurements, Inc.
Page 11-1
November 2014
Model 2241-3 & 3i
Technical Manual
Appendix A
Appendix
A
RS-232 Output Formats
The Ludlum Model 2241 series of instruments has an RS-232 serial
communications port that can be used to log readings and read or set
instrument parameters. There are two formats available. Most Model 2241
instruments have the binary format outlined below, but some newer Model
2241-2 units have an ASCII output, which is also outlined below following
the binary format explanation.
The RS-232 port is configured at 9600 baud, 8 data bits, no parity, and 1
stop bit (9600,8,N,1). Ludlum Measurements can supply a Windows-based
software that can be used to help calibrate the instruments, but note that it
will not communicate with the newer ASCII output Model 2241-2 units.
Binary Output Format (15 Bytes)
BYTE01
BYTE02
BYTE03
BYTE04
BYTE05
BYTE06
BYTE07
BYTE08
BYTE09
BYTE10
BYTE11
BYTE12
BYTE13
BYTE14
BYTE15
RatemeterCPS+0
RatemeterCPS+1
RatemeterCPS+2
RatemeterCPE+3
Scaler+0
Sclaer+1
Scaler+2
Scaler+3
Scaler+4
CountTime+0
CountTime+1
CountTimeLeft+0
CountTimeLeft+1
Carriage Return (0DH)
Line Feed (0AH)
MSB
LSB
MSB
LSB
MSB
LSB
MSB
LSB
The ratemeter value is in cps and is scaled by a factor of 256. To get the
ratemeter reading in cpm, take the value and divide by 256, and then
multiply by 60.
Ludlum Measurements, Inc.
Page A-1
November 2014
Model 2241-3 & 3i
Technical Manual
Appendix A
RS-232 Commands
E – auto dump off
A – auto dump on
C – start scaler
F – set scaler count time
R – send parameters from instrument to computer
S – read parameters from computer to instrument
O – output once
All commands must be sent in upper case laters.
Output of “R” Command – Read Parameters
BYTE01
Detector+0
BYTE02
DeadConstant+0
MSB
BYTE03
DeadConstant+1
LSB
BYTE04
CaConstant+0
MSB
BYTE05
CalConstant+1
BYTE06
CalConstant+2
BYTE07
CalConstant+3
BYTE08
CalConstant+4
BYTE09
CalConstant+5
LSB
BYTE10
RateAlarm+0
MSB
BYTE11
RateAlarm+1
BYTE12
RateAlarm+2
BYTE13
RateAlarm+3
BYTE14
RateAlarm+4
LSB
Ludlum Measurements, Inc.
BYTE15
BYTE16
BYTE17
BYTE18
BYTE19
BYTE20
BYTE21
BYTE22
BYTE23
BYTE24
BYTE25
ScalerAlarm+0
ScalerAlarm+1
ScalerAlarm+2
ScalerAlarm+3
ScalerAlarm+4
CountTime+0
CountTime+1
Units+0
TimeBase+0
AudioDivideBy+0
Response+0
BYTE26
BYTE27
BYTE28
BYTE29
BYTE30
BYTE31
BYTE32
BYTE33
RateAlert+0
RateAlert+1
RateAlert+2
RateAlert+3
RateAlert+4
CheckSource+0
CheckSource+1
CheckSource+2
Page A-2
MSB
LSB
MSB
LSB
MSB
LSB
MSB
November 2014
Model 2241-3 & 3i
Technical Manual
BYTE34
BYTE35
BYTE36
BYTE37
BYTE38
BYTE39
CheckSource+3
CheckSource+4
PercentCS+0
MinDisplay+0
Carriage Return (0DH)
Line Feed (0AH)
Appendix A
LSB
Input of “S” Command – Send Parameters
BYTE1
DeadCosntant+0
MSB
BYTE2
DeadConstant+1
LSB
BYTE3
CalConstant+0
MSB
BYTE4
CalConstant+1
BYTE5
CalConstant+2
BYTE6
CalCosntant+3
BYTE7
CalConstant+4
BYTE8
CalConstant+5
LSB
BYTE9
RateAlarm+0
MSB
BYTE10
RateAlarm+1
BYTE11
RateAlarm+2
BYTE12
RateAlarm+3
BYTE13
RateAlarm+4
LSB
Ludlum Measurements, Inc.
BYTE14
BYTE15
BYTE16
BYTE17
BYTE18
BYTE19
BYTE20
BYTE21
BYTE22
BYTE23
BYTE24
ScalerAlarm+0
ScalerAlarm+1
ScalerAlarm+2
ScalerAlarm+3
ScalerAlarm+4
CountTime+0
CountTime+1
Units+0
TimeBase+0
AudioDivdeBy+0
Response+0
BYTE25
BYTE26
BYTE27
BYTE28
BYTE29
BYTE30
BYTE31
BYTE32
BYTE33
BYTE34
BYTE35
BYTE36
RateAlert+0
RateAlert+1
RateAlert+2
RateAlert+3
RateAlert+4
CheckSource+0
CheckSource+1
CheckSource+2
CheckSource+3
CheckSource+4
PercentCS+0
MinDisplay+0
Page A-3
MSB
LSB
MSB
LSB
MSB
LSB
MSB
LSB
November 2014
Model 2241-3 & 3i
Technical Manual
Appendix A
Input of “F” Command – Set Count Time
BYTE1
CountTime+0
MSB
BYTE2
CountTime+1
LSB
Units
Timebase
1 = Sv
2 = cpm
0=R
0 = min
1 = seconds
AudioDivide
0 = Auto
1 = Manual
ASCII Output Format
This special firmware changes the format of the auto-dump from binary to
ASCII. The output interval remains the same (2 seconds).
2241
2241-2
2241-3
Special Firmware 40804n10
Special Firmware 40806n13
Special Firmware 40806n16
08/06/2003
04/04/2003
07/07/2004
The old format was (binary):
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Byte 9
Byte 10
Byte 11
Byte 12
Byte 13
Byte 14
Byte 15
Ratemeter CPS + 0
Ratemeter CPS + 1
Ratemeter CPS + 2
Ratemeter CPS + 3
Scaler + 0
Scaler + 1
Scaler + 2
Scaler + 3
Scaler + 4
Count Time + 0
Count Time + 1
Count Time Left + 0
Count Time Left + 1
Carriage Return (0DH)
Line Feed (0AH)
and is now replaced with (ASCII):
byte 1
byte 2
byte 3
byte 4
byte 5
byte 6
byte 7
Ludlum Measurements, Inc.
x
Ratemeter
x
Raetemter
x
Ratemeter
x
Ratemeter
x
Ratemeter
y
Display units
Carriage Return (0DH)
Page A-4
November 2014
Model 2241-3 & 3i
Technical Manual
byte 8
Appendix A
Line Feed (0AH)
The ratemeter is displayed as 5 ASCII digits with a decimal, if necessary, and
matches the LCD display on the 2241-2.
The display mode is a value from 0 to 9 representing the display units.
CPS
KCPS
CPM
KCPM
µR
mR
R
µSv
mSv
Sv
0
1
2
3
4
5
6
7
8
9
Note: The LMI Model 2241 calibration software is not compatible with this
firmware version.
Example output:
02.991
01.801
01.221
00.831
00.581
004160
Ludlum Measurements, Inc.
(=2.99 kcps)
(=1.80 kcps)
(=1.22 kcps)
(=0.83 kcps)
(=0.58 kcps)
(=416 cps)
Page A-5
November 2014