Ludlum Measurements 2241-4 User manual

LUDLUM MODEL 2241-4
SURVEY METER WITH
NEUTRON DETECTOR
October 2022
Serial Number 170658 and Succeeding
Serial Numbers

LUDLUM MODEL 2241-4
SURVEY METER WITH
NEUTRON DETECTOR
October 2022
Serial Number 170658 and Succeeding
Serial Numbers
Model 2241-4 with
Model 42-31H Detector

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. October 2022
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-2
Detector Connection 2-2
Operational Check 2-2
Specifications 3
Instrument 3-1
Removable Switchboard Adjustable Parameters 3-2
Model 42-31H Neutron Detector 3-3
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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Ludlum Measurements, Inc. Page 1-1 October 2022
Instrument Setup & Calibration 8
Entering or Changing Switch Board Parameters 8-1
Loading Default Parameters 8-1
The Function Switch 8-2
Function Switch Position Descriptions and Variables 8-3
Calibration 8-8
General Detector Setup Information 8-8
Counts per Minute (C/m) Calibration 8-10
R/hr Calibration 8-11
Detector CC and DTC 8-12
Software License Agreement 8-19
Recycling 9
Parts List 10
Model 2241-4 Survey Meter 10-1
Main Circuit Board, Drawing 408 × 223 10-1
Calibration Board, Drawing 408 × 12 10-3
Display Board, Drawing 408 × 259 10-4
Switch Board, Drawing 408 × 45 10-5
Chassis Wiring Diagram, Drawing 408 × 103 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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Ludlum Measurements, Inc. Page 1-1 October 2022
Introduction
he Model 2241-4 is a portable microprocessor-based digital Scaler/
Ratemeter coupled to a Model 42-31H Neutron Detector for use in
measuring and monitoring neutron radiation. Data is presented on a
four-digit (six digits in the scaler mode) Liquid Crystal Display
(LCD) with moving decimal point. A three-position switch labeled
˝OFF/RATEMETER/SCALER˝ selects the desired operating mode for the
instrument.
Programmable display units (RATEMETER mode only) are represented in
R/hr (normally represents roentgens/hr, but in this application represents
rem/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 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
alarm, indicating that the counting circuitry is nearing the maximum
counting capability.
Section
1
T
Similar Instrument with
Model 42-31H Detector

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Ludlum Measurements, Inc. Page 1-2 October 2022
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 and independent set-point control,
adjustable from 400 to 2400 volts, with detector overload detection and
adjustable discrimination levels add versatility to the instrument. All of the
calibration controls are covered to prevent any inadvertent adjustments 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 attached Ludlum Model 42-31H Neutron Detector is designed for
detection of thermal and fast neutrons (0.025 eV to approximately 12
MeV). The neutrons are detected, not directly, but through nuclear
reactions, which result in energetically charged particles, such as alpha
particles. In many instances intense fields of gamma rays are also found
with neutrons. Therefore, it is important to choose a method of neutron
detection with the ability to discriminate against these gamma rays in the
detection process.
A common reaction for the conversion of slow neutrons into directly
detectable particles is n+3He→3H+1H + 0.764 MeV.
The Ludlum Model 42-31H utilizes this reaction in the form of helium-
3(3He), which fills the gas proportional tube of the detector
The Model 42-31H is designed to be used with portable counting
instruments and has a top bracket that allows for convenient mounting of
a portable instrument. The Model 42-31H consists of a 3He detector (1.6
cm diameter x 2.5 cm thick), surrounded by a cadmium-loaded
polyethylene sphere, 22.9 cm (9 inches) in diameter. A study is available
that shows that the 9-inch cadmium-loaded sphere has a response similar
to that of a 10-inch diameter rem-responding sphere.

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Ludlum Measurements, Inc. Page 2-1 October 2022
Getting Started
Unpacking and Repacking
Remove the calibration certificates and place them in a secure location.
Remove the instrument, detector, 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 2241-4 serial number is located on the front panel below the battery
compartment. To access the Model 42-31H detector identification, perform
the following: (1) loosen the thumbscrews; (2) rotate counterclockwise and
remove the polyurethane sleeve from the sphere; and (3) pull the detector
from sleeve. The identification is located on the detector shaft. Reassemble
in reverse order. Removal of the air-seal screw from the end of the
polyurethane sleeve will facilitate reassembly. Replace the screw once the
detector is completely reassembled.
Important!
If multiple shipments are received, ensure that the detectors
and instruments are not interchanged. Each instrument is
calibrated to a specific detector(s), and is 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.
Section
2