Ludlum Measurements 25 User manual

LUDLUM MODEL 25 AND 25-1
PERSONAL RADIATION MONITOR
USER’S MANUAL
October 2014
Serial Number 25000100 and Succeeding
Serial Numbers

LUDLUM MODEL 25 AND 25-1
PERSONAL RADIATION MONITOR
USER’S MANUAL
October 2014
Serial Number 25000100 and Succeeding
Serial Numbers

Model25and25-1PersonalRadiationMonitor User’s Manual
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Instrument Operational Test 2-1
Instrument Use and Controls 2-3
Distinguishing ALERTs and ALARMs 2-6
Specifications 3
Calibration and Changing Parameters 4
Calibration Overview 4-1
Entering SETUP Mode and Changing Parameters 4-2
Calibration Procedure 4-3
Safety Considerations 5
Environmental Conditions for Normal Use 5-1
Warning Markings and Symbols 5-1
Cleaning and Maintenance Precautions 5-2
Revision History 6
Recycling 7

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Introduction
he Model 25 and 25-1 is a personal radiation detection and
warning instrument. The instrument features a large backlit LCD
(liquid crystal display), a bright (daylight-visible) warning light, and
a piercing audio warning. The unit body is made of lightweight
but durable plastic and can survive brief immersion in water. The Model 25
may be clipped to a belt or worn around the neck with a lanyard.
The Model 25-1 readout is in mSv/h or Sv/h, whereas the Model 25
readout is in mR/hr or R/hr. This being the only difference between the
two, this manual will refer to the two instruments as “Model 25.”
The detector inside the Model 25 measures gamma radiation up to 999
R/hr (9.99 Sv/h). The display, which normally shows exposure rate, will
also display total accumulated dose, and time remaining. In an alarm
situation, the display (automatically backlit if light levels are dim) rotates
every two seconds among the three displays: exposure rate, accumulated
dose, and time remaining. Thus, in an emergency situation, a responder can
be warned of the radiation level and informed of the time remaining before
their maximum allowed dose is reached.
Setup of the instrument is accomplished also through the front-panel
buttons. The advanced user or administrator can set ALERT and ALARM
levels (both exposure rate and accumulated dose), change calibration
parameters, and zero the total accumulated dose within the setup routine.
The unit is operated with two coin cell batteries for operation from -40 to
65 °C (-40 to 150 °F). Battery life should be approximately 6000 hours
under non-alarming conditions. A low-battery indicator on the LCD warns
when less than eight hours of battery life remain.
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Getting Started
Unpacking and Repacking
Remove the calibration certificate and place it in a secure location. Remove
the instrument and accessories (lanyard, case, 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 25 serial
number is located on the back panel below the battery compartments.
To return an instrument for repair or calibration, provide sufficient
packing material to prevent damage during shipment.
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
Open each battery lid by using a large coin or screwdriver to unscrew
(counter-clockwise) the two round battery holders on the back of the
instrument. Remove the two old batteries, and replace with new batteries.
Ensure that both batteries have the plus (+) sign facing outwards. Screw
each battery holder clockwise until the holder is flush with the case. Battery
replacement may be done by the user, and is not considered a reason for
recalibration.
Instrument Operational Test
Turn the instrument ON by pressing the ON/ACK button for about a
second, and then releasing. The instrument should activate all the LCD
segments, the audio, and the warning light. It then displays a version
number before displaying the current exposure rate, normally 0.0 mR/hr (or
.000 mSv/h.
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Ensure that the low-battery indicator is not present. If the low-battery
indicator is present, replace the batteries as soon as possible. Under
extremely low battery conditions, be aware that the unit may not even turn
on, or may turn itself off abruptly.
If possible, expose the detector to a source of radiation. Small check sources
of radiation are available from Ludlum Measurements. While exempt from
many regulations because of their small size, these sources are large enough
to produce a response on this instrument. The detector's position is marked
by the small plus (+) sign on the front panel of the Model 25. A typical 1
µCi (37 kBq) 137Cs check source will produce an exposure rate of
approximately 3 mR/hr (.003 mSv/h). If this procedure is done routinely
with the same radiation source, instrument malfunction may be detected
when anomalous readings are observed.
A reference reading with a check source should be obtained 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.
Note that the Model 25 has its own diagnostic tests to ensure that the
detector is functioning correctly. The Model 25 can detect when the
radiation detector is malfunctioning and will flash “0.0 mR/hr” (.000
mSv/h) with “F,” the warning audio, and the light to indicate a detector
malfunction. If this indication is observed, remove the unit from service
and have it evaluated by a qualified repair and calibration technician.
Once this procedure has been completed, the instrument is ready for use.

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Instrument Use and Controls
With only two front-panel buttons, the Ludlum Model 25 is simple and easy
to use with minimal training required. Under typical use, the display shows
just the current exposure rate. Whenever the MODE button is pressed, or
during an ALERT or ALARM condition, the display rotates among the
exposure rate, the total accumulated dose, and the time remaining (in
hh:mm format). The additional display modes may help the user to decide
how long to stay in a high-radiation area.
See the Model 25 front-panel drawing at the beginning of this manual
to reference the following two controls:
ON/ACK button: Used to power the Model 25 ON and OFF, and
acknowledge audio on alerts and alarms.
ON: Press for approximately one second and release (all LCD
segments will activate, and firmware version will be shown).
OFF: Press for approximately five seconds (audio will beep and
LCD will clear).
ACK (acknowledge): Will silence audio during an ALERT or
ALARM condition, but in an ALARM condition the audio will
continue to be activated once every 60 seconds to remind the user.
MODE button: When pressed under non-alarm conditions, the display
rotates between the total accumulated dose, the time remaining, and back to
the normal exposure rate display. If the light is very dim, pressing the
MODE button will also turn on the backlight while the display cycles
among the three display modes.
The Exposure Rate (main active screen) at typical background radiation
levels shows a number similar to 0.04 mR/hr. Figure 1 (on the following
page) also shows the low-battery icon.

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Figure 1: The Exposure Rate Screen shows typical background radiation rate and the low-
battery icon.
Zeroing Accumulated Dose: In order to “zero” the accumulated dose, the
user must enter the setup mode, and then not press any other buttons. The
parameters will change every four seconds, and the unit will return
automatically to the normal mode after the last parameter is presented. The
accumulated dose has now been reset to zero.
The Accumulated Dose screen is shown in Figure 2. 80.5 R is a significant
dose, and thus Figure 2 also shows the ALARM indication.
Figure 2: Accumulated Dose Screen with ALARM indicator

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The Time Remaining screen shown in Figure 3 displays 10 hours and 30
minutes (10:30) remaining before the user receives the maximum allowed
accumulated dose. An ALERT indication is also shown in Figure 3.
Figure 3: Time Remaining Screen with ALERT indication
OVER icon: Whenever the calibrated range (9.99 Sv/h or 999 R/hr) is
exceeded, the OVER icon is activated. This is to alert the user that the
Model 25 Radiation Monitor is out of range. The display will also flash
the maximum displayed value (9.99 Sv/h or 999 R/hr).

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Distinguishing ALERTs and ALARMs
There are four independent radiation alarms:
Exposure Rate ALERT: distinguished by the word ALERT in the
exposure rate display and a slow, single beep of the audio.
Exposure Rate ALARM: distinguished by the word ALARM in the
exposure rate display and a fast, single beep of the audio.
Accumulated Dose ALERT: distinguished by the word ALERT in
the accumulated dose display and a slow, double beep of the audio.
Accumulated Dose ALARM: distinguished by the word ALARM in
the accumulated dose display and a fast, double beep of the audio.
Note that an ALARM condition will override a lower priority ALERT
condition.
The audible alarms consist of a single frequency tone and are easily
distinguishable from the Personal Alert Safety System (PASS) alarms
typically worn by firefighters.

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Specifications
0
Detector High Voltage: internally fixed at 550 Vdc
Linearity: reading within 10% of true value within calibration range
Accuracy: within 10%
Angular Response: <25% deviation from 137Cs response, detector axis parallel
to field
Gamma Response: typically 18 cpm per mR/hr (1800 cpm per mSv/h)
Beta Response: typically <0.10 mR/hr (< .001 mSv/h) with a 101 kdpm
90SrY beta source on contact
Neutron Response: typically 0.3 mR/hr ( .003 mSv/h) in a 10 mrem/hr (0.1
mSv/h) neutron field from a brass shielded Am-Be source
Response Time: varies by exposure rate, faster response times with high
exposure rates; normally under 10 seconds from <1 to 10 mR/hr ( 0.1 mSv/h),
2 seconds or less from <1 to 50 mR/hr (0.5 mSv/h)
Energy Dependency: within 15% of true value (60 keV to 3MeV)
Maximum Accumulated Dose: limited by display, 999 R for the Model 25
and 9.99 Sv for the Model 25-1
Display: backlit 1.3 cm (0.5 in.) digits with readings from .001 to 999, or from
00:01 to 19:59 in hours/min format, indications of (m)R(/hr), (m)Sv(/h),
ALERT, ALARM, a low-battery symbol, and OL (over limit)
Display range: for Model 25: 0.01 mR/hr to 999 R/hr
for Model 25-1: .001 mSv/h to 9.99 Sv/h
Calibrated range (exposure rate): normally calibrated from 2 mR/hr (0.02
mSv/h) to 999 R/hr (9.99 Sv/h)
Self-Diagnostics: If no pulses are received from the detector in 60 minutes,
instrument failure is indicated by an audible and visual alarm, and the display
alternating between “0.0” and “F.”
Battery Dependence: less than 3% change in readings to battery failure
indication
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End-of-Battery Life Warning: At approximately 2.3 Vdc, the low-battery
symbol is displayed on the front-panel LCD, indicating that eight hours of use
remain. Below 2.0 Vdc, the unit may abruptly turn off (blank the display).
Calibration Controls: Front-panel buttons provide setup routine to view or
change ALERT and ALARM setpoints, calibration constants, and to zero the
accumulated dose.
Audio: built-in speaker with a typical intensity of 95 dB at 30.5 cm (1 ft) at a
frequency of 3.5 kHz
Power: two DL2450 (NEDA/ANSI/IEC #5029LC) coin cell batteries
housed in two externally accessible compartments
Battery Life: typically 6000 hours under non-alarm conditions
Size: 7.6 x 5.4 x 1.7 cm (3.0 x 2.1 x 0.69 in.) (H x W x thickness)
Weight: 144 g (5.1 oz), including batteries
Temperature Range: -40 to 65 °C (-40 to 150 °F)
Construction: injection-molded plastic body
Note: This instrument is not intended for measuring of background levels of
radiation.

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Calibration and Changing
Parameters
Warning!
Only advanced users or administrators should consider changing
any of the parameters in the following section. Incorrect settings
could jeopardize the safety of users depending on this instrument.
Calibration Overview
Your instrument has been shipped from Ludlum Measurements only after
passing electronic checkout, a 30-hour burn-in process, and a careful calibration
process. Calibration papers are supplied with each instrument shipped from
Ludlum Measurements.
Recalibration should be accomplished after maintenance or adjustments have
been performed on the instrument. Recalibration is not normally required
following instrument cleaning or battery replacement. Recalibration does not
require any special tools or software to perform.
Ludlum Measurements offers a full-service repair and calibration department.
Not only do we repair and calibrate our own instruments, we also service most
other manufacturers’ instruments. Calibration procedures are available upon
request for customers who choose to calibrate their own instruments.
Note:
Ludlum Measurements, Inc. recommends recalibration at intervals
no greater than two years, assuming that regular operational
checks are performed. Check the appropriate local, state, and
federal regulations to determine required recalibration intervals.
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Note: Calibration of the Model 25 requires a gamma radiation source (typically
137Cs that is traceable to a national standard or other suitable reference, and can
produce radiation fields from 2 mR/hr (02 mSv/h) to 800 R/hr (8 Sv/h).
Before calibrating the instrument, the user may wish to adjust the ALERT and
ALARM setpoints to 999.
Entering SETUP Mode and Changing
Parameters
Calibration involves the changing of parameters, accessed via the SETUP mode.
The following parameters are adjustable to suit the user’s needs (default values
are in parentheses). Radiological alert and alarm parameters are values
recommended by the National Council on Radiation Protection and
Measurements (NCRP).
Rate Alert (10 mR/hr) (0.1 mSv/h)
Rate Alarm (10 R/hr) (0.1 Sv/h)
Dose Alert (10 R) (0.1 Sv)
Dose Alarm (50 R) (0.5 Sv)
Calibration Constant (300 cps/R/hr) ( 300 cps per 0.01 Sv/h)
Dead Time Constant (30 µsec)
Series Constant (285)
NOTE: Successful completion of the SETUP mode also zeros the
accumulated dose. Powering down (by pressing the ON/ACK button) will
result in change to parameters or the accumulated dose.
Entering Setup Mode
To enter setup mode, power down the Model 25, then turn the unit back ON.
When “0.00 mR/hr” (“.000 mSv/h”) appears on the LCD, press the MODE
button three times within four seconds to enter Setup Mode. You will know
that the unit is in SETUP mode when the display suddenly changes to “10
mR/hr ALERT” (or whatever the current rate alert is set to). If you simply wish
to view the parameters, you may do so by not pressing any other buttons. The
parameters will change every four seconds when no buttons are pressed. The
unit will return automatically to normal mode after the last parameter is
presented.
Using Setup Mode to Change Parameters
Once the Model 25 is in SETUP mode, the Rate Alert Setpoint should be
displayed on the LED, and the units for the Rate Alert Setpoint

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(mR/hr, R/hr, mSv/h, or Sv/h) should be blinking. For the first four
parameters (Rate Alert, Rate Alarm, Dose Alert, and Dose Alarm), there are five
items to adjust, namely :
Units (mR/hr, R/hr, mSv/h, or Sv/h)
Number of Decimal Places (0, 1, or 2)
Ones Place (0-9)
Tens Place (0-9)
Hundreds Place (0-9)
NOTE: The remaining parameters do not have the option to change the units
or the number of decimal places.
Use the MODE button to toggle the options for the selected item. When the
appropriate value is selected for that item, press the ON/ACK button to adjust
the next item.
When the desired Rate Alert Setpoint is displayed, simply wait for four seconds.
The Model 25 will then switch to the next parameter (Rate Alarm Setpoint in
this case).
NOTE: If no buttons are pressed for four seconds, the Model 25 will switch
to the next parameter, and if on the last parameter, will save the parameters and
exit SETUP mode.
Repeat this process until all of the setup parameters are set to the desired values.
After the last setup mode (Series Constant), the Model 25 will resume normal
activity after four seconds of inactivity.
Calibration Procedure
Expose the instrument to a radiation field of 80 mR/hr (0.8 mSv/h) and adjust
the Calibration Constant until the Model 25 display reads within 10% of 80.0
mR/hr (0.8 mSv/h). Expose the instrument to a radiation field of 80 R/hr (0.8
Sv/h), and adjust the Dead Time Constant until the Model 25 display reads
within 10% of 80.0 R/hr (0.8 Sv/h).
Expose the instrument to a radiation field of 800 R/hr (8 Sv/h), and adjust the
Series Constant until the Model 25 display reads within 10% of 800 R/hr (8
Sv/h).
Record and document the following readings, and verify that all of the readings
are within 10% of the appropriate radiation field:
2 mR/hr (0.02 mSv/h) and 8 mR/hr 0.08 mSv/h)
20 mR/hr (0.2 mSv/h) and 80 mR/hr (0.8 mSv/h)

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200 mR/hr (2 mSv/h) and 800 mR/hr (8 mSv/h)
2 R/hr (0.02 Sv/h) and 8 R/hr (0.08 Sv/h)
20 R/hr (0.2 Sv/h) and 80 R/hr (0.8 Sv/h)
200 R/hr (2 Sv/h) and 800 R/hr (8 Sv/h)
Reset the ALERT and ALARM setpoints to the desired levels. Record all
parameters.

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Safety Considerations
Environmental Conditions for Normal Use
Indoor or outdoor use
No maximum altitude
Temperature range of -40 to 65 °C (-40 to 150 °F)
Maximum relative humidity of less than 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.)
Not certified for use in an explosive atmosphere
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.
The Model 25 Survey Meter is marked with the following symbols:
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. Be sure to take the precautions noted in
the next section whenever necessary.
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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 serial
number label located on the back panel. See section 7, “Recycling,” for
further information.
The “CE” mark is used to identify this instrument as being acceptable for
use within the European Union.
Cleaning and Maintenance Precautions
The Model 25 may be cleaned externally with a damp cloth, using only
water as the wetting agent. Observe the following precautions when
cleaning or performing maintenance on the instrument:
1. Turn the instrument OFF and remove the batteries.
2. Allow the instrument to sit for one minute before cleaning the
exterior or accessing any internal components for maintenance.