Fluke 481 User manual

April 2011, Rev.1, 9/13
© 2011, 2013 Fluke Corporation. All rights reserved. Specifications are subject to change without notice.
All product names are trademarks of their respective companies.
481
Ion Chamber Survey Meter
Operators Manual
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - TestEquipmentDepot.com

LIMITED WARRANTY AND LIMITATION OF LIABILITY
Each Fluke product is warranted to be free from defects in material and workmanship under normal use and
service. The warranty period is one year and begins on the date of shipment. Parts, product repairs, and
services are warranted for 90 days. This warranty extends only to the original buyer or end-user customer of
a Fluke authorized reseller, and does not apply to fuses, disposable batteries, or to any product which, in
Fluke's opinion, has been misused, altered, neglected, contaminated, or damaged by accident or abnormal
conditions of operation or handling. Fluke warrants that software will operate substantially in accordance
with its functional specifications for 90 days and that it has been properly recorded on non-defective media.
Fluke does not warrant that software will be error free or operate without interruption.
Fluke authorized resellers shall extend this warranty on new and unused products to end-user customers
only but have no authority to extend a greater or different warranty on behalf of Fluke. Warranty support is
available only if product is purchased through a Fluke authorized sales outlet or Buyer has paid the
applicable international price. Fluke reserves the right to invoice Buyer for importation costs of
repair/replacement parts when product purchased in one country is submitted for repair in another country.
Fluke's warranty obligation is limited, at Fluke's option, to refund of the purchase price, free of charge repair,
or replacement of a defective product which is returned to a Fluke authorized service center within the
warranty period.
To obtain warranty service, contact your nearest Fluke authorized service center to obtain return
authorization information, then send the product to that service center, with a description of the difficulty,
postage and insurance prepaid (FOB Destination). Fluke assumes no risk for damage in transit. Following
warranty repair, the product will be returned to Buyer, transportation prepaid (FOB Destination). If Fluke
determines that failure was caused by neglect, misuse, contamination, alteration, accident, or abnormal
condition of operation or handling, including overvoltage failures caused by use outside the product’s
specified rating, or normal wear and tear of mechanical components, Fluke will provide an estimate of repair
costs and obtain authorization before commencing the work. Following repair, the product will be returned to
the Buyer transportation prepaid and the Buyer will be billed for the repair and return transportation charges
(FOB Shipping Point).
THIS WARRANTY IS BUYER'S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL OTHER
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY
OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. FLUKE SHALL NOT BE LIABLE
FOR ANY SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES OR LOSSES,
INCLUDING LOSS OF DATA, ARISING FROM ANY CAUSE OR THEORY.
Since some countries or states do not allow limitation of the term of an implied warranty, or exclusion or
limitation of incidental or consequential damages, the limitations and exclusions of this warranty may not
apply to every buyer. If any provision of this Warranty is held invalid or unenforceable by a court or other
decision-maker of competent jurisdiction, such holding will not affect the validity or enforceability of any other
provision.
11/99

i
Table of Contents
Title Page
Introduction............................................................................................ 1
Intended Use ......................................................................................... 1
Safety Information ................................................................................. 2
How to Contact Fluke ............................................................................ 4
Features ................................................................................................ 5
Overrange Rate ................................................................................. 5
Low Battery Indicator......................................................................... 5
Audio Alarm ....................................................................................... 5
Integrate Mode .................................................................................. 5
Freeze Mode ..................................................................................... 5
Auto-On Backlight.............................................................................. 5
Specifications ........................................................................................ 6
Receiving Inspection ............................................................................. 8
Operation............................................................................................... 9
External Controls ............................................................................... 9
ON/OFF Button.............................................................................. 9
Mode Button .................................................................................. 9
Freeze Mode ................................................................................. 10
Integrate Mode .............................................................................. 10
Self-Test ........................................................................................ 11
Installation ......................................................................................... 11
Operational check.............................................................................. 12
Optional Check Source Use .............................................................. 12
Theory of Operation .............................................................................. 13
Maintenance.......................................................................................... 15
Routine Cleaning ............................................................................... 16
Storage .............................................................................................. 16
Battery Replacement ......................................................................... 16
Replaceable Parts Information .......................................................... 17
Recalibration and Service Information................................................... 18
Troubleshooting................................................................................. 18
Self-Test Failure ............................................................................ 18
High Background Readings........................................................... 18
Erratic Readings ............................................................................ 18

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iii
List of Tables
Table Title Page
1. Symbols..................................................................................................... 2
2. Bar Graph Display Update Periods ........................................................... 14
3. Replaceable Parts List .............................................................................. 17

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v
List of Figures
Figure Title Page
1. Fluke 481 Ion Chamber Survey Meter ...................................................... 4
2. Battery Access .......................................................................................... 17

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1
Introduction
The Model 481 Ion Chamber Survey Meter (the Survey Meter) is a hand-held,
battery operated meter designed to measure beta above 100 keV and gamma
and x-ray radiation above 7 keV, using the latest CMOS and LCD technology.
The Survey Meter case is constructed of high strength ABS plastic. A gasket and
desiccant pack seal moisture out of the Survey Meter and provide a cushion for
the internal components. The readout consists of a 2½ digit liquid crystal display
and a 100 segment analog bar graph. The bar graph contains a zero segment
and 20 groups of five segments each. A permanent scale is located on the
display screen. The major divisions of the scale indicate the units corresponding
to the range that the meter is measuring. The units of measurement show next to
the 2½ digit display. LOW BAT and FREEZE appear on the display when the
Survey Meter is operating in these modes. External controls consist of an
ON/OFF button and a MODE button. The Survey Meter is auto-ranging and auto-
zeroing. The auto-on circuit for the backlight is enabled when twilight conditions
occur. The Survey Meter has an audio alarm that can be set by the user. Two
9 volt batteries, located in the back of the Survey Meter, provide over 200 hours
of continuous operation. A 440 mg/cm2 phenolic shield is provided as a beta
shield. The shield also serves as an equilibrium thickness for photon
measurements & protects the Mylar window.
Intended Use
The 481 Ion Chamber Survey Meter is a hand-held, battery operated unit
designed to measure beta radiation above 100 keV and gamma and x-ray
radiation above 7 keV.

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Safety Information
A Warning identifies conditions and procedures that are dangerous to the user.
A Caution identifies conditions and procedures that can cause damage to the
Product or the equipment under test.
Table 1 is a list of symbols used on the product and in this manual.
Table 1. Symbols
Symbol Description Symbol Description
Hazardous voltage. Risk of
electric shock. Risk of Danger. Important information. See Manual.
DC (Direct Current) On/Off button

This product complies with the
WEEE Directive (2002/96/EC)
marking requirements. The affixed
label indicates that you must not
discard this electrical/electronic
product in domestic household
waste. Product Category: With
reference to the equipment types
in the WEEE Directive Annex I,
this product is classed as
category 9 "Monitoring and
Control Instrumentation" product.
Do not dispose of this product as
unsorted municipal waste. Go to
Fluke’s website for recycling
information.

This product contains a Lithium-ion
battery. Do not mix with solid waste
stream. Spent batteries should be
disposed of by a qualified recycler or
hazardous materials handler per
local regulations. Contact your
authorized Fluke Service Center for
recycling information.
Conforms to European Union
directives.
 Warning
To prevent possible electrical shock, fire, or personal injury:
•Read all safety information before you use the Product.
•Use the Product only as specified, or the protection
supplied by the Product can be compromised.
•Remove the batteries if the Product is not used for an
extended period of time, or if stored in temperatures above
50 °C. If the batteries are not removed, battery leakage can
damage the Product.
•The battery door must be closed and locked before you
operate the Product.

Ion Chamber Survey Meter
Safety Information
3
•Replace the batteries when the low battery indicator shows
to prevent incorrect measurements.
•Comply with local and national safety codes. Use personal
protective equipment.
•Carefully read all instructions.
•Do not touch voltages > 30 V ac rms, 42 V ac peak, or
60 V dc.
•Do not use the Product around explosive gas, vapor, or in
damp or wet environments.
•Do not use and disable the Product if it is damaged.
•Do not use the Product if it operates incorrectly.
•Examine the case before you use the Product. Look for
cracks or missing plastic.
•Use this Product indoors only.
•Remove all accessories before the battery door is opened.
•Each person who uses a product that senses and measures
ionizing radiation must:
oBe approved to do work where there is radiation
oObey all applicable safety procedures and
regulations
oBe approved to correctly interpret the indications
on the product
The user of this Product must read and strictly obey the
instructions and precautions contained in the manuals. If
you do not obey the instructions and precautions, there is
a risk of injury. If you do not obey the instructions and
precautions there is a risk that the Product will show
incorrect indications. Before each use, do a battery check
and other preoperational checks to make sure that the
Product operates correctly.

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gpl01.bmp
Figure 1. Fluke 481 Ion Chamber Survey Meter

Ion Chamber Survey Meter
Features
5
Features
The following sections describe the features of the Survey Meter.
Overrange Rate
If the instantaneous radiation rate measured by the Survey Meter exceeds
50 R/h (0.5 Sv/h), the 'R' in R/h or the 'Sv' in Sv/h displayed will blink to notify the
user that the radiation field exceeds the measuring capability of the Survey
Meter. Also, a potential error in the integrated radiation value may exist due to
this condition. The blinking will stop when the integrated value is cleared.
Low Battery Indicator
There are about 6 hours of operation remaining when the LOW BATTERY
indicator first becomes visible. When the LOW BATTERY indicator blinks, there
is less than 1 hour of operation remaining. These times are for two batteries
installed and from the first occurrences of these indications. If the Survey Meter
is turned off during a low battery condition, the batteries will recover somewhat,
but time of operation remaining will be less.
Audio Alarm
The audio alarm set points are set using the RS-232 COM port connected to a
computer along with the associated software. The audio alarm set point is set in
increments of 1 % full scale. That is from 1 % to 100 % of full scale. The “A”
command in the menu allows access to the scale and percent set point. The
alarm will sound when readings reach or exceed the set point.
Integrate Mode
The Integrate Mode allows the Survey Meter to display the integrated exposure.
Exposures are accumulated up to 999 R (9.99 Sv).
Freeze Mode
The Freeze Mode will move a “bar” on the bar graph display to show the user the
peak value, and will lock on the maximum range. The Survey Meter will continue
to read and display current readings.
Auto-On Backlight
The Survey Meter is equipped with a backlight which automatically turns on when
ambient light drops below a predetermined level. The backlight will turn off when
the ambient light exceeds the predetermined level, which is factory set.

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Specifications
Radiation Detected ............................................... Beta above 100 keV, gamma above 7 keV
Operating Ranges ................................................. 481: 0 mR/h to 5 mR/h, 0 mR/h to 50 mR/h, 0 mR/h to 500 mR/h, 0 R/h
to 5 R/h, 0 R/h to 50 R/h
481-DE-SI: 0 μSv/h to 50 μSv/h, 0 μSv/h to 500 μSv/h, 0 mSv/h to
5 mSv/h, 0 mSv/h to 50 mSv/h, 0 mSv/h to 500 mSv/h
Accuracy................................................................ ±10 % of reading between 10 % and 100 % of full-scale indication on
any range, exclusive of energy response (Calibration source is 137 Cs)
Detector ................................................................. 349 cc volume air ionization chamber; phenolic chamber wall
246 mg/cm2. Chamber window is composed of 6.6 mg/cm2 Mylar. A
coating of graphite has been applied to the walls to make them
conductive. The collection potential is -63 Volts. The Chamber is
vented through the desiccant
481-DE-SI: In order to achieve energy response consistent with
measurements of H*(10) as required by ICRU report 47, aluminum has
been added to the back wall, 38 % of the side wall area, and to the
beta slide. With the Beta Shield open, the 481 can measure skin dose
at H*(0.07), and Deep Dose H*(10) with the Beta shield closed.
Warm-Up Time....................................................... Less than one minute for initial operation
Response Time ..................................................... Time measured from 10 % to 90 % of final value for a step
increase/decrease in radiation rate such that a range change does not
occur:
481: 0 mR/h to 5 mR/h, range: 8 seconds. 0 mR/h to 50 mR/h, range:
2.5 seconds. 0 mR/h to 500 mR/h range: 2 seconds. 0 R/h to 5 R/h,
range: 2 seconds. 0 R/h to 50 R/h, range: 2 seconds
481-DE-SI: 0 μSv/h to 50 μSv/h, range: 8 seconds. 0 μSv/h to
500 μSv/h, range: 2.5 seconds. 0 mSv/h to 5 mSv/h, range: 2 seconds.
0 mSv/h to 50 mSv/h, range: 2 seconds. 0 mSv/h to 500 mSv/h range:
2 seconds
NOTE: Instantaneous exposure rate is limited to 50 R/h (0.5 Sv/h),
including but not limited to a pulsed field.
Precision................................................................ Within 10 % of reading
Readout.................................................................. Liquid Crystal Display: Contains an analog bar graph with a permanent
scale on the display and a 2½ digit display. Analog Display: The bar
graph consists of 100 segments, 2½ inches long; the scale has five
major divisions; the appropriate value for the operating range of the
instrument will appear below the scale. Digital Display: The digital
display is 2½ digits followed by a significant zero digit depending on
the operating range of the instrument. The leading ½ digit is blank, or a
“1” or a “0” for clarity. Units of measure appear to the right of the digital
display. Appropriate multipliers also appear on the display units: As
indicated under Range, programmable in R/h or Sv/h
External Controls .................................................. ON/OFF button, MODE button.
Automatic Features .............................................. Ranging and zeroing are fully automatic.
Environmental ....................................................... Operating Temperature Range: -20 °C to 50 °C
Relative Humidity Range: 0 % to 95 % non-condensing
Geotropism: less than 1 %
Altitude: 2000 m
For Indoor use

Ion Chamber Survey Meter
Specifications
7
Dimensions (L x W x H) ........................................ 8⅝in x 4½ in x 8 in (21.6 cm x 11.3 cm x 20 cm)
Weight .................................................................... Approximately 2 lb, 9 oz (1.16 kg)
Batteries................................................................. Two 9 volt batteries (NEDA 1604A or 6LR61 or 6AM6) provide over
200 hours continuous operation. Three lithium cells provide chamber
bias voltage of 63 V (10 year life expectancy)
Audio Alarm........................................................... Set through communication programs. Setting at 1 % increments, 1 %
to 100 % full scale
Temperature Sensor ............................................. A temperature sensor in the 481-DE-SI is used to adjust for offset drift
due to temperature. Readings are not corrected for changes in air
density due to pressure and temperature
Check Source ........................................................ Model 450UCS (item number 3267644), allows user to check for
proper instrument operation. Gives a nominal reading of 0.4 mR/h
(4 μSv/h)
IP Rating ................................................................ IEC 60529: IP40
Safety ..................................................................... IEC 61010-1: Pollution Degree 2
Electromagnetic Environment ............................. IEC 61326-1: Portable
Emissions Classification...................................... IEC CISPR 11: Group 1, Class A.
Group 1 ISM equipment: group 1 contains all ISM equipment in which
there is intentionally generated and/or used conductively coupled
radio-frequency energy which is necessary for the internal functioning
of the equipment itself. Class A equipment is equipment suitable for
use in all establishments other than domestic and those directly
connected to a low voltage power-supply network which supplies
buildings used for domestic purposes.
Model 481B-DE-SI Typical Energy Dependence
Dose equivalent units were determined using conversion coefficients at H*(10), found in ICRU 47,
April, 1992.
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
00001000100101
Energy (keV)
Indicated / Actual
Side
Slide - Closed
Slide - Open
gpl02.eps

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Model 481B Typical Energy Dependence
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
00001000100101
Effective (keV)
Indicated/Actual
Side
Slide - Closed
Slide - Open
gpl03.eps
Receiving Inspection
Upon receipt of the Survey Meter:
1. Check the shipping cartons(s) and their contents for in-shipment damage.
2. Check that all items listed on the packing slip are present and in good
condition.
If damage is evident, make a claim with the carrier and contact Fluke
immediately. If items are missing, contact Fluke. See the How to Contact Fluke
section in this manual.

Ion Chamber Survey Meter
Operation
9
Operation
The following sections describe the operation of the Survey Meter.
 Warning
To prevent possible electrical shock, fire, or personal injury, do
not put metal objects into connectors.
External Controls
There are two external controls on the Survey Meter: an ON/OFF button and a
MODE button.
ON/OFF Button
Press the ON/OFF button to turn on the Survey Meter. All the elements in the
display turn on and the microprocessor runs through an initialization procedure.
Part of the procedure includes reading the calibration coefficients stored in
EEPROM. If an EEPROM read error occurs, an error code (E1) displays at
power-on and unity calibration coefficients are used.
The bar graph and digital display will show a reading that decreases as the
Survey Meter stabilizes. The initial reading usually starts in the 50 R/h
(50 mSv/h) range and decreases through the lower ranges to a reading of less
than 0.5 mR/h (5 μSv/h) within 40 seconds. When the elements in the display
turn off, with the exception of those necessary for normal operation, the user can
begin the measurement process.
Note
Background fluctuations may occur (less than 0.5 mR/h (5
μ Sv/h))
returning to the original reading typically in less than 3 seconds.
Mode Button
To configure the MODE button to the opposite function without the RS-232
connection, use the following procedure:
1. Turn off the Survey Meter.
2. Press the MODE button.
3. Turn on the Survey Meter while continuing to press the MODE button.
4. Release the MODE button when the display is in the “all elements on”
condition.
5. Use the MODE button to toggle the Survey Meter between the rate mode and
the newly selected Freeze or Integrate mode.

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Freeze Mode
When configured to select the Freeze mode, the MODE button acts as a toggle
switch. Press the button until FREEZE appears on the display. Operation in the
Freeze mode gives the user a constant reference of the highest exposure rate
obtained from the time the freeze function is initialized. The highest reading will
appear as a single bar on the bar graph. The current reading will continue to be
displayed on the digital display and the bar graph. If a measurement is obtained
which exceeds the freeze bar reading, the freeze bar will move to the higher
measurement point. The operating range of the Survey Meter remains locked on
the highest range attained during the Freeze mode so that the scale and the
multiplier remain the same.
For example, assume the scale units appear as 10, 20, 30, 40, 50, and the
freeze bar is at 47 mR/h on the bar graph. If the Survey Meter then measures a
radiation field of 120 mR/h, the scale units will change to 100, 200, 300, 400,
500, and the freeze bar appears on the graph at 120 mR/h. If the Survey Meter
measurement goes below 100 mR/h, the units on the scale will not change until
the Survey Meter is taken out of the Freeze mode. However, the digital display
continues to show the current reading. The Survey Meter will operate in the
Freeze mode until the user toggles the MODE button to return to the normal
operating mode.
Note
If a measurement is obtained which causes a range change higher
than the alarm set point range, the alarm will sound and continue to
sound until the Freeze mode is disabled.
Integrate Mode
The Integrate mode is operational 30 seconds after the Survey Meter is turned
on and all of the time after that. However the integrated exposure can only be
displayed when the MODE button has been configured as a toggle to display
exposure rate/integrated exposure. If the MODE button is pressed within the
30 second initialization period of the Survey Meter, the display will read “0.”
When integration starts, “0.0 μR (0.00 μSv)” displays. Toggle MODE to read
exposure rate as required.
To reset the integration display, toggle the display from the Rate mode to the
Integrate mode. Keep the MODE button pressed for about 5 seconds. The
display will clear, and then read “0.0 μR (0.00 μSv).” Exposures are accumulated
up to 999 R (9.99 Sv).

Ion Chamber Survey Meter
Operation
11
Self-Test
When the Survey Meter is first turned on, it runs through a functional self-test
procedure. During this self-test, the firmware version of the Survey Meter
displays, along with the HI or LO chamber bias.
Warning
For safe operation and maintenance of the product, note the
chamber bias from the self-test. If chamber bias is LO, the
Product cannot measure high radiation rates accurately. The
Product requires service, contact Fluke.
If the Survey Meter passes the self-test, it goes into the normal operating mode.
If the Survey Meter fails the self-test it remains locked with the firmware revision
displayed. Contact Fluke for corrective action. See the How to Contact Fluke
section in this manual.
Installation
The Survey Meter periodically tests for mark signal at its RS-232 port. When an
RS-232 signal is detected, the Survey Meter sends test signals using its sending
device and, if RS-232 is present and operational, the Survey Meter will enter into
the communications mode. The Survey Meter display clears and the letters “CO”
display as an indication that the Survey Meter is in the communications mode.
The Survey Meter is compatible with a CRT or printing terminal having a
standard RS 232 connector and a 1200-baud rate. A computer with a modem or
terminal emulator can be used in place of the terminal. Set up the terminal or
computer for 1200 baud, 7 data bits, no parity bit, and 1 stop bit.
1. Connect the 9-pin female connector to an active communication serial port.
2. When “CO” appears on the Survey Meter display, press the computer or
terminal space bar twice.
If the Survey Meter displays the “CO” message but there is no response at the
terminal after pressing the space bar twice, perform the following tests:
•Be sure that the Survey Meter and terminal are properly connected via the
RS-232 cable.
If there is still a problem, contact Fluke for further instructions. See the How to
Contact Fluke section in this manual.

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Operational check
Fluke recommends an operational check upon receipt of the Survey Meter and
before each use. Monitor the start sequence. These results indicate the Survey
Meter is operating correctly:
•There are no error messages in the startup sequence.
•The display does not freeze (showing only the firmware number).
•The Survey Meter gets to the background level within 2 minutes.
Optional Check Source Use
Warning
To prevent personal injury, use care in the handling and
storage of the check source. The check source contains
radioactive materials used for the verification of the Product
operation.
For more testing use the check source Model 450UCS (Fluke part number:
3267644), a radioactive button source that provides a nominal reading of
0.4 mR/h (4 μSv/h).
To check the Survey Meter, do the following:
1. Turn on and initialize the Survey Meter.
2. After the self-test completes, wait for 2 minutes.
3. Open the beta shield.
4. Place the check source flat against the end window.
5. Check for a nominal reading of 0.4 mR/h (4 μSv/h).