481 Ion Chamber Survey Meter Operators Manual April 2011 © 2011 Fluke Corporation. All rights reserved. Specifications are subject to change without notice. All product names are trademarks of their respective companies.
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.
Table of Contents Title Page Introduction........................................................................................................ How to Contact Fluke ........................................................................................ Features.............................................................................................................. Overrange Rate.............................................................................................. Low Battery Indicator....
81 Operators Manual ii
Introduction The Model 481 Ion Chamber Survey Meters are hand-held, battery operated units designed to measure beta above 100 keV and gamma and x-ray radiation above 7 keV, using the latest CMOS and LCD technology. The 481 case is constructed of high strength ABS plastic. A gasket and desiccant pack seal moisture out of the unit and provides a cushion for the internal components. The readout consists of a 2 1/2-digit liquid crystal display and a 100 segment analog bar graph.
481 Operators Manual Figure 1. Fluke 481 Ion Chamber Survey Meter gpl01.bmp Features The following sections describe the features of the Survey Meter. Overrange Rate If the instantaneous radiation rate measured by the Model 481 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 instrument. Also, a potential error in the integrated radiation value may exist due to this condition.
Ion Chamber Survey Meter Specifications Integrate Mode The Integrate Mode allows the Model 481 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 unit will continue to read and display current readings.
481 Operators Manual Environment .......................................................... Operating Temperature Range: -20 °C to 50 ºC Relative Humidity Range: 0 to 95% non-condensing Geotropism: Less than 1% Dimensions............................................................ 8 5/8 (l) x 4 1/2 (w) x 8 in (h) (21.6 x 11.3 x 20 cm) Weight .................................................................... Approximately 2 lb, 9 oz (1.16 kg) Batteries......................................................
Ion Chamber Survey Meter Receiving Inspection Model 481B Typical Energy Dependence 1.2 1.1 1 Side Indicated/Actual 0.9 0.8 Slide - Closed 0.7 Slide - Open 0.6 0.5 0.4 0.3 0.2 10 100 1000 10000 Effective (keV) gpl03.eps Receiving Inspection Upon receipt of the unit: 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.
481 Operators Manual Mode Button To configure the MODE button to the opposite function without the RS-232 connection, use the following procedure: 1. Turn the unit off. 2. Press the MODE button. 3. Turn the unit on 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 instrument between the rate mode and the newly selected freeze or integrate mode.
Ion Chamber Survey Meter Theory of Operation W Warning If chamber bias is LO, the instrument can’t measure high radiation rates accurately. Service to the instrument is required. If the unit passes the self-test, it will go into the normal operating mode. If the unit fails the self-test it will remain locked with the firmware revision displayed. Contact Fluke for corrective action. See the How to Contact Fluke section in this manual.
481 Operators Manual W Caution The user is cautioned about indiscriminately opening and disassembling the instrument. The high impedance circuits of the ion chamber are easily contaminated with grease and dirt that produce electrical leakage. Complete Assembly/Disassembly instructions are available in the Maintenance Section of this manual.
Ion Chamber Survey Meter Maintenance minor divisions are worth 0.05, 0.5 or 5. The incremental nature of both the digital reading and the analog bar graph provide greater accuracy for reading in different portions of the scale. For example, on the 0-5 mR/h (0-50 μSv/h) range, with a digital reading of 2.0 and above, the analog bar graph can be read more accurately than the digital display. Below a digital reading of 2.0, the digital display is more accurate because it consists of three significant digits.
481 Operators Manual Storage If the unit is to be stored prior to use, pack it in the original container, if possible, and store in an environment free of corrosive materials, fluctuations in temperature and humidity, vibration or shock. The instrument should be stored with the two 9 Volt batteries removed. Prior to use, check the condition of the desiccant. A blue color indicates that the desiccant is good, while a pink color indicates the need to replace/regenerate.
Ion Chamber Survey Meter Maintenance 4. Remove screws holding phenolic chamber cover to the base. 5. Determine the conductive side of the replacement Mylar sheet using an ohmmeter. 6. Carefully, so as not to crinkle it, place the new Mylar on the top of the chamber, conductive side facing the chamber. Use adhesive to secure the Mylar to the phenolic chamber. 7. Electrically connect conductive side of Mylar to conductive side of chamber. 8. Any wrinkles in the Mylar may be removed with a hot air gun.
481 Operators Manual screws removed in step 2. 8. Replace the 9-volt batteries, being sure to observe proper polarity. Remove screws (4 places) Figure 3. Base of Unit gpl05.eps y out of Push vial assembly out of Figure 4. Desiccant Vial gpl06.eps Lithium Cell Replacement 1. Remove the 9-volt batteries to be sure that the instrument will remain off during the disassembly process. 2. Remove the 4 screws from the case top. 3.
Ion Chamber Survey Meter Maintenance 8. Replace the 9-volt batteries, being sure to observe proper polarity. Replaceable Parts Information Fluke maintains a complete inventory of all normal replaceable parts. To place an order, or to obtain information concerning replaceable parts, contact Fluke. See the How to Contact Fluke section in this manual. Table 2.
481 Operators Manual Note Install fresh batteries prior to performing any calibration on this instrument. Troubleshooting Self-Test Failure If the unit fails self-test, it will remain locked on the firmware revision number. See the How to Contact Fluke section. High Background Readings Remove desiccant and bake per the instructions in the Desiccant Regeneration section of this manual. After replacement, bake unit at 50 °C for 8 hours. Erratic Readings Check for broken ion chamber window or loose collector.
