Fluke Biomedical 451B - Manual (Page 11)

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Introduction
The Model 451B Ion Chamber Survey Meter (the Survey Meter) is a hand-held,
battery operated meter designed to measure alpha above 7.5 MeV, beta above
100 keV, and gamma & 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
provides 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 twenty 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 Survey Meter is
measuring. The units of measurement show next to the 2 ½ digit display. LOW
BAT and FREEZE appear on the display when the product 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 451B 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.