Model 3 Technical Manual Section 1
Ludlum Measurements, Inc. Page 1-1 April 2016
Introduction
he Model 3 is a portable radiation survey instrument with four linear
ranges used with exposure rate or cpm (counts per minute) meter
dials, or a combination of both exposure rate and count rate
(referred to as “combo”) meter face dials. The instrument features a
regulated high-voltage power supply, unimorph speaker with audio ON-OFF
capability, fast-slow meter response, meter reset button, and a six-position
switch for selecting battery check or scale multiples of ×0.1, ×1, ×10 and
×100. Each range multiplier has its own calibration potentiometer. The unit
body and meter housing are made of cast aluminum and the can is 0.23 cm
(0.090 in.) thick aluminum.
The audio provides a brief “click” for every radiation event detected. It also
provides a steady tone to warn the user of a low battery condition. This low
battery warning overrides the position of the AUD ON-OFF switch.
Any Geiger-Mueller (GM) detector offered by Ludlum Measurements will
operate with this unit as well as any scintillation type detector. The
instrument is typically set at 900 volts for GM tube operation. For special
requirements of GM or scintillation detectors, the instrument high voltage
may be adjusted from 400 to 1500 volts.
The unit is operated with two ˝
D˝ cell batteries for operation from -20 to 50
°C (-4 to 122°F). For instrument operation below 0 °C (32 °F), either very
fresh alkaline or rechargeable NiCd batteries should be used.
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