Model 14C Survey Meter
Ludlum Measurements, Inc. Page 1 July 2022
1. Introduction
he Model 14C is a rugged, portable survey instrument that operates on two standard "D"
cell alkaline batteries. The instrument features a regulated high voltage power supply set at
900 volts and provides five linear ranges for measurement from 0 to 2000 mR/hr.
The unit body is made of rugged cast aluminum. Operating features of the instrument include a
unimorph speaker, mounted to the instrument can with an audio ON/OFF switch, fast/slow meter
response switch, meter reset button, battery check button, and six-position switch for selecting scale
multiples of ×0.1, ×1, ×10, ×100, and ×1000. Each range multiplier has its own calibration
potentiometer.
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.
This instrument is set for 900-volt GM (Geiger Mueller) tube operation and is typically used with an
external, thin-wall GM tube or pancake GM tube; however, other external detectors are compatible
with this instrument. An internal energy-compensated, high-range detector is used for the ×1000
range only. The internal detector is active whenever the instrument is on and in a very high radiation
field and will drive the meter needle to full scale.
The unit is operated with two "D" cell alkaline batteries for operation from 0 °C (32 °F) to
approximately 65.6 °C (150 °F). For operation in temperatures below 0 °C (32 °F), either very fresh
alkaline batteries or rechargeable NiCd batteries should be used. Battery drain is typically 5-7 mA in
low radiation fields.
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