Ludlum Measurements 12, Technical Manual

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Model 12 Technical Manual
Section 2
Ludlum Measurements, Inc. Page 2-5 July 2017
The dial shown below has three arcs: a counts per minute scale (cpm), a
linear mR/hr scale, and a non-linear mR/hr scale for the ×100 range
only. The meter face also has a
BAT TEST
position.
The top cpm scale is valid for the ×0.1, ×1, ×10, and the ×100 ranges. The
linear (middle) mR/hr scale is valid for the ×0.1, ×1, and ×10 ranges. The
non-linear mR/hr scale is valid for the ×100 range only. This meter face is
commonly referred to as a “combo” meter face since it has both count rate
(cpm) and exposure rate (mR/hr) arcs. Simpler meter faces may only have
a count rate or an exposure rate arc(s) like the previous meter faces shown.
A “combo” meter face is specifically designed for a particular detector. In
the example above, the 1.0 mR/hr mark on the middle arc lines up with
3.3 kcpm on the upper arc. The meter face in this example works with a
detector that receives 3.3 kcpm per mR/hr (the Ludlum Model 44-9
pancake detector.)
In the following picture, the needle is on the first tick mark past the 4
kcpm mark. Therefore, if the instrument selector switch is on the ×0.1
range, the reading is 4.2 kcpm (multiplied by) ×0.1 = 420 cpm.