This popular model uses a sensitive 2.5 x 2.5 cm (1 x 1 in.) NaI(Tl) detector with a sensitivity of 175 cpm/µR/hr. The analog meter includes a backlight, has five selectable ranges, a meter light, and includes a fast/slow response switch.
This instrument is nearly identical to the Model 19 (above) but incorporates a more sensitive gamma detector that sees 650 cpm/µR/hr. It also features dual alarms, four selectable ranges, and front-mounted alarm lamp.
Ludlum's most popular Model 3 survey meter coupled to an external 2.5 x 2.5 cm (1 x 1 in.) NaI(Tl) detector (Model 44-2) that enables the detector to reach areas that others may not attain. The detector has a sensitivity of 175 cpm/µR/hr.