IM-174/PD Ion Chamber Survey Meters (ca. 1980s)

The IM-174 is a small high range survey meter employing an ionization chamber. Oddly enough, the IM-174 employs two logarithmic scales: the standard scale is 1 to 500 rad/hr, and a second scale, 0.1 to 10 rad/hr, which is activated when the “Check” switch is depressed. The models 174A and 174B (photos below left) only employ a single scale: 1 to 500 rad/hr. The earliest reference I have for the IM-174 is the 1966 version of the List of Military and Civil Defense Radiac Devices while the earliest reference for the IM-174A and 174B is the 1987 version of the list.

Range: 1-500 rad/hr

Size: ca. 6 1/2” x 4 1/2” x 4 1/2”

Battery: One 1 1/2 volt D cell

Weight: 3.75 pounds

Manufacturers: Landsverk (model IM-174), Jordan (model IM-174), Canadian Admiral (models IM-174A, B), Nucor (models IM-174A, B). The manufacturer of this particular example is not indicated.

This particular unit has an Army calibration sticker on it dated August 1990.

The IM-174A and 174B have two controls. One is an "OFF"—"SET" knob used to turn the instrument on and off and to zero the meter. The other control is a lever switch used to check the battery condition and to activate the zero adjust function.

Donated by Steven Buxton.

References

• Defense Atomic Support Agency, List of Military and Civil Defense Radiac Devices. DASA 1243 revised, 1966.
• Naval Electronic Systems Command List of Radiacs in the Navy Program P-9670-1, February 1975.
• Defense Nuclear Agency List of Military and Civil Defense Radiac Devices HQDNA (AR) 3M Revised, August 1987.