8
Autoranging
When radiation levels increase in some modes over certain preset levels, the Inspector uses autoranging,
automatically changing to the X1000 scale. While in CPM or Total/Timer mode, whenever X1000 is shown
above the numeric display, multiply the displayed reading by 1000 to determine the radiation level. mR/hr,
µSv/hr, and CPS are not applicable.
Operating in Dose/Rate Modes
Caution: Be sure there is no obstruction between the detector window and the source being monitored/
surveyed. Avoid making measurements with the GM window facing the sun, as it could affect your readings.
When the mode switch is set to mR/hr and CPM or µSv/hr and CPS, the numeric display is updated every 3
seconds unless you are using the Timer mode. At low count rates, significant changes in the radiation level
displayed can take up to 30 seconds to stabilize.
For details, see Autoranging in this chapter.
CPM, CPS, and Total counts are the most direct methods of measurement.
mR/hr and µSv/hr are calculated using a conversion factor optimized for Cesium-137. This mode is less
accurate for radionuclides other than Cs-137, unless you have calibrated the Inspector for the specific
radionuclide you are surveying.
The most immediate indicators of the radiation level are the audio and count light.
Operating in Timer Mode
When the mode switch is set to Total/Timer, the numeric display is updated every second and totaling starts.
Taking a Timed Count
The Inspector can give you a total count for a timed period from 1 minute to 24 hours. The default setting is 10
minutes. A timed total count is useful for determining the average counts per minute over a longer period of
time. The number of counts detected by the Inspector varies from minute to minute due to the random nature
of radioactivity. When a count is taken over a longer period, the average count per minute is more accurate.
Taking an average allows you to detect low-level contamination or differences in background radiation due
to altitude or soil mineral content. For example, if one 10-minute average is 1 count per minute higher than
another 10-minute average, the increase is likely due to normal variation. But over 12 hours, a 1 count per
minute increase over the 12 hour background average may be statistically significant.
You can end a timed count by pressing the SET button while the remaining time is displayed.
Mode
Ranges as they are displayed
CPM
0 to 2,999 CPM
> 9,999
X1000
10.000 (10,000) CPM to 350 (230,000)PM
Total/Timer
0-9,999 counts
> 9,999
X1000
10.00 (10,000) to 9999 (9,999,000) counts
