Fluke Biomedical 190I - Manual (Page 23)

Theory of Operation
Operational Considerations and Applications
3
3-3
Deadtime Effects
The deadtime correction is limited to a maximum multiplier of 3.7 above 10 6 counts per minute (cpm) 5.4
from 10 5 to 10 6 cpm, and 1.6 from 10 4 to 10 5 cpm. Larger correction factors are permitted at higher count
rates because of increased counting statistics. The display will indicate "OVER RANGE" if the deadtime
correction is greater than the values listed. This typically happens only on scale 6. In the event of an
overrange indication due to the deadtime the bar graph portion of the display continues to function and
may be used to observe increased or decreased radiation even though numerical values are not
displayed. The bargraph displays relative values in this mode.
Low Battery Indications
Once every 256 seconds the instrument checks the amount of energy remaining in the batteries. When
the values reach a threshold, the instrument simultaneously displays a LOW BATTERY message and
sounds the sounder for a minimum of one second. The amount of time remaining before the unit stops
operating depends on previous use of the instrument. If the instrument is used for longer continuous
periods of time, there will be a slower decrease in available battery life at the battery end point; if the
instrument is on for shorter periods of time, the battery fails more precipitously at the battery end point.
The display may prematurely indicate a low battery
if the count rate is high and/or the backlight and/or
Alarm are operational simultaneously.
Response Times
The response times stated in Specifications in Section 1 -Introduction apply to the bargraph display. Since
the digital data is updated only once each second, a filter is used to smooth the readings. There is
approximately two seconds additional response time (10-90% of change) for the digital display.
Range Changing
A hysteresis is built into the range changing of the 190I to prevent excessive range changing near a
range change threshold. In addition, internal readings above 10% of the current full scale are allowed for
one full second prior to down-scaling. Any reading above the current full scale will cause a range change
to the next higher scale.
NOTE