PCM-2 Manual.pdf - Voss Associates

Alpha & Beta RDAs
Alpha & Beta
Sensitivities
RDA Confidence
Count Time
Sigma Factor
Background
Sigma Factor
Alpha & Beta
Sum Zone Alarm
Alpha & Beta
Sum Channel Alarm
These are the Reliably Detectable Activities used to compute alarm setpoints for
the alpha and beta channels. Values entered are copied to all alpha and beta
detector channels; individual channel RDAs may later be changed in the Detector
Parameters screen.
A ratio above and below the mean of background counts beyond which a
single detector's background is determined to be indicative of a detector failure.
The default value is 0.5 for the beta channels, meaning that a detector with more
than twice or less than half as many counts as the system average is considered
suspect. Note that because the size, location and orientation of a detector affects
its background counts, each detector has a Geometry Factor which is used to
compensate for these variables. The default alpha sensitvity factor is 0.10.
This is the probability of detecting contamination of the specified RDA. Possible
values are 50 %, 75 %, 90 %, 95 %, 99 % and 99.9 %. Refer to the manual section
on statistical algorithms for a detailed discussion of this parameter.
The time (in seconds) for which all channels of the PCM-2 will count.
A multiplier of the background count rate standard deviation which influences the
false alarm rate. Refer to the section on statistical algorithms.
If a background update count differs from the stored average background rate by
this many standard deviations, the new rate immediately replaces the old. If the
detector(s) on which this occurs alarmed on the last measurement, they are
assumed to be contaminated.
A sum zone is a user defined group of two to four detectors which are grouped
together to enhance the monitor's ability to detect contamination spread over an
area shared by several adjacent detectors. The alpha or beta sum zone alarm
setpoint defines the activity required within the sum zone area before a sum zone
alarm is triggered. Refer to the upcoming section or sum zone setup for more
information on sum zones.
A sum channel is a sum zone consisting of every channel in the monitor. The
alpha or beta sum channel alarm setpoint is the activity which must be present
within the entire monitor before the sum channel alarm is triggered.
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PCM2.MAN/ Rev A/April 1995