Mirion Technologies GEM-5 User Manual

Alarm Settings and Strategy
Gem-5 User’s Manual 287
This is given by:
Equation 26 Alarm Level Set Point
Efficiency)Bq(ityAlarmActiv)cps(ALS ×=
(26)
…where AlarmActivity(Bq) is the Alarm Activity (i.e. the facility release limit)
specified in the F2 – (Zone) Settings screen and Efficiency is the zone efficiency.
The Contaminated Trip Point (CTP) is the count rate above background at which the
detection zone is considered to be definitely measuring contamination in excess of
the Alarm Activity (release limit), even allowing for statistical counting error. The
CTP is calculated as follows:
Equation 27 Contaminated Trip Point
)s(T
)cps(R
)s(T
)cps(R)cps(ALS
K)cps(ALS)cps(CTP
b
b
m
b
1
+
+
×+=
β
(27)
The difference between CTP and ALS represents the statistical error in ALS and in
the background average R
b
. The term
1
K
β
, is a statistical term related to the
confidence of alarm.
The Alarm Trip Point (ATP) is the count rate above background at which the
detection zone is considered to be possibly measuring contamination in excess of the
Alarm Activity (release limit). Conversely, a count rate below the ATP is considered
definitely clean, even allowing for statistical counting error. The ATP is calculated
as follows:
Equation 28 Alarm Trip Point
)s(T
)cps(R
)s(T
)cps(R)cps(ALS
K)cps(ALS)cps(ATP
b
b
m
b
2
+
+
×−=
β
(28)
The ATP is the Alarm Level Set point (ALS) minus the statistical error in the ALS
and background average values. Thus the ATP is the alarm level that results in
reliably detecting contamination at exactly the level for which the facility is
monitoring, however readings between ATP and CTP represent potentially false
contaminated decisions.
In most cases, the Used Trip Point (UTP) is the higher of LLD and ATP. This can
result in false “Contaminated” results when the count rate is between the ATP and the
CTP. However there are two important exceptions that serve to postpone or reverse a
“Contaminated” result if the net count rate is between the ATP (“potentially
contaminated”) and the CTP (“definitely contaminated”) levels. These exceptions
occur when Extend Count If Contaminated is enabled.
When Extend Count If Contaminated is enabled, then the UTP is the higher of
LLD and CTP. A net rate between ATP and CTP will extend the count time by the

Mirion Technologies GEM-5 Specifications

General

Brand	Mirion Technologies
Model	GEM-5
Category	Monitor
Language	English