160
EL3000
CONTINUOUS GAS ANALYZERS | OI/EL3000-EN REV. D
… 11 QAL3 monitoring
Control cards
CUSUM Control Cards
CUSUM control cards allow the isolated determination of
accuracy and drift of the AMS at the zero point and reference
point.
Parameters to determine the precision
hs
hs = 6.90 s
2
AMS
Test value to detect loss of precision
ks
ks = 1.85 s
2
AMS
Constant used to calculate the preliminary
total for standard deviation
dt
Difference between the current device display of the AMS and
the reference value (observe the sign)
sp
Preliminary normalized sum of AMS standard deviations
st
Preliminary normalized sum of the AMS standard deviations at
time t
N(s)t
Number of device displays since the occurrence of a standard
deviation different than zero
Parameters to determine drift
hx
hx = 2.85 s
AMS
Test value to detect drift
kx
kx = 0.501 s
AMS
Constant for calculating the total amount of
positive and negative differences and
calculating the correction needed for the AMS
dt
Difference between the current device display of the AMS and
the reference value (observe the sign)
Sum(pos)p
Preliminary normalized total of the AMS positive drift
Sum(pos)t
Normalized total of the positive drift of the AMS at time t
N(pos)t
Number of device displays since a positive deviation occurred
Sum(neg)p
Preliminary normalized total of the negative drift of the AMS
Sum(neg)t
Normalized total of the negative drift of the AMS at time t
N(neg)t
Number of device displays since a negative deviation occurred
Test for acceptance of the precision (‘Decrease of Precision’)
st
less than or equal to
hs
for both zero point and end point
AMS is working in the control area,
carry out drift testing
st
greater than
hs
for zero point or end point
Determine the cause of the failure,
notify the manufacturer in case of
device defects (drift check not
necessary)
Drift check
Sum(pos)t
less than or equal to
hx
and
Sum(neg)t
less than or equal to
hx
for
both the zero point and the end point
AMS is working in the control area
Sum(pos)t
greater than
hx
or
sum(neg)t
larger than
hx
for zero point or end point
Measured value is out of the control
range (‘Out of Control’), perform re-
alignment of the AMS
Shewhart Control Cards
Shewhart control cards are used to determine the combined
accuracy and drift of the AMS.
The differences dt between the measured values and the set
values at the zero point and reference point are determined.
These differences must be less than or equal to standard
deviations s
AMS
multiplied by extension factor 2.
If the difference for a measured value is greater, the measured
value is marked with a status ‘Out of Control’ (outside the
control range).
