General Measurement Instructions; Limit Value Function; Measurements With Statistics; Memory Full - Trotec BB 20 Manual De Instrucciones

General measurement instructions

If the calibration has been performed carefully, all
subsequent measurements will lie within the guaran-
teed measuring tolerance . Strong magnetic fields in
the vicinity of generators or railway tracks with strong
current fields can affect the measured values . If the
statistics program is used for the determination of the
average value, it is advisable to place the probe se-
veral times against a typical measuring point . Wrong
measured values or outliers can be deleted immedi-
ately in the menu . The last value originates from the
statistical calculation and the guaranteed degrees of
tolerance of the measured value .
Layer thickness = X ±s ±µ
Example:
Measured values: 150 µm, 156 µm, 153 µm
average value: X = 153 µm
standard deviation: s = ±3 µm
Measurement inaccuracy: µ = ±(1% of measured va-
lue + 1 µm)
d = 153 ±3 ±(1.53 µm + 1 µm) = 153 ±5.5 µm

05 . LIMIt VALuE FuNCtION

Limit values can be entered at any time using the DI-
RECT function and a selected group memory, i .e . be-
fore, during and after a series of measurements . Such
limit values can serve a very practical purpose .
Each measured value that lies outside the preset tole-
rance limits is indicated by a warning sound:
H: the measured value lies above the upper limit value
(HI limit)
l: the measured value lies below the lower limit value
(LO limit)
The limit values can be defined on the basis of the menu .

06 . MEASurEMENtS WIth StAtIStICS

The measuring instrument calculates statistics on the
basis of 80 performed measurements (GRO1~GRO4
(group 1 - 4): a total of 400 measured values can be
stored) . Although no measured values can be stored
in direct mode, statistics can be calculated as for
GRO1~GRO4. The statistics determined in direct
G
Operating manual – layer thickness measuring instrument BB 20
mode are deleted if the working mode is changed or
if the measuring instrument is switched off . The follo-
wing statistical values are calculated:
NO .: Number of measured values in the working mode
AVG: Average value
Sdev .: Standard deviation
MAX: Maximum value
MIN: Minimum value
Statistical definitions
Average value (x)
The sum of the measurements divided by the number
of measurements .
Standard deviation (Sdev .): x = ∑ x / n
The standard deviation is a statistic that measures
how the sample is 'spread' around the average value .
The standard deviation increases as the spread inc-
reases . The standard deviation of a number set is the
square average value of the deviation S
The variance of a list is the square of the standard
deviation of the list, i .e . the average value of the
squares of the deviations of the numbers in the list
from their average value divided by the (number of
measurements-1).
Variance: S = ∑ ( x- x )
2
Standard deviation: S = √s
A value must be deleted immediately after an irre-
gular measurement or an outlier . See the 'delete'
function in the menu .

Memory full

If the memory is full in group mode, the statistics are
not updated . Measurements can continue to be per-
formed . If the memory is full, further measurements
are not adopted into the statistics . The message
"FULL" appears on the display in single measuring
mode . If the memory is full in DIRECT mode, the old
measurements are replaced by the new measure-
ments and the statistics are updated .
.
2
/ ( n - 1 )
2
2
B - 9