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7.3 Auto-range parameters
Auto-range controls the following parameters:
Frequency:
This setting must be set to the frame frequency of the
measured sample. The range is 1 to 255 Hz. If a sample has a
higher frequency than that, set it such way that 1/frequency covers
multiple frames of the sample.
Frames:
The minimum number of frames that should be
measured. It means auto-ranging will have a minimum
measurement time of (1/frequency)
·
frames. Example: In case
frequency is 60Hz and frames is 3, the MSE will measure at least
3 frames at an integration time of 16.66ms. This would be equal to
measuring in non-auto-range with a fixed integration time of
16.66ms and averaging of 3.
Adjmin:
The adjmin parameter is very important. The higher this
level is set, the more stable the measurement becomes, but it also
slows down the measurement if set too high. That means, there is
a trade-off between speed and stability. It mainly affects the lower
grey scale levels. If these levels appear not stable, adjmin needs
to be increased. adjmin is set from 1-50, which means 1-50% of
the adjmax level. The latter one is fixed by Admesy.
Maximum integration time:
Although not being part of the auto-
ranging algorithm, this parameter is used when the auto-ranging
result exceeds this setting of integration time. When the grey
scales are low (grey scale 0 for example), the maximum
integration time setting can be used to allow only a maximum
measurement time. Of course this affects stability (longer
measurement is always more stable), but again this is a trade-off
for production environments to save on test time.
7.4 Auto-range in practice
When auto-ranging is set, the measurement settings (integration time and
averaging) are automatically adjusted. This takes a bit of time of course.
An initial measurement is done to determine the final settings of averaging
and integration time, based on the settings of frequency, frames and
adjmin.
The set integration time of the instrument will always be used as the first
value to try. If this setting results in a value between adjmin and adjmax,
no further actions are necessary and the speed is optimal.
When measuring a display we can measure random patterns, but mostly
known patterns are measured. Setting an integration time that is nearly
right, 1/frequency (Hz) is preferred, as it optimizes the speed for adjusting
the auto-ranging settings and thus provides optimal results.
The following chapters show examples of measuring random patterns
(2 cases) and a gamma curve. All cases are compared by setting a fixed
integration time and a feedback of the integration time (useful for gamma
measurement).
Tables 13 and 14 on the next pages show the measurement / integration
time and also show that measurement time is greatly affected by setting
wrong initial values.
For this test, a 20” TFT display (standard desktop
LCD) was used with black at 0.2 cd/m² and white at 187 cd/m² and a frame
rate of 60Hz. Settings for auto-ranging are:
Frequency = 60
Frames = 3
Adjmin = 5
Содержание MSE Series
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