Product specifications

R01AN0168ED0101 Rev. 01.01 41
Application Note
Chapter 7 Performing Zero Point Detection
(5) Setting up the Digital Filter of ZPD
The digital filter of the ZPD function of ISM has a maximum depth of 16
measurements. After each measurement phase, the digital filter compares the
amount of measurement results, which have been above the reference level,
against its filter
level. If the level is less than this amount, the digital filter
indicates a “one”, which is equal to a filtered signal above the reference level.
Like this, the digital filter works like an adjustable
integration function.
To achieve the best effectiveness of the filter with maximum adjustability, it is
recommendable to have at least so many sampling points of the filter during
the measurement window, that it is enough to use the full depth of the filter, if at
least one
Measurement Cycle is performed. Then, the variable integration can
be adjusted in the full range of the filter depth.
Thus, in our example, we are using a
Measurement Cycle, that allows us to
repeat 15 times within the measurement window. Like this, it is a remaining
option for us, either to use one
Measurement Cycle with 15 sampling points, or
to use more
Measurement Cycles with less sampling points of the filter.
Figure 7-6 Setting up the Digital Filter of ZPD
Every green bar is representing a measurement, where the voltage of the
signal was clearly above the reference level. Red bars are indicating
measurements, where the voltage of the signal was clearly below the
reference level. And the yellow bars are indicating measurements, where
some uncertainty exists.
If we now set the digital filter
depth to 15, level to a value between 1 and 3, the
result of this single
Measurement Cycle would be “one”, thus indicating that the
ZP is not yet reached. A digital filter level of 6 or higher would cause a result of
“zero” of the filter, because the amount of measurements above the level is not
enough. In this case, the filter would indicate that the ZP was reached.
Now, depending on the condition when this measurement was taken (ZP or not
ZP), the digital filter level can be set accordingly.
Indicator
Raster:
144 µs
Reference
Level:
450 mV