Keithley 6220 Reference Manual page 189

Model 6220/6221 Reference Manual
Filter type
There are two averaging filter types: moving and repeating. These filter types are
shown in
Moving filter
Basic moving filter operation – For the moving filter, every delta reading yields a
filtered Delta reading. The moving filter uses a first-in, first-out memory stack. As a
new Delta reading is placed in the stack, the oldest delta reading is removed from
the stack, and a filtered reading is calculated.
When the averaging filter is enabled, the first A/D conversion is placed into the
stack and copied to the other locations in the memory stack to fill it. For example,
if filter count is 10, then the first A/D reading and nine copies are loaded into the
stack. The readings are averaged to yield the first reading.
Settled filtered readings will not occur until all the "copied" A/D readings are
purged out of the stack. For filter count 10, the first nine averaged readings will be
unsettled.
Figure
readings begin with the 10th averaged reading.
The Filter Settled status bit (B8) of the Operation Status Register indicates if the
reading is settled or not. The bit will set (1) when the first settled filtered reading
occurs. For details on status structure, see
Delta and Pulse Delta – As shown in
be used with Delta and Pulse Delta.
Keep in mind that when using the averaging filter, a settled filter reading is not
available until after the filter stack is filled. The filter count sets the filter stack size.
When Delta or Pulse Delta is started, the filter stack is allowed to fill before the
first filtered Delta or Pulse Delta reading is stored in the buffer. Therefore, the total
number of Delta or Pulse Delta cycles that are performed is calculated as follows:
Total Number of Cycles = Moving Filter Count + Cycle Count
Example – Assume the filter count for the moving average filter is set to 10 and
Delta is configured to perform 25 cycles (readings). When Delta is started, the fol-
lowing operations are performed:
1.
2.
NOTE
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Figure 6-1.
6-1A shows the moving filter process. For filter count 10, settled filtered
The asterisk (*) annunciator turns on and the first 10 Delta cycles fill the
stack of the moving average filter with Delta readings.
Bit B8 (Filter Settled) of the Operation Event Register sets to 1 to indicate
that the filter is settled. See
Up to this point, no readings have been stored in the
buffer yet.
Return to
Averaging Filter, Math, and Buffer
Section 11.
Table 6-1, the moving average filter can be
Section 11 for details on status registers.
Section 6 topics
6-3