Model 6485 Picoammeter Instruction Manual Range, Units, Digits, Rate, and Filters 4-7
Programming example — rate
The following command sets the integration rate for all measurement ranges to 2 PLC:
CURR:NPLC 2 ' Set integration rate to 2 PLC.
Filters
Filtering stabilizes noisy measurements caused by noisy input signals. The Model 6485
uses two types of filters: median and digital. The displayed, stored or transmitted reading
is simply the result of the filtering processes. Note that both the median and digital filters
can be in effect at the same time.
With both filters enabled, the median filter operation is performed first. After the median
filter yields a reading, it is sent to the stack of the digital filter. Therefore, a filtered reading
will not be displayed until both filter operations are completed.
The settings for the filter are global. The MEDN key is used to control the median filter.
The AVG key is used to control the digital filter (press CONFIG and then the AVG key to
configure). When either the median or digital filter is enabled, the FILT annunciator is on.
Median filter
The median filter is used to determine the "middle-most" reading from a group of readings
that are arranged according to size. For example, assume the following readings:
20mA, 1mA, 3mA
The readings are rearranged in an ascending order as follows:
1mA, 3mA, 20mA
From the above readings, it is apparent that 3mA is the median (middle-most) reading.
The number of sample readings used for the median calculation is determined by the
selected rank (1 to 5) as follows:
Sample readings = (2 × R) + 1
where; R is the selected rank (1 to 5)
For example, a rank of 5 will use the last 11 readings to determine the median; (2 × 5) + 1
= 11. Each new reading replaces the oldest reading, and the median is then determined
from the updated sample of readings.
Median filter operation — The median filter operates as a moving type filter. For exam-
ple, if the median filter is configured to sample 11 readings (Rank 5), the first filtered read-
ing will be calculated (and displayed) after 11 readings are acquired and placed in its filter
stack. Each subsequent reading will then be added to the stack (oldest reading discarded)
and another median filter reading will be calculated and displayed. The median filter oper-
ation will reset (start over) whenever the Zero Check operation is performed or the range
is changed.
To Next Page
Loading...
