This window lets you select the number of voltage readings to be averaged
for each recorded Chart sample value. Averaging is useful for
eliminating background electrical noise, or other short-term variation that
may obscure long-term trends. It may also be used to obtain single
integrated readings from long intersample intervals. Some important
aspects of averaging:
When
Continuous chart scanning
option is selected (A-D menu; available
in Chart mode only), all channels are scanned sequentially and continually
throughout the sample interval. The Averaging window is not
available, and differences in the number of averaged readings between channels
are not possible. This mode provides a more continuous sampling of
each channel than in the 'normal' averaging mode, wherein each sample is
sampled for N averages before proceeding to the next channel. It differs
from the 'continuous averaging' option described below in that all
channels are scanned continuously, not just the last one.
As for the normal averaging mode, in continuous scanning mode, the
number of averaged readings per recorded sample depends on the number of
channels, the sample interval, and the speed of the computer and the A-D
converter. |
The number
of readings that can be averaged depends on the number of channels, the
sample rate, the speed of the computer, the absolute value of input voltages
(low voltages take slightly longer to read than high voltages), and the
conversion type used (power functions take longer to calculate than linear
or polynomial conversions). LabHelper offers a default maximal
averaging value, based on the sample interval and the number of channels
used (it assumes the same number of samples are averaged for all channels).
You can pick a different number by changing the values in the edit fields.
Remember that if you select a larger number you may slow LabHelper
down to the extent that it cannot keep up with the requested sampling rate.
If that happens, it will record data correctly and, when data are saved,
will calculate the actual sampling rate.
In Chart
mode, all of the channels can be set to can be set to make repeated readings
until the time of the next sample by switching the "Continuous averaging
(all channels)" button to 'on'. The program cycles through
all the channels in an endless loop until it is time for the next sample
(at that point all of the readings are averaged and stored). In this
mode at least one reading is always made.
In Chart
mode, the final channel can be set to continue making readings
until the time of the next sample by switching the "Continuous averaging
(last channel only)" button to 'on'. In this mode at least
one reading is always made.
NOTE: sample averaging is automatic if you have selected
Oscilloscope plus Chart mode. In this mode a voltage reading is made
from ALL channels when the oscilloscope reading is made. When the
sample interval for chart channels has elapsed, the stored readings for
the chart channels are averaged, plotted, and saved. Thus the number
of samples averaged for chart channels is roughly equal to the value:
chart sample interval / oscilloscope sample
interval
Use of this method simplifies calculations and allows the highest possible
oscilloscope sampling rate.
When you are satisfied, click the 'Selection OK' button.
|