Lord MicroStrain G-Link-200, User Manual

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G-Link
®
-200
User Manual
31
ii. Chunks
Windows can encompass thousands of samples, but a node can only operate on a finite number of
samples at a time, so the node chunks up data to run derived calculations. Chunk size is defined
below where
p
is the derived period,
d
is the burst duration, and is the maximum chunk size.
Maximum chunk size can change between nodes depending on how many resources are available
for derived calculations. The G-Link-200 has a max chunk size of 256 samples.
l
Continuous -
l
Burst-
Figure 20 - Derived Data Chunks
iii. Under-sampling
Under-sampling happens when there are not enough samples to accurately calculate a value for a
derived channel. The user should pick a window size that contains at least two periods of the lowest
rate input signal to be measured. The more information that can be included in the derived
calculation the more accurate the calculation will be.
For derived channels that use Fourier transforms on raw data, such as IPS, the chunk size will limit
the input frequency range rather than the window size. If the chunk size is at its maximum size the
only way to gain accuracy for lower frequencies is to reduce the sample rate.