Parker Hannifin Corporation – UTS User Manual
8
UTS Filtering Description
The UTS has several different filtering options which are described below. Refer to Section 8.5 for examples on
how to adjust these filters.
FIR filter
The signal is first smoothed by a FIR filter. The FIR filter is a rolling average of the last
n
unfiltered
measurements, where
n
is the number of FIR samples configured by PGN 0xFFB5 (set output filter settings).
Increasing the number of FIR samples increases the signal dampening.
IIR filter
The IIR filter uses the resultant value of the FIR filter. The IIR filter is a weighted average of the current
measurement from the FIR filter and the previous result from the IIR filter. The current measurement from the
FIR filter is weighted by
x
%, where
x
is the IIR filter weight percent configured by PGN 0xFFB5 (set output filter
settings), and the previous result from the IIR filter is weighted by (100 -
x
) %. Decreasing the IIR filter weight
percent increases the signal dampening and reduces responsiveness. The IIR filter will reduce high frequency
noise.
Heavy IIR filter
In some applications additional filtering may be desired to further reduce larger spikes in the output signal. The
heavy IIR filter can be used to reduce larger spikes without burdening the rest of the signal with heavier
dampening. When a spike induces a tilt angle rate of change (in °/s) more than the heavy IIR rate limit
configured by PGN 0xFFB5 (set output filter settings) the heavy IIR filter weight percent is used in place of the
normal IIR filter weight percent in the IIR filter. The heavier filtering reduces the spike. Once the tilt angle rate of
change decreases below the heavy IIR rate limit the normal IIR filter weight percent is used again. In practice,
the heavy IIR filter weight percent should be a lesser value than the IIR filter weight percent.
Notes:
•
A positive offset adjustment value increases the zero-tilt reading (offset) while a negative value decreases
the zero-tilt reading.
•
The maximum number of FIR samples that can be averaged is 45 (0x2D).
•
The FIR samples, IIR filter weight percent and heavy IIR filter weight percent cannot be zero.
•
Setting the heavy IIR rate limit to the max value of 983.025 °/s (0xFFFF) disables the heavy IIR filter.
•
Setting the FIR samples to 1 and the IIR filter weight percent to 100% yields an unfiltered output.