6. Appendices
008-0738-00
Rev B
TMS 9250 Product User Manual
41
April 2012
© 2012 – Honeywell International Inc. All rights reserved
again. The number of steps set by FiltSteps determines the number of fractional steps
that are taken to increment the output value, according to the following series :
1 / 2, 1 / 3, 1 / 4, 1 / 5
….etc.
•
The output characteristic is therefore exponential and behaves in a predictable
manner.
•
To determine the settling time of the filter (the time taken to reach the Vo = Vi
condition), it is necessary to know both the filter update rate and the number of
fractional steps. The filter update rate is fixed at 1104 Hz in the version v1.38 software
and above.
•
The cut-off point (in Hz) is given by the following expression
Frequency (-3dB) =update rate / number of steps / 6.3.
•
Table 1 below provides a quick reference to determine the filter characteristic Note
that this filter operates only when the change in the input is below the threshold set by
FiltLevel
.
Filter Settling Time
The time required for the output to settle following a step change in input level is given by the
following table.
Table 1: Filter Settling Time
% of Final Value
Time to Settle
63 %
Filter Update Period * FiltSteps
99 %
Filter Update Period * FiltSteps *
5
99.9 %
Filter Update Period * FiltSteps *
7
Where the Filter Update Period is the period in seconds (1/f), fixed at 0.000906s for software
v1.38
AND
Where the change in input signal magnitude is
below
the threshold set by
FiltLevel.