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incremented until it reaches the maximum level set by FFST.IE if FFST = 10 then after a step change the fractional
part of a new reading is incremented as follows
1/1, 1/2, 1/3, 1/4, 1/5, 1/6.... 1/10, 1/10, 1/10
This allows the Filter to respond rapidly to a fast moving input signal.
With a step change, which does not exceed FFLV, the calculated new filtered value can be calculated as follows
New Filter Output value = Current Filter Output Value + ((Input Value - Current Filter Output Value) / FFST)
The time taken to reach 63% of a step change input (which is less than FFLV) is the frequency at which values are
passed to the dynamic filter, set in RATE, multiplied by FFST.
The table below gives an indication of the response to a step input less than FFLV.
Update Rate is 1/table value of RATE see Chapter 3 Output Rate Control.
% Of Final Value
63%
99%
99.9%
For example, If RATE is set to 7 = 100Hz = 0.01s and FFST is set to 30 then the time taken to reach a % of step
change value is as follows.
% Of Final Value
63%
1%
0.1%
The following table shows the number of updates x FFST and the error % New Filter Output value will differ from a
constant Input Value.
x FFST
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Remember that if the step change in mV/V is greater than the value set in FFLV then
New Filter Output value = New Input Value.
Micron Meters DCell & DSC User Manual
Time To settle
Update Rate * FFST
Update Rate * FFST * 5
Update Rate * FFST * 7
Time To settle
0.01 x 30 = 0.3 seconds
0.01 x 30 x 5 = 1.5 seconds
0.01 x 30 x 7 = 2.1 seconds
% Error
36.78794412
13.53352832
4.97870684
1.83156389
0.67379470
0.24787522
0.09118820
0.03354626
0.01234098
0.00453999
0.00167017
0.00061442
0.00022603
0.00008315
0.00003059
0.00001125
0.00000414
0.00000152
0.00000056
0.00000021
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