AEZ 801 / 802
Measurement filtering
At a Glance
Mathematical formula
The system uses first order filtering.
The filtering coefficient can be modified (See Modification of the Filtering Value,
p. 247) from the PL7 screen or via the program.
The mathematical formula used is as follows :
Mesf n = α × ( – 1 ) + ( 1 – α ) × Valb n with:
α = filter efficiency,
Mesf(n)=measurement filtered at moment n,
Mesf(n-1)=measurement filtered at moment n-1,
Valg(n)=gross value at moment n.
At configuration, the user selects the filter value from seven possible values (0 to 6).
This value can be changed, even when the application is in RUN mode.
Note: Filtering is inhibited in fast cycle mode.
Filter values The filter values are as follows:
Required efficiency
No filtering
Low filtering
Medium filtering 3
4
High filtering 5
6
0
1
2
Value to be selected
α
corresponding
0
0,750
0,875
0,937
0,969
0,984
0,992
Filter response time
Cut-off frequency
(Hz)
0
111 ms
240 ms
-
1,431
0,664
496 ms
1,01s
2.03 s
4.08 ms
0,321
0,158
0,078
0,039
TLX DS 37 PL7 xxE
187
AEZ 801 / 802
Filtering and cycle time
The module continues its acquisitions and therefore its filtering calculations regardless of the cycle time of the application task.
For example:
If the cycle of the MAST task is 120 ms (module used in normal cycle), the module will have taken into account three or four new gross values per channel, before the
MAST task reads the measurement value.
Illustration:
120 ms
Start of cycle Start of cycle
MAST task cycle
Measurement acknowledgement
Measurement acknowledgement
Available measurement
Available measurement
Available measurement
Available measurement
Available measurement
Calculation Calculation Calculation Calculation Calculation
Filtering
Module cycle
Channel n gross value
32 ms
Channel n gross value
32 ms
Channel n gross value
32 ms
Channel n gross value
32 ms
Channel n gross value
If the cycle of the MAST task is 10 ms, the module will only provide a new value every three or four cycles of the MAST task.
188
TLX DS 37 PL7 xxE
AEZ 801 / 802
Illustration:
10 ms
Available measurement
Available measurement
Available measurement
Available measurement
Available measurement
MAST task cycle
Measurement acknowledgement
Calculation Calculation Calculation Calculation Calculation
Filtering
Module cycle
Channel n gross value
32 ms
Channel n gross value
32 ms
Channel n gross value
32 ms
Channel n gross value
32 ms
Channel n gross value
TLX DS 37 PL7 xxE
189
