Filter setting commands – fm, fl, ur – Flintec LDU 78.1 User Manual
Page 19
LDU 78.1 Technical Manual, Rev. 12 May 2011
Page 19 of 36
8.4. Filter Setting Commands – FM, FL, UR
A digital filter can be set which will eliminate most of the unwanted disturbances. The commands FM and FL
are used to define the digital filter settings, the command UR is used to define an averaging of up to 128
measurement values. Please note that these filters are positioned immediately after the A/D Converter and
therefore affect all aspects of the weighing operation.
8.4.1. FM Filter
Mode
This command defines the filter mode. Allowed settings are 0 (IIR filter) and 1 (FIR filter).
Master (PC / SPS) sends
Slave (LDU XX.X) responds
Meaning
FM
F+00001
Request: FM = 1 (FIR filter)
FM 0
OK
Setup: FM = 0 (IIR filter)
WP
OK
Setup saved
The digital IIR filter operates as 2
nd
order low pass filter and Gaussian characteristics. The attenuation is
40dB/decade (12 dB/octave).; compare to mode 0 of the below table
The digital FIR filter operates as lowpass filter; attenuation see mode 1 in the below table.
Default setting: 0 (IIR filter)
8.4.2. FL Filter
Settings
This command defines the filter cut-off frequency.
Master (PC / SPS) sends
Slave (LDU XX.X) responds
Meaning
FL
F+00003
Request: FL = 3
FL 1
OK
Setup: FL = 1
WP
OK
Setup saved
The permitted settings are from 0 and 8 (see below table
). The setting 0 disables the filter.
Default setting: 3.
Settings for IIR Filter (Mode 0)
FL
Settling time for 0,1%
accuracy (ms)
3 dB – corner
frequency (Hz)
Attenuation at 300 Hz
(dB)
Max. output rate*
(values/s)
0
unfiltered
**
600
1 55
18 57
600
2 122
8 78
600
3 242
4 96
600
4 322
3 104
600
5 482
2 114
600
6 963
1 132
600
7 1923
0,5 149
600
8 3847
0,25 164
600
* Output rate = 600/2
UR
values/s
** Anti-aliasing filter 17 Hz @60 dB/decade (18 dB/octave)
Settings for FIR Filter (Mode 1)
FL Settling time for
0,1% accuracy
(ms)
3 dB –
corner freq.
(Hz)
20 dB
Attenuation
(Hz)
40 dB
Attenuation
(Hz)
Attenuation
in stopband
(dB)
Stop-
band
(Hz)
Max. output
rate*
(values/s)
0
unfiltered
**
600
1 47
19,7 48
64
> 90
> 80
600
2 93
9,8 24
32
> 90
> 40
300
3 140
6,5 16
21
> 90
> 26
200
4 187
4,9 12
16
> 90
> 20
150
5 233
3,9 10
13
> 90
> 16
120
6 280
3,2 8
11
> 90
> 13
100
7 327
2,8 7
9
> 90
> 11
85,7
8 373
2,5 6
8
> 90
> 10
75
** Anti-aliasing filter 17 Hz @60 dB/decade (18 dB/octave)
Note:
In mode 1 the output rate will automatically adapte to the selected filter setting.