Campbell Scientific CR9000X Measurement and Control System - Manual (Page 114)

Section 3. CR9000X Measurement Details
This results in the following maximum integration times for the given Filter
orders (Filter order 1 has no limit as it does not require storing multiple
values):
Filter Order 2: 32,640 uSec Filter Order 4: 16,320 uSec
Filter Order 3: 21,792 uSec Filter Order 5: 13,056 uSec
The equations used to plot the frequency responses for Charts 3.2.2-1 & 3.2.2-2:
Eq. 3.2.4 Sinc Filter Order N:
( )
( )
N
Freq
Freq Sin
sponse lative
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
Ч
Ч
=
π
π
Re Re
C H A R T 3 .2 .2 -1
F R E Q U E N C Y R E S P O N S E O F S Y N C F IL T E R O R D E R S 1 - 5
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
1 .2
0 1 2 3 4 5 6
F R E Q U E N C Y
N O R M A L IZ E D T O (1 /IN T E G R A T IO N T IM E )
REL
RESPONSE
S y n c O r d e r 1
S y n c O r d e r 5
Chart 3.2.2-1 shows the frequency responses times for the Sinc filters available
for the CR9058E. As can be seen, the 1
st order Sinc filter does not filter out
the higher frequency components of the input signal. This could result in
higher frequency signals being aliased back to lower frequencies. While the
5th order Sinc filter does a fairly good job filtering out higher order
frequencies, the trade off is that it also attenuates the signal at lower
frequencies as can be seen in Chart 3.2.2-2.
These plots assume equal integration times for all filter orders,
so the 5
th order Sinc filter would require 5 times the measurement
time as the 1 st order Sinc filter.
NOTE
3-26