Campbell Scientific CR9000X Measurement and Control System - Manual (Page 115)

Section 3. CR9000X Measurement Details
C H A R T 3 .2 .2 -2
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 T H R O U G H 5
0 .9 1
0 .9 2
0 .9 3
0 .9 4
0 .9 5
0 .9 6
0 .9 7
0 .9 8
0 .9 9
1 .0 0
1 .0 1
0 .0 0 0 .0 1 0 .0 2 0 .0 3 0 .0 4 0 .0 5 0 .0 6 0 .0 7 0 .0 8 0 .0 9 0 .1 0
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 yn c _ o rd e r_ 1
S yn c _ o rd e r_ 2
S yn c _ o rd e r_ 3
S yn c _ o rd e r_ 4
S yn c _ o rd e r_ 5
3.2.3 CR9058E; Hard Setting the Filter Order
Rather than letting the CR9058E firmware select the filter order based on the
integration time and scan interval, the user can hard set the filter order that will
be used by the CR9058E. If the Integration time parameter is set = -1, the filter
order is set to 1. If the Integration parameter is set to -2, -3, -4, or -5, then the
Sinc filter is forced to the corresponding filter order, 2,3,4,or 5 and the
integration time is maximized for the selected filter order. The resulting
integration time for a Sinc filter of order 1 would be about five times the
integration time available for a Sinc filter of order 5. For Chart 3.2.2-1 and
Chart 3.2.2-2, we have set the total available time for integration to be 1
"Period". Given the same Scan Interval (AvailTime), we have approximated
that a Sinc filter order 2 would have an integration time of Period/2, filter order
3: Period/3, filter order 4: Period/4, and filter order 5 would have an
integration time of Period/5. While this is not exact, it is a good approximation
for integration periods greater than 1 mSec. The actual method for determining
the integration time will be covered later.
Chart 3.2.3-1 shows the signal attenuation traces plotted against the signal
frequency (normalized to 1/(Period)). As can be seen, the 5th order Sinc filter
does a far better job of filtering out higher order frequencies than the lower
order sinc filters.
3-27