5.2.2 Noise reduction
The digitized signals read from ADCs have additional noise which must be
removed. This low frequency noise correlates largely with the local AC current
frequency
Table 5.1: Channel groupings used for common mode noise rejection.
GROUP
|
ADC
CHANNELS
|
A
|
1,2,3,4
|
B
|
5,6,7,9,10
|
C
|
11,12,13,14,15,16
|
D
|
17,19,20,21,21
|
E
|
23,24,25,26,27,28
|
F
|
29,30,31,32
|
G
|
33,34,36,37
|
H
|
38,39,40
|
I
|
41,42,43,44
|
PV_A
|
1,2,3
|
PV_B
|
4,5,6,7
|
PV_C
|
8,9,10,11
|
PV_D
|
12,13,14
|
PV_E
|
15,16
|
(50
Hz), though other sources contribute. This noise is called common mode
noise and is common to all channels. Certain groups of channels demonstrated a
higher degree of correlation and were therefore grouped together for the
purposes of noise reduction. The groupings were determined by the widths of the
histograms described in section 5.2.1. Table 5.1 lists the groupings.