Cirrus Logic CS5480 - Manual (Page 24)

CS5480
24 DS980F3
5.6 Tamper Detection and Correction
In the 1V-1I-1N meter configuration mode, the CS5480
provides flexibility for the user and application program
to adjust the anti-tampering scheme automatically or
manually. Automatic channel selection is enabled by
default. For manual channel selection refer to section
5.6.1.2 Manual Channel Selection on page 25.
The CS5480 provides compensation for at least two
forms of meter tampering — current and voltage tam-
pering.
5.6.1 Anti-tampering on Current
In the 1V-1I-1N mode, current tampering is deterred by
an automatic or manual channel selection scheme. A
dedicated second neutral current input is provided in the
event that the primary current input is impaired by tam-
pering.
5.6.1.1 Automatic Channel Selection
Automatic channel selection is standard in the CS5480.
When tampering is detected, the CS5480 will automatical-
ly select the channel with the greater Px
AVG
or Ix
RMS
mag-
nitude as the contributor to the total power registers. Using
either Px
AVG
or Ix
RMS
magnitude depends on the setting
of the IVSP bit in the Config2 register.
To avoid repeated channel transitions at light load, the
Channel Select Minimum Amplitude (P
MIN
(IRMS
MIN
))
register sets a minimum level for automatic channel selec-
tion. When either P1
AVG
(I1
RMS
) or P2
AVG
(I2
RMS
) is
greater than P
MIN
(IRMS
MIN
), the CS5480 will enable au-
tomatic channel selection. Within the automatic selection
region, the Channel Select Level (Ichan
LEVEL
) register
sets a minimum difference that will allow an automatic
channel change. The channel select level provides hyster-
esis to prevent repeated channel transitions that would oc-
cur when the primary line current and neutral current are
nearly equal.
Figure 15 shows how the automatic channel selection is
performed. In this figure, the magnitudes of P1
AVG
and
P2
AVG
are used for automatic channel selection (IVSP
= 0) and Ichan
LEVEL
= 1.02.
• The P1
AVG
and P2
AVG
must meet the Channel
Select Minimum Amplitude (Ichan
LEVEL
). The
highest channel is active, P1
AVG
in this example.
• Even when the active channel (P1
AVG
) moves below
the previously lower channel (P2
AVG
), the channel
selection does not change.
• The new channel selection is only made when the
difference between P1
AVG
and P2
AVG
is greater than
2% x P1
AVG
or P2
AVG
> P1
AVG
x Ichan
LEVEL
(1.02).
Channel Select Level
( Ichan
LEVEL )
2% minimum difference
Channel Select Level
( Ichan
LEVEL )
2% minimum difference
Channel Select Minimum Amplitude
P
MIN ( IRMS
MIN )
P1
AVG
P2
AVG
1 2 3
Channel 1 - Remains Active Channel 2 - Active Channel 1 - Active
Automatic Channel
Selection Region
Disabled Automatic Channel
Selection Region
Figure 15. Automatic Channel Selection