User Manual

2 AN337REV1
AN337
For example, assume a 10(60)A Class 0.5 watt-hour meter using a 200 uΩ shunt as the current sensor. The
voltage on the CS5463 I-channel input (IIN±) with the starting current (I
st
=0.1%I
b
) will be 2 uV which is
well below the I-channel noise leve l. Therefore, if I
RMS
was used to decide the no-load co ndition, the meter
will not pass the no-load and starting tests. Even though the meter has lower than 2 uV noise level and pass-
es the no-load test, this application can not be used as a 5(60)A meter because the noise level is fixed within
the application, however the starting curre nt would be 50% lower.
In the next example, P
Active
is used as the variable.
Assume the following:
• A 5(60)A Class 0.5 watt-hour meter, AC gain calibrated, with inputs of U
n
and I
max
•P
Active
_Imax = 0.36 (decimal register value, same below) with inputs of U
n
and I
max
•P
Active
_Ib = 0.03 with inputs of U
n
and I
b
•P
Active
_Starting = 0.00003 with inputs of U
n
and starting current (Ist = 0.1 % I
b
)
Typically, the residual value in the P
Active
register P
Active
_Residual is less than 0.000002 (with 150 mVrms
on VIN± and no signal on IIN±, HPFs enabled, N = 4 000).
Because P
Active
_Starting >> P
Active
_Residual, the threshold can easily be selected between
P
Active
_Residual and P
Active
_Starting (a thresho ld of 0.00 001, for ex am ple) to allow the m eter pass the n o-
load and starting tests.
Furthermore, if the meter is well designed and has very low system noise, the threshold can be set even
lower (e.g. 0.000005) to allow much smaller starting current which is more welcomed by electric utilities.
The meter current dynamic range (I
max
/I
b
) can also be extended.
Contacting Cirrus Lo gic Support
For all product questions and inquiries contact a Cirrus Logic Sales Representative.
To find one nearest you go to http://www.cirrus.com
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