Datasheet

STPM01 Theory of operation
Doc ID 10853 Rev 8 49/60
Equation 21
The RMS voltage value is obtained as:
Equation 22
For the apparent power another value is produced:
Equation 23
Multiplying Equation 20: and Equation 23: , the apparent power is produced:
Equation 24
Rogowsky coil
In this case we have:
Equation 25
while V
RMS
is calculated as in Equation 22: .
The apparent power is simple calculated multiplying Equation 25: and Equation 22: .
The DSP then performs the integration of the computed powers into energies. These
integrators are implemented as up/down counters and they can rollover. 20-bit output buses
of the counters are assigned as most significant part of energy data records. It is a
responsibility of an application to read the counters at least every second not to miss any
rollover.
2
I
I
RMS
=
2
V
dt)t(v
T
1
V
T
0
2
RMS
==
∫
2
V
dt)t(v
T
1
T
0
2
ω⋅
=
′
∫
2
VI
2
V
2
I
S =
ω⋅
⋅
⋅ω
=
2
I
dt)t(i
T
1
I
T
0
2
RMS
=
′′
=
∫