STPM11_08 STMICROELECTRONICS [STMicroelectronics], STPM11_08 Datasheet - Page 34

• Manufacturer Part Number: STPM11_08
• Description: Single phase energy metering IC with pulsed output and digital calibration
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

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Figure 22. Active energy computation diagram
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Energy calculation algorithm
Inside the STPM1x the computing section of the measured active power uses a completely
new patented signal process approach. This approach allows the device to reach high
performances in terms of accuracy.
The signals, coming from the sensors, for the instantaneous voltage is:
v(t) = V•sin ωt; where V is the peak voltage and ω is related to the line frequency (see[1])
and the instantaneous current is:
i(t) = I • sin (ωt + ϕ); where I is the peak current, ω is related to the line frequency and ϕ is the
phase difference between voltage and current (see[2])
Active power
In the STPM1x, after the pre-conditioning and the A/D conversion, the digital voltage signal
(which is dynamically more stable with respect to the current signal) is processed by a
differentiate stage which transforms:
v(t) → v’(t) = dv/dt = V
The result, together with the pre-processed and digitalized current signal:
⋅
ω
⋅
cos tω − [Eq. 1 - see (5) in
Figure
6]