STPM12 datasheet(32/43 Pages) STMICROELECTRONICS

Part #	STPM12

Description	Single phase energy metering IC with pulsed output and digital calibration

PDF	43 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

Logo

32 / 43 page

Energy calculation algorithm

STPM11/12/13/14

32/43

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 ωis related to the line frequency (see[1])

and the instantaneous current is:

i(t) = I • sin (

ωt + ϕ); where I is the peak current, ωis 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

⋅ ω⋅ cos tω−[Eq. 1 - see (5) in Figure 6]

The result, together with the pre-processed and digitalized current signal:

Figure 22.

Active energy computation diagram

STPM12 Datasheet(PDF) 32 Page - STMicroelectronics