AN2299

Calibration principles and underlying theory

Rev2

5/26

1

Calibration principles and underlying theory

1.1

Measuring principle of a digital energy measurement system

Modern digital energy measuring systems, such as STPM01, are usually constituted by an

analog section with high-resolution Analog/Digital converters (ADCs) and a digital section

with powerful Digital Signal Processors (DSPs) to perform the measurement of power and

energy together with a variety of secondary parameters. The main scheme of such a system

is indicated in Figure 1.

Figure 1.

Principle of a digital power and energy measurement system

The analog section consists of voltage and current paths for each phase, and a common

area with system DC reference voltage and the system time base.

Voltage and current paths include the following blocks:

●

sensors for voltage and current

●

signal conditioning (to optimize signals to match the required input level of the ADC)

●

ADC

Common section consists of the following elements:

●

system DC reference voltage

●

system time base, provided by a quartz crystal oscillator or by an internal RC oscillator

The reference voltages and sample clocks used for the different ADC in the voltage and

current paths are synchronized to these basic quantities.

U’(

ϕ

I’( )

ϕ

I’

Current path

DS

P

igital

ignal

rocessing

δ

I

Reference

voltage

U

REF

T

ANALOG SECTION

Time

base

Sample

u’

n

Correction

,

εδ

II

Sample

u

n

Sample

i’

n

Correction

εδ

UU

,

Sample

i

n

EEPROM

Correction

εδ ε δ

UU

I

I

,

, ,

f

P

∼

P, Q, S, PF

U, I, f,

∠

U(

ϕ

I( )

ϕ

I

U

DC

∑ ⋅

ui

nn

1

N

P =

n=1

N

u(t)

i(t)