AN2299

Calibration principles and underlying theory

Rev2

7/26

P‘ measured active power;

U‘=U(1+

I‘=I(1+

Then, negleting the term

1.3

Accuracy and stability influence factors

Even in a digital measuring system, all components which have any influence on the system

accuracy and stability are located in the input analog section.

Generally, there are only a limited number of internal components which determine the

accuracy characteristics of the system:

●

voltage and current sensors

●

signal conditioning section

●

oscillator frequency

●

internal reference voltage source

●

analog to digital converters' gain

The components used must be of highest quality to reach the desired stability and linearity.

The circuit must be carefully designed to minimize any influences on these components

which could degrade short time repeatability, linearity or immunity.

Also external influences can affect the meter accuracy, such as:

●

●

influences of high frequency electrical and magnetic fields (EMC)

●

common mode voltage between inputs and to earth

●

influence of low frequency magnetic fields

●

measuring setup (wiring, earth connection ground loop)

●

influence of source (stability of U, I,

φ, signal quality)

●

long-time drift

●

humidity

Unwanted external influences must be minimized. This can be achieved by careful shielding

of the analog part or by compensating for the influences in hardware or software.

P'

UI

•

1

ε

U

ε

I

++

()

•φ δ

+

()

cos

•

=

Eq. 6