AN2299

Fast digital calibration procedure

Rev2

17/26

●

Sensor nominal value of sensitivity again must be known, for example:

–

following target values can be calculated:

Target RMS reading for given In:

Target RMS reading for given Vn:

Voltage divider output:

From which R1 resistor value is obtained:

3.3.4

Online Procedure

According to the used current sensor and the chosen algorithm, a component (resistor or

current sensor) of the value calculated through Eq. 16, Eq. 20, Eq. 24 or Eq. 28 respectively

must be mounted on the board.

To start online calibration procedure, the following has to be verified:

●

EM is connected into the calibration system and it is properly configured according to

the chosen application

●

EM calibrators parameters are preset to initial data

●

Target values of line signals are stable

When the system is connected and powered on, a certain number of readings of RMS

values must be performed.

Due to the fact that 0.4% of ripple is present in the measured RMS values, more than ten

readings of these values should be gathered each cycle (20ms at 50Hz) and average values

X

I

V

BG

1000

•

•

In

A

I

Ki

•

G

DF

•

G

INT

•

B

I

•

•

-------------------------------------------------------------------------

=

[mV/A]

Eq. 24

In

K

S

•

A

I

•

Ki

•

G

IN T

•

G

DF

•

B

I

•

V

BG

1000

•

--------------------------------------------------------------------------------------

=

Eq. 25

fB

V

•

B

I

•

D

UD

•

f

M

X

I

•

------------------------------------------

=

Eq. 26

V

DI V

X

V

V

BG

•

A

V

Kv

G

DF

•

B

V

•

•

-------------------------------------------------

=

Eq. 27

R1

R2

Vn

V

DI V

–

V

DIV

-----------------------

•

=

[

Ω]

Eq. 28