Page 13/18

11July2018/Version 1

LEM reserves the right to carry out modifications on its transducers, in order to improve them, without prior notice

www.lem.com

LES series

Magnetic offset

The magnetic offset current I

O M is the consequence of a current

on the primary side (“memory effect” of the transducer’s

ferromagnetic parts). It is measured using the following primary

current cycle. I

O M depends on the current value IP1 (IP1 > IP M).

Figure 26: Current cycle used to measure magnetic and

electrical offset (transducer supplied)

(DC)

0 A

t1

t

t

Ip(3)

t2

Ip(

3)

I

P

I

P N

−I

P1

G

th

t

2

V

out

t

1

V

out

I

O M

1

·

2

)

(

)

(

−

=

Ampere-turns and amperes

The transducer is sensitive to the primary current linkage Θ

P

(also called ampere-turns).

Θ

P = NP⋅IP (At)

Where N

P is the number of primary turn (depending on

the connection of the primary jumpers)

Caution: As most applications will use the transducer with only

one single primary turn (N

P = 1), much of this datasheet is

written in terms of primary current instead of current linkages.

However, the ampere-turns (At) unit is used to emphasis that

current linkages are intended and applicable.

Transducer simplified model

The static model of the transducer at temperature T

A is:

I

S = G⋅ΘP + ε

In which ε =

I

O E + IO T (TA) + εG ⋅ΘP⋅G + εL (ΘP max)⋅ΘP max⋅G + TCG⋅(TA−25)⋅ΘP⋅G

With:

Θ

P = NP⋅IP

: primary current linkage (At)

Θ

P max

: max primary current linkage applied to

the transducer

I

S

: secondary current (A)

T

A

: ambient operating temperature (°C)

I

O E

: electrical offset current (A)

I

O T (TA)

: temperature variation of I

O at

temperature T

A (°C)

G

: sensitivity of the transducer (V/At)

TCG

: temperature coefficient of G

ε

G

: sensitivity error

ε

L(ΘP max)

: linearity error for Θ

P max

This model is valid for primary ampere-turns Θ

P between

−Θ

P max and +ΘP max only.

Sensitivity and linearity

To measure sensitivity and linearity, the primary current (DC) is

cycled from 0 to I

P, then to −IP and back to 0 (equally spaced

I

P/10 steps). The sensitivity G is defined as the slope of the

linear regression line for a cycle between ±I

P N.

The linearity error ε

L is the maximum positive or negative

difference between the measured points and the linear

regression line, expressed in % of I

P N.

Performance parameters definition