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8March2012/version 7

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

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CASR series

Ampere-turns and amperes

The transducer is sensitive to the primary current linkage

Q

Q

Where

N

depending on the connection of the primary

jumpers)

Caution: As most applications will use the transducer with only

one single primary turn (

N

written in terms of primary current instead of current linkages.

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

current linkages are intended and applicable.

Transducer simplified model

The static model of the transducer at temperature

T

V

In which error =

V

With:

Q

:the input ampere-turns (At)

Please read above warning.

Q

:the maxi input ampere-turns that have

been applied to the transducer (At)

V

OUT

:the secondary voltage (V)

T

A

:the ambient temperature (°C)

V

OE

:the electrical offset voltage (V)

V

:the temperature variation of

V

temperature

T

G

:the sensitivity of the transducer (V/At)

ε

G

:the sensitivity error

ε

Pmax

Performance parameters definition

Sensitivity and linearity

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

is cycled from 0 to

I

I

The sensitivity G is defined as the slope of the linear regres-

sion line for a cycle between ±

I

The linearity error

ε

difference between the measured points and the linear

regression line, expressed in % of

I

Magnetic offset

The magnetic offset current

I

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

ferro-magnetic parts). It is included in the linearity figure but

can be measured individually.

It is measured using the following primary current cycle.

I

Figure 30:Current cycle used to measure magnetic and

electrical offset (transducer supplied)

0 A

t

t

Ip(3)

Ip(

3)

Gth

t

V

t

V

I

OUT

OUT

OM

1

2

)

(

)

(

2

1

⋅

−

=