Page 15/18

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

External reference voltage

If the Ref pin of the transducer is not used it could be either left unconnected or filtered according to the previous paragraph

“Reference

V

The Ref pin has two modes Ref IN and Ref OUT:

● In the Ref OUT mode the 2.5 V internal precision reference is used by the transducer as the reference point for bipolar

measurements; this internal reference is connected to the Ref pin of the transducer through a 680 Ohms resistor. it tolerates

sink or source currents up to ± 5 mA, but the 680 Ohms resistor prevents this current to exceed these limits.

● In the Ref IN mode, an external reference voltage is connected to the Ref pin; this voltage is specified in the range 0 to 4 V

and is directly used by the transducer as the reference point for measurements.

The external reference voltage Vref must be able:

- either to source a typical current of

680

5

.

2

−

Vref

- or to sink a typical current of

680

5

.

2

Vref

−

, the maximum value will be 3.68 mA typ. when Vref = 0 V.

The following graphs show how the measuring range of each transducer version depends on the external reference voltage

value Vref.

Upper limit : I

Upper limit : I

Upper limit : I

(Vref = 0 .. 1.29 V)

Lower limit : I

(Vref = 0 .. 4 V)

Lower limit : I

(Vref = 0 .. 3.7 V)

Lower limit : I

(Vref = 3.7 .. 4 V)

Application information (continued)

-50

-40

-30

-20

-10

0

10

20

30

40

50

0

1

2

3

4

CASR 6

-100

-80

-60

-40

-20

0

20

40

60

80

100

0

1

2

3

4

CASR 15