®

ISC300

8

excitation current. Four wire measurements avoid this prob-

lem by measuring the voltage generated across the RTD on

a second pair of wires. Very little current flows through the

voltmeter, therefore the lead resistance error contribution is

negligible. Three wire resistance measurements also avoid

lead length resistance errors.

In Figure 8:

FAULT CONDITIONS

The ISC300 can be configured to detect line or transducer

faults which may occur in a system. Figures 8 to 14 show

how the output of the ISC300 will reflect these various fault

conditions by giving corresponding out of range outputs.

Com 1

+In

–In

0V

–V

ISO

I

2

I

1

R

S

Output < +0.1V

FIGURE 10. R

Com 1

+In

–In

–V

ISO

–V

ISO

I

2

I

1

R

S

Output < –5.1V

FIGURE 11. +In Open Circuit.

Com 1

+In

–In

+V

ISO

–V

ISO

I

2

I

1

R

S

Output > +5.1V

FIGURE 12. –In Open Circuit.

FIGURE 8. Normal Operation.

Com 1

+In

–In

+V

ISO

–V

ISO

I

2

I

1

R

S

Output > +5.1V

FIGURE 9. R

Com 1

+In

–In

I

–V

ISO

I

2

I

1

R

S

Output = G • V

IN

T

1

T

2

T

3

I

(1)

(2)

(1) – (2)