®

IXR100

9

5. Control relative humidity to as high a value as practical

(50% recommended).

RTD APPLICATIONS

The IXR100 has been designed with RTD applications

specifically in mind. The following information provides

additional information for those applications.

TWO- AND THREE-WIRE CONNECTIONS

The IXR100 performs well with two-wire and three-wire

RTD connections commonly encountered in industrial moni-

toring and control.

In two-wire applications, the voltage drop between the RTD

but care must be taken that this voltage drop does not vary

with ambient conditions. Such variation will appear as an

apparent variation in the RTD resistance and therefore as a

change in measured temperature. Also, the linearity correc-

tion will interpret this change as a variation and attempt to

linearize both the actual RTD signal and the resistance

changes in the signal lines. For these reasons, the line

resistance between the RTD and the IXR100 should be

minimized by keeping line lengths short and/or using large-

gauge wires. This limitation does not apply for three-wire

connections.

In three-wire applications, shown in Figure 7, the RTD and

the RTD. This occurs because the currents through the three

wires are set up in opposing directions and cancel IR drops

in the RTD leads. The current sources are both modulated

equally, so that use of the linearity correction does not affect

the cancellation. This action is true so long as the three wires

are of the same length and gauge. Because most RTD leads

are twisted and bundled, this requirement is usually met with

no difficulty. Care must be taken that intermediate connec-

tions such as screw terminals do not violate this assumption

by introducing unequal line resistances.

RTD ZERO ELEVATION AND SUPPRESSION

The IXR100 may be operated in zero-elevated and zero-

used in increase-decrease applications by interchanging the

current sources are matched and are modulated equally, this

connection has no effect on IXR100 performance, especially

in three-wire applications.

OPEN CIRCUIT DETECTION

In some applications of the IXR100, the RTD will be located

remotely. In these cases, it is possible for open circuits to

develop. The IXR100 responds in the following manner to

breaks in each lead. The following connections refer to the

RTD connections shown in Figure 7.

TERMINAL OPEN

1

32mA

2

3.6mA

3

32mA

NOTE: (1) Approximate value.

FIGURE 7. Basic 3-Wire RTD Connection for Increase-Increase Action.

+

–

4

1

3

7

6

2

V

IN

+

–

IXR100

R

= 3.9k

Ω

CM

5

0.4mA

0.01µF

0.4mA

D

1

Three-wire Connection

RTD

1

3

2

9

8

R

LIN

1N4148

R

L

–

+

V

OUT

+V

S

4-20mA

28

18