®

XTR101

9

40

–

e

IN

e'

2

+

1mA

1mA

–

+

R

4

V

4

2mA

–

+

–

+

–

+

–

+

–

+

–

+

2mA

–

+

–

+

–

+

–

+

R

T

e'

2

R

T

e

IN

1mA

1mA

R

4

V

4

2mA

e'

2

R

4

V

4

e

IN

2mA

e

IN

2mA

2mA

e'

2

R

4

V

4

e

V

4

= 1mA X R

4

e'

(b) Suppressed Zero Range

e

V

4

= 1mA X R

4

e'

(a) Elevated Zero Range

e

IN

= (e'

2

–V

4

)

V

(c) Elevated Zero Range

e

IN

= (e'

2

+V

4

)

V

(d) Suppressed Zero Range

FIGURE 8. Elevation and Suppression Circuits.

APPLICATION INFORMATION

The small size, low offset voltage and drift, excellent linear-

ity, and internal precision current sources, make the XTR101

ideal for a variety of two-wire transmitter applications. It can

be used by OEMs producing different types of transducer

transmitter modules and by data acquisition systems manu-

facturers who gather transducer data. Current mode trans-

mission greatly reduces noise interference. The two-wire

nature of the device allows economical signal conditioning

at the transducer. Thus the XTR101 is, in general, very

suitable for individualized and special purpose applications.

EXAMPLE 1

RTD Transducer shown in Figure 9.

Given a process with temperature limits of +25

°C and

+150

°C, configure the XTR101 to measure the temperature

with a platinum RTD which produces 100

Ω at 0°C and

200

Ω at +266°C (obtained from standard RTD tables).

Transmit 4mA for +25

°C and 20mA for +150°C.

The sensitivity of the RTD is

∆R/∆T = 100Ω/266°C. When

excited with a 1mA current source for a 25

°C to 150°C range

(i.e., 125

°C span), the span of e

X 125

°C = 47mV = ∆e

From equation 1, R

=

= 123.3

Ω

Span adjustment (calibration) is accomplished by trimming

At +25

°C, e'

= 1mA [100

Ω +

X 25

°C]

= 1mA (109.4

Ω) = 109.4mV

In order to make the lower range limit of 25

°C correspond

to the output lower range limit of 4mA, the input circuitry

shown in Figure 9 is used.

=

= 109.4

Ω

At +25

°C, e'

At +150

°C, e'

= 1mA [100

Ω +(

X 150

°C)]

= 156.4mV

common-mode voltage, they may be ignored in computing

e

∆I

40

40

16mA/47mV – 0.016

266

°C

100Ω

1mA

109.4mV

1mA

V

4

0.3244

266

°C

100Ω

The +4V to +6V CMV

requirement is met.

– 0 +

20

15

10

5

0

Elevated

Zero

Range

Suppressed

Zero

Range

Span Adjust

e

FIGURE 7. Elevation and Suppression Graph.