9

®

ISO124

FIGURE 6. Thermocouple Amplifier with Ground Loop Elimination, Cold Junction Compensation, and Up-scale Burn-out.

FIGURE 7. Isolated 4-20mA Instrument Loop. (RTD shown.)

R

CM

1k

Ω

RCV420

XTR105

R

G

R

Z

(1)

13

3

4

2

6

7

10

14

1

0.01µF

4-20mA

RTD

(PT100)

0.8mA

0.8mA

1.6mA

14

15

16

3

2

10

4

12

11

5, 13

15

16

2

1

Gnd

–V

on PWS740

+V

9

10

7

8

–V

+V

ISO124

V

OUT

0V - 5V

NOTE: (1) R

2

6

10.0V

4

REF102

INA114

or

INA128

+In

7

4

3

8

1

2

5

16

15

8

10

ISO124

7

V

OUT

9

6

–In

+15V

+15V

–15V

+15V –15V

ISA

TYPE

E

J

K

T

MATERIAL

Chromel

Constantan

Iron

Constantan

Chromel

Alumel

Copper

Constantan

SEEBACK

COEFFICIENT

(µV/°C)

58.5

50.2

39.4

38.0

R

2

(R

3.48k

Ω

4.12k

Ω

5.23k

Ω

5.49k

Ω

R

4

(R

56.2k

Ω

64.9k

Ω

80.6k

Ω

84.5k

Ω

+15V –15V

R

3

100

Ω

Ground Loop Through Conduit

NOTE: (1) –2.1mV/°C at 2.00µA.

R

1

27k

Ω

Isothermal

Block with

R

2

1M

Ω

R

5

50

Ω

R

G

R

4

R

6

100

Zero Adj

Thermocouple

2

1