8

preserve CMR. The table below shows the suggested val-

ues. Similar scaling can be used with the ICL7126 and

ICL7136.

The ultra-low bias current of the ICL7611 allows the use of

large value gain resistors, keeping meter current error under

driving amplifier. See Figure 14.

The 50k

Ω pot trims offsets in the devices whether internal or

external, so it can be used to set the size of the difference

interval. this also makes it useful for liquid level detection

(where there will be a measurable temperature difference).

See Figure 15.

The reference junction(s) should be in close thermal contact

with the AD590 case. V+ must be at least 4V, while ICL8069

current should be set at 1mA - 2mA. Calibration does not

ple types, adjust values to the appropriate Seebeck coeffi-

cient. See Figure 16.

SCALE

K

0.223 to 0.473

220

0.47

C

-0.25 to +1.0

220

0.1

F

-0.29 to +0.996

220

0.1

For all:

+15V

10k

Ω

1k

Ω

+

AD590

-

20k

Ω

44.2k

Ω

0.1%

ZERO SET

115k

Ω

118k

Ω

FULL-SCALE

ADJUST

100

Ω

10k

Ω

2.7315V

M

+100

µA

+

-

-

ICL7611

FIGURE 15. DIFFERENTIAL THERMOMETER

10k

Ω

+

NO. 1

-

V+

50k

Ω

5M

Ω

10k

Ω

+

-

+

-

741

V

-

(8V MIN)

NO. 2

V+

1

SEEBECK

COEFFICIENT = 40

TYPE K

+

-

ICL8069

1.235V

4.7

µF

40.2

Ω

V+

+

-

+

-

FIGURE 16. COLD JUNCTION COMPENSATION FOR TYPE K THERMOCOUPLE

AD590