AMS285-2.5/AMS385-2.5

Micropower Thermocouple Cold Junction Compensator

+

LM334

AMS385-2.5

R1

R2

ZERO ADJ

100k

1M

1%

18k

2k

1%

TC ADJ

500

METER

3V

LITHIUM

+

-

R

THERMOCOUPLE

+

-

COLD JUNCTION

ISO THERMAL

WITH LM334

Adjustment Procedure

1. Adjust TC ADJ pot until voltage across R1 equals Kelvin temperature

multiplied by the thermocouple Seebeck coefficient.

2. Adjust ZERO ADJ pot until voltage across R2 equals the thermocouple

Seebeck coefficient multiplied by 273.2.

Thermocouple

Seebeck

R1

R2

Voltage

Voltage

Type

Coefficient

(

Ω)

(

Ω) Across R1

Across R2

(mV/

°C)

@ 25

°C (mV)

(mV)

J

52.3

523

1.24k

15.60

14.32

T

42.8

432

1k

12.77

11.78

K

40.8

412

953

Ω

12.17

11.17

S

6.4

63.4

150

Ω

1.908

1.766

Typical supply current 50

µA

Precision 1

µA to 1mA Current Sources

7

4

3

2

+

-

LM312

6

AMS385-2.5

R2

R1

68k

-30V

-1.5V TO -27V

C1

150pF

I

7

4

3

2

+

-

LM312

6

R2

R1

68k

30V

1.5V TO 27V

C1

150pF

I

AMS385-2.5

Advanced Monolithic Systems, Inc.

www.advanced-monolithic.com

Phone (925) 443-0722

Fax (925) 443-0723