Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140

AMS285-1.2/AMS385-1.2

Micropower Thermocouple Cold Junction Compensator

+

LM334

AMS385-1.2

R1

R2

ZERO ADJ

100k

1M

1%

5.1k

2k

1%

TC ADJ

500

METER

MERCURY

CELL

1.345V

+

-

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)

(

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

408

953

Ω

12.17

11.17

S

6.4

63.4

150

Ω

1.908

1.766

Typical supply current 50

µA

Precision 1

µµA to 1mA Current Sources

7

4

3

2

+

-

LM312

6

AMS385-1.2

R2

R1

100k

-30V

-1.5V TO -27V

C1

150pF

I

7

4

3

2

+

-

LM312

6

R2

R1

100k

30V

1.5V TO 27V

C1

150pF

I

AMS385-1.2