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

AMS9491

Centigrade Thermometer

Micropower* 10V Reference

AMS9491

R

R1

1k

V1

V2

LM334

90k

25k

27k

1.2k

2.3k

OUTPUT

1mV/° C

2.2k

1.5V†

Calibration

1. Adjust R1 so that V1 = temp at 1mV/

°K.

2. Adjust V2 to 273.2mV.

† I

µA to 150µA

150pF

AMS9491

3.5M

500k

22M

1M

7

4

6

3

2

-

+

V

I

Q

10V

LM4250C

8

≅ 20µA standby current

Micropower Thermocouple Cold Junction Compensator

+

LM334

AMS9491

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