THERMOCOUPLE COLD JUNCTION COMPENSATION

(compensation for grounded thermocouple)

LM135

LM235

LM335

R1

10k

Ω

4.7k

Ω

+15V

1N4568

R2

10

k

Ω

R3*

200k

Ω

1M

Ω

1%

Thermocouple

-15V

12k

Ω

71.5k

Ω

1%

1%

* Select R3 for proper thermocouple type

Adjustments : compensates for both sensor

and resistor tolerances.

1. Short 1N4568.

2. Adjust R1 for SEEBEC K coefficient times

ambient temperature (in degrees K) across

R3.

3. Short LM135 and adjust R2 for voltage

across R3 corresponding to thermocouple

type.

J

14.32mV

K

11.17mV

T

11.79mV

S

1.768mV

Thermo-

couple

R3

Seebeck

Coefficient

J

T

K

S

377

Ω

308

Ω

293

Ω

45.8

Ω

52.3

42.8

40.8

6.4

SINGLE POWER SUPPLY COLD JUNCTION COMPENSATION

LM135

LM235

LM335

R1

10k

Ω

10k

Ω

+15V

+15V

1N4568

200k

Ω

1M

Ω

R2

10

k

Ω

R4*

Output

Thermocouple

R3*

200k

Ω

* Select R3 and R4 for proper thermocouple

Adjustments :

1. Adjust R1 for the voltage across R3 equal

to the SEEBECK coeffi cient times ambient

temperature in degrees Kelvin.

2. Adjust R2 for voltage across R4 correspon-

ding to thermocouple.

J

14.32mV

K

11.17mV

T

11.79mV

S

1.768mV

Thermo-

couple

R3

R4

Seebeck

Coefficient

J

T

K

S

1.05k

Ω

856

Ω

816

Ω

128

Ω

365

Ω

315

Ω

300

Ω

46.3

Ω

52.3

42.8

40.8

6.4

LM135-LM235-LM335,A

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