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Analog Temperature Sensor – LM335

Rev 1.1

28/04/20

Thermocouple compensation

FIGURE 19. Thermocouple cold junction compensation (compensation for grounded thermocouple)

Thermocouple

R3

R4

SEEBECK

Coefficient

J

1.05kΩ

365Ω

52.3µV/°C

T

856Ω

315Ω

42.8µV/°C

K

816Ω

300Ω

40.8µV/°C

S

128Ω

46.3Ω

6.4µV/°C

Adjustments:

1. Adjust R1 for the voltage across R3 equal to the SEEBECK

coefficient times ambient temperature in degrees Kelvin.

2.

Adjust R2 for voltage across R4 corresponding to the

thermocouple as below:

J

14.32mV

K

11.17mV

T

11.9mV

S

1.768mV

FIGURE 20. Single power supply cold junction compensation

Thermocouple

R3

SEEBECK

Coefficient

J

377Ω

52.3µV/°C

T

308Ω

42.8µV/°C

K

293Ω

40.8µV/°C

S

45.8Ω

6.4µV/°C

Adjustments:

1. Short 1N4568.

2.

Adjust R1 for SEEBECK coefficient times ambient

temperature in degrees Kelvin across R3.

3. Short LM135 and adjust R2 for voltage across R3

corresponding to thermocouple type as below:

J

14.32mV

K

11.17mV

T

11.9mV

S

1.768mV

+15V

LM135

*Select R3 & R4 for proper

thermocouple type

+15V

LM135

*Select R3 for proper

thermocouple type