LM135, LM135A, LM235, LM235A, LM335, LM335A

www.ti.com

SNIS160E – MAY 1999 – REVISED FEBRUARY 2015

System Examples (continued)

8.3.1 Thermocouple Cold Junction Compensation

Compensation for Grounded Thermocouple

Select R3 for proper thermocouple type

Figure 24. Thermocouple Cold Junction Compensation

THERMO-COUPLE

R3 (±1%)

SEEBECK COEFFICIENT

J

377

Ω

52.3

μV/°C

T

308

Ω

42.8

μV/°C

K

293

Ω

40.8

μV/°C

S

45.8

Ω

6.4

μV/°C

Adjustments: Compensates for both sensor and resistor tolerances

1.

Short LM329B

2.

Adjust R1 for Seebeck Coefficient times ambient temperature (in degrees K) across R3.

3.

Short LM335 and adjust R2 for voltage across R3 corresponding to thermocouple type.

J

14.32 mV

K

11.17 mV

T

11.79 mV

S

1.768 mV

THERMO-COUPLE

R3

R4

SEEBECK COEFFICIENT

J

1.05K

385

Ω

52.3

μV/°C

T

856

Ω

315

Ω

42.8

μV/°C

K

816

Ω

300

Ω

40.8

μV/°C

S

128

Ω

46.3

Ω

6.4

μV/°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 thermocouple.

J

14.32 mV

T

11.79 mV

K

11.17 mV

S

1.768 mV

Copyright © 1999–2015, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LM135 LM135A LM235 LM235A LM335 LM335A