LM135, LM135A, LM235, LM235A, LM335, LM335A

SNIS160D – MAY 1999 – REVISED MARCH 2013

www.ti.com

APPLICATION INFORMATION

CALIBRATING THE LM135

Included on the LM135 chip is an easy method of calibrating the device for higher accuracies. A pot connected

across the LM135 with the arm tied to the adjustment terminal allows a 1-point calibration of the sensor that

corrects for inaccuracy over the full temperature range.

This single point calibration works because the output of the LM135 is proportional to absolute temperature with

the extrapolated output of sensor going to 0V output at 0°K (

−273.15°C). Errors in output voltage versus

temperature are only slope (or scale factor) errors so a slope calibration at one temperature corrects at all

temperatures.

The output of the device (calibrated or uncalibrated) can be expressed as:

(1)

calibrating the output to read correctly at one temperature the output at all temperatures is correct. Nominally the

output is calibrated at 10 mV/°K.

To insure good sensing accuracy several precautions must be taken. Like any temperature sensing device, self

heating can reduce accuracy. The LM135 should be operated at the lowest current suitable for the application.

Sufficient current, of course, must be available to drive both the sensor and the calibration pot at the maximum

operating temperature as well as any external loads.

If the sensor is used in an ambient where the thermal resistance is constant, self heating errors can be calibrated

out. This is possible if the device is run with a temperature stable current. Heating will then be proportional to

zener voltage and therefore temperature. This makes the self heating error proportional to absolute temperature

the same as scale factor errors.

WATERPROOFING SENSORS

Meltable inner core heat shrinkable tubing such as manufactured by Raychem can be used to make low-cost

waterproof sensors. The LM335 is inserted into the tubing about ½

″ from the end and the tubing heated above

the melting point of the core. The unfilled ½

″ end melts and provides a seal over the device.

Typical Applications

Figure 15. Basic Temperature Sensor

Figure 17. Wide Operating Supply

Figure 16. Calibrated Sensor

*Calibrate for 2.982V at 25°C

6

Submit Documentation Feedback

Copyright © 1999–2013, Texas Instruments Incorporated

Product Folder Links: LM135 LM135A LM235 LM235A LM335 LM335A