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SHT1X

Humidity & Temperature Sensor

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SHT1x / SHT7x Relative Humidity & Temperature Sensor System

3 Converting Output to Physical Values

3.1 Relative Humidity

To compensate for the non-linearity of the humidity sensor

and to obtain the full accuracy it is recommended to convert

the readout with the following formula1:

RHlinear = c1 + c 2 • SORH + c 3 • SORH2

SORH

c1

c2

c3

12 bit

-4

0.0405 -2.8 * 10-6

8 bit

-4

0.648 -7.2 * 10-4

Table 6 Humidity conversion coefficients

For simplified, less computation intense conversion formulas

see application note “RH and Temperature Non-Linearity

Compensation”.

The humidity sensor has no significant voltage dependency.



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SORH sensor readout (12bit)

Figure 10 Conversion from SORH to relative humidity

3.1.1 Humidity Sensor RH/Temperature compensation

For temperatures significantly different from 25 °C (~77 °F)

the temperature coefficient of the RH sensor should be

considered:

RHtrue = (T°C - 25)•(t1 + t 2 •SORH) +RHlinear

SORH

t1

t2

12 bit

0.01

0.00008

8 bit

0.01

0.00128

Table 7 Temperature compensation coefficients

This equals ~0.12 %RH / °C @ 50 %RH

3.2 Temperature

The bandgap PTAT (Proportional To Absolute Temperature)

temperature sensor is very linear by design. Use the

following formula to convert from digital readout to

temperature:

Temperature = d1 + d2 •SOT

VDD d1 [°C]

5V -40.00

4V -39.75

3.5V -39.66

3V -39.60

2.5V -39.55

d1 [°F]

-40.00

-39.50

-39.35

-39.28

-39.23

SOT

14bit

12bit

d2 [°C] d2 [°F]

0.01 0.018

0.04 0.072

Table 8 Temperature conversion coefficients

For improved accuracies in extreme temperatures with more

computation intense conversion formulas see application

note “RH and Temperature Non-Linearity Compensation”.

3.3 Dewpoint

Since humidity and temperature are both measured on the

same monolithic chip, the SHTxx allows superb dewpoint

measurements. See application note “Dewpoint calculation”

for more.

1 Where SORH is the sensor output for relative humidity

www.sensirion.com

v2.02 July 2004

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