SHT1x / SHT7x Relative Humidity & Temperature Sensor System

www.sensirion.com

v2.02 July 2004

5/9

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

2

RH

3

RH

2

1

linear

SO

c

SO

c

c

RH

•

+

•

+

=

12 bit

-4

0.0405

8 bit

-4

0.648

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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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:

linear

RH

2

1

C

true

RH

)

SO

t

(t

25)

-

(T

RH

+

•

+

•

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:

T

2

1

SO

d

d

e

Temperatur

•

+

=

VDD

5V

-40.00

-40.00

14bit

0.01

0.018

4V

-39.75

-39.50

12bit

0.04

0.072

3.5V

-39.66

-39.35

3V

-39.60

-39.28

2.5V

-39.55

-39.23

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.