Datasheet SHT1x

www.sensirion.com

Version 5 – December 2011

8/12

Bit Type Description

Default

7

reserved

0

6 R

End of Battery (low voltage

detection)

‘0’ for VDD > 2.47

‘1’ for VDD < 2.47

X

No default value,

bit is only updated

after a

measurement

5

reserved

0

4

reserved

0

3

For Testing only, do not use

0

2 R/W

Heater

0 off

1 R/W

no reload from OTP

0 reload

0 R/W

’1’ = 8bit RH / 12bit Temp.

resolution

’0’ = 12bit RH / 14bit Temp.

resolution

0

12bit RH

14bit Temp.

Table 5: Status Register Bits

Measurement resolution: The default measurement

resolution of 14bit (temperature) and 12bit (humidity) can

be reduced to 12 and 8bit. This is especially useful in high

speed or extreme low power applications.

End of Battery function detects and notifies VDD voltages

below 2.47V. Accuracy is

±0.05V.

Heater: An on chip heating element can be addressed by

writing a command into status register. The heater may

beyond ambient temperature. The heater draws roughly

8mA @ 5V supply voltage.

For example the heater can be helpful for functionality

analysis: Humidity and temperature readings before and

after applying the heater are compared. Temperature shall

increase while relative humidity decreases at the same

time. Dew point shall remain the same.

Please note: The temperature reading will display the

temperature of the heated sensor element and not

ambient temperature. Furthermore, the sensor is not

qualified for continuous application of the heater.

OTP reload: With this operation the calibration data is

uploaded to the register before each measurement. This

may be deactivated for reducing measurement time by

about 10ms.

4 Conversion of Signal Output

4.1

Relative Humidity

For compensating non-linearity of the humidity sensor –

see Figure 18 – and for obtaining the full accuracy of the

sensor it is recommended to convert the humidity readout

Table 6:

2

RH

3

RH

2

1

linear

SO

c

SO

c

c

RH

⋅

+

⋅

+

=

(%RH)

12 bit

-2.0468

0.0367

-1.5955E-6

8 bit

-2.0468

0.5872

-4.0845E-4

Table 6: Humidity conversion coefficients

Values higher than 99% RH indicate fully saturated air and

note that the humidity sensor has no significant voltage

dependency.

0%

20%

40%

60%

80%

100%

0

500

1000

1500

2000

2500

3000

3500

4.2

Temperature compensation of Humidity Signal

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

the humidity signal requires temperature compensation.

The temperature correction corresponds roughly to

0.12%RH/°C @ 50%RH. Coefficients for the temperature

compensation are given in Table 7.

(

) (

)

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

4.3

Temperature

The

band-gap

PTAT

(Proportional

To

Absolute

Temperature) temperature sensor is very linear by design.

to temperature value, with coefficients given in Table 8:

T

2

1

SO

d

d

T

⋅

+

=

sensor output signal can drop below 100%RH (even below 0%RH in some

cases), but the sensor will recover completely when water droplets

evaporate. The sensor is not damaged by water immersion or condensation.