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N.B.: The RH conversion formula (1) allows values to be reported which are outside of the range of

0 %RH … 100 %RH. Relative humidity values which are smaller than 0 %RH and larger than 100 %RH are non-

physical, however these “uncropped” values might be found beneficial in some cases (e.g. when the distribution

of the sensors at the measurement boundaries are of interest). For all users who don’t want to engage in

evaluation of these non-physical values, cropping of the RH signal to the range of 0 %RH … 100 %RH is advised.

N.B. 2: From a computational perspective, in formulae (1), ( 2 ), and ( 3 ) the division by 2^16-1 can be simplified

to a division by only 2^16. The introduced accuracy deviations are <0.002 %RH and <0.003 °C, respectively.

5.6 Serial Number

Every single sensor has a unique serial number, that is assigned by Sensirion during production. It is stored in

the one-time-programmable memory and cannot be manipulated after production. The serial number is

accessible via I2C and is transmitted as two 16-bit words, each followed by an 8-bit CRC.

5.7 I2C Heater Operation

The sensor incorporates an integrated on-chip heater which can be switched on by the set of commands given

Table 7. There are three different heating powers and two different heating times accessible to the user whixh

are given in . After reception of a heater-on command, the sensor executes the following procedure:

1. The heater is enabled, and the timer starts its count-down.F

2. On timer expiration a temperature and humidity measurement with the highest repeatability is started,

the heater remains enabled.

3. After the measurement is finished the heater is turned off.

4. Temperature and humidity values are now available for readout.

The maximum on-time of the heater commands is 1 second in order to prevent overheating of the sensor by

unintended usage of the heater. Thus, there is no dedicated command to turn off the heater. For extended

heating periods it is required to send periodic heater-on commands, keeping in mind that the heater is

designed for a maximal duty cycle of less than 10%. To obtain a fast increase in temperature the idle time

between consecutive heating pulses shall be kept minimal.

Parameter

Selectable Values

Heater Power (for VDD = 5V

0 (=off), 20, 110, 200 mW

Heater-on Duration (tHeat)

0.1, 1 s

Maximal duty cycle

10%

Table 10. SHT41A-AWSB heater specifications.

5.8 Possible Heater Use Cases

Please refer to the dedicated Sensirion application notes elaborating on various use cases of the heater. In

general, the applications of the on-chip heater cover:

1. Removal of condensed / spray water on the sensor surface. Although condensed water is not a

reliability / quality problem to the sensor, it will however make the sensor non-responsive to RH

changes in the air as long as there is liquid water on the surface.

2. Drift-free operation in high humid environments. Periodic heating pulses allow for drift-free high-

humidity measurements over extended periods of times.