www.sensirion.com / D1

Version 2

– July 2021

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4.6 Serial number

Each 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 command 0x89 and is transmitted as two 16-bit words, each

followed by an 8-bit CRC.

4.7 Reset & Abort

A reset of the sensor can be achieved in three ways:

• Soft reset: send the reset command described in Table 7.

• I2C general call reset: all devices on I2C bus are reset by sending the command 0x06 to

the I2C address 0x00.

• Power down (incl. pulling SCL and SDA low)

Any command that triggers an action at the sensor can be aborted via I2C general call reset or soft

reset.

4.8 Heater Operation

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

commands given in Table 7. Three heating powers and two heating durations are selectable. 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

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

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 5%. To obtain a fast

increase in temperature the idle time between consecutive heating pulses shall be kept minimal.

Possible Heater Use Cases

There will be dedicated Sensirion application notes elaborating on various use cases of the

heater. In general, the applications of the on-chip heater range around:

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. Creep-free operation in high humid environments. Periodic heating pulses allow for creep-

free high-humidity measurements for extended times.

Important notes for operating the heater:

1. The heater is designed for a maximum duty cycle of 5%, meaning the total heater-on-time

should not be longer than 5% of the sensor

’s lifetime.

2. During operation of the heater, sensor specifications are not valid.

3. The temperature sensor can additionally be affected by the thermally induced mechanical

stress, offsetting the temperature reading from the actual temperature.

4.

The sensor’s temperature (base temperature + temperature increase from heater) must

not exceed Tmax = 125 °C in order to have proper electrical functionality of the chip.

5. The heater draws a large amount of current once enabled (up to ~75mA in the highest

power setting). Although a dedicated circuitry draws this current smoothly, the power