SGP41-D-R4 datasheet(9/22 Pages) SENSIRION

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3 Sensor Output Signal Description

3.1 Conditioning

After each restart of the sensor or when the hotplates have been switched off, the sgp41_execute_conditioning command must

be called from idle mode before the master calls the first sgp41_measure_raw_signals command (Figure 7). The conditioning

heats the hotplate of the NOx pixel to a different temperature compared to the measurement mode enabling a faster switch-on

(as specified in Table 1) thereafter. It is recommended to execute the conditioning for 10 s, but 10 s must not be exceeded to

avoid damage to the sensing material. Thereafter, the VOC+NOx measurement mode can be entered by following the

instructions given in 3.2 Raw Signal Measurement. The conditioning command requires to send default input parameters (2

words + respective CRC bytes).

Figure 7 Standard process flow for executing the conditioning of SGP41.

Optionally, the master may already read out the raw signal of the VOC pixel (SRAW_VOC) during conditioning (Figure 8) since

the hotplate of the VOC pixel will already be set to the temperature used in the VOC+NOx measurement mode. After calling the

sgp41_execute_conditioning command and after a subsequent minimum waiting time of 50 ms, SRAW_VOC is returned as one

16-bit word followed by a CRC byte. The sgp41_execute_conditioning command can be called consecutively multiple times

during the conditioning period.

Figure 8 Optional process flow for executing the conditioning of SGP41 and reading out the VOC raw signal.

3.2 Raw Signal Measurement

Calling the sgp41_measure_raw_signals command launches/continues the VOC+NOx measurement mode. The first call of this

command should be performed after the conditioning (see 3.1 Conditioning). This command starts one measurement of the raw

signals of the VOC and the NOx pixel (SRAW_VOC, SRAW_NOX) which are returned after 50 ms. The two raw signal values in

ticks are provided as two 16-bit words each followed by one CRC byte (Figure 9). The raw signals in ticks are proportional each

to the logarithm of the corresponding sensor resistance. These tow signals are used as input for Sensirion’s Gas Index Algorithm

to provide processed VOC and NOx Indices (see section 3.3 VOC and NOx Index Measurement). In case the Gas Index Algorithm

is not used, discard the first measured value of each signal. Typically, a measurement is performed every second by calling the

sgp41_measure_raw_signals command again every second without turning the heater off. To exit the VOC+NOx measurement

mode, the master calls the sgp4x_turn_heater_off command which switches off the hotplates and puts the sensor in idle mode.

In order to avoid prolonged run-in of the NOx signal, it is recommended to keep the measurement running whenever possible.

SGP41-D-R4 数据表(PDF) 9 Page - Sensirion AG Switzerland