Datasheet

www.sensirion.com
Version 1.0 – July 2020 – D1
13/19
Measure Raw Signal
Command
Subcommand
Command hex. code
Description
sgp40_measure_raw
Without humidity
compensation
0x26 0F 80 00 A2 66 66 93
This command starts/continues the VOC
measurement mode, leaves humidity compensation
disabled by sending the default values (see Table 10),
and returns the measured raw signal SRAW as 2 bytes
(+ 1 CRC byte).
With humidity
compensation
0x26 0F XX XX XX YY YY YY
This command starts/continues the VOC
measurement mode, enables humidity compensation,
and returns the measured raw signal SRAW as 2 bytes
(+ 1 CRC byte). The humidity compensation feature
requires a relative humidity XX XX XX and
temperature YY YY YY input (incl. corresponding CRC
bytes) in the format as given in Table 10.
Table 9 Description of the I
2
C measurement command.
Relative Humidity
Temperature
Value / %
Hex. code
Value / °C
Hex. code
Conversion into ticks
RH/ticks=RH/%×
65'535
100
T/ticks=
(
T/°C + 45
)
×
65'535
175
Default
50
0x80 00 + CRC 0xA2
25
0x66 66 + CRC 0x93
Minimum
0
0x00 00 + CRC 0x81
−45
0x00 00 + CRC 0x81
Maximum
100
0xFF FF + CRC 0xAC
130
0xFF FF + CRC 0xAC
Table 10 Conversion of relative humidity in % and temperature in °C into ticks as the input parameters of the measurement command. Note:
minimum and maximum values do not reflect the range of conditions for which the humidity compensation feature has been optimized. For
details see Table 4.
Byte number
Description
Value
0, 1
two bytes
u16 unsigned integer directly provides the raw signal SRAW in
ticks which is proportional to the logarithm of the resistance of the
sensing element.
2
CRC byte for bytes 0, 1
–
Table 11 Returned values by the I
2
C measurement command.
Built-in Self-Test
Command
Command hex. code
Description
sgp40_measure_test
0x28 0E
This command triggers the built-in self-test checking for integrity
of both hotplate and MOX material and returns the result of this
test as 2 bytes (+ 1 CRC byte).
Table 12 Description of the I
2
C built-in self-test command.