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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.

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

–

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).