bmp280 datasheet

Bosch
Sensortec | BMP280 Data sheet
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Modifications reserved | Data subject to change without notice
Document number: BST-BMP280-DS001-23 Revision_1.23_11202
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3.3.2 Temperature measurement
Temperature measurement can be enabled or skipped. Skipping the measurement could be useful to
measure pressure extremely rapidly. When enabled, several oversampling options exist. Each
oversampling step reduces noise and increases the output resolution by one bit, which is stored in the
XLSB data register 0xFC. Enabling/disabling the temperature measurement and oversampling setting
are selected through the osrs_t[2:0] bits in control register 0xF4.
Table 5: osrs_t settings
osrs_t[2:0] Temperature oversampling Typical temperature
resolution
000 Skipped
(output set to 0x80000)
–
001 ×1 16 bit / 0.0050 °C
010 ×2 17 bit / 0.0025 °C
011 ×4 18 bit / 0.0012 °C
100 ×8 19 bit / 0.0006 °C
101, 110, 111 ×16 20 bit / 0.0003 °C
It is recommended to base the value of osrs_t on the selected value of osrs_p as per Table 4.
Temperature oversampling above ×2 is possible, but will not significantly improve the accuracy of the
pressure output any further. The reason for this is that the noise of the compensated pressure value
depends more on the raw pressure than on the raw temperature noise. Following the recommended
setting will result in an optimal noise-to-power ratio.
3.3.3 IIR filter
The environmental pressure is subject to many short-term changes, caused e.g. by slamming of a
door or window, or wind blowing into the sensor. To suppress these disturbances in the output data
without causing additional interface traffic and processor work load, the BMP280 features an internal
IIR filter. It effectively reduces the bandwidth of the output signals
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. The output of a next measurement
step is filter using the following formula:
tcoefficienfilter
ADCdatatcoefficienfilteroldfiltereddata
filtered
data
_
_)1_(__
_
+−⋅
=
where data_filtered_old is the data coming from the previous acquisition, and data_ADC is the data
coming from the ADC before IIR filtering.
The IIR filter can be configured using the filter[2:0] bits in control register 0xF5 with the following
options:
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Since most pressure sensors do not sample continuously, filtering can suffer from signals with a frequency higher than the
sampling rate of the sensor. E.g. environmental fluctuations caused by windows being opened and closed might have a frequency
<5 Hz. Consequently, a sampling rate of ODR = 10 Hz is sufficient to obey the Nyquist theorem.