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Document number: BST-BMP280-DS001-26 Revision_1.26_102021

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 signals6. The output of a next measurement

step is filter using the following formula:

coefficien

filter

ADC

data

coefficien

filter

old

filtered

data

filtered

data

)

(

−

⋅

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:

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.

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