Datasheet
Final Datasheet
BME280 Environmental sensor
Page 15
BST-BME280-DS001-10 | Revision 1.1 | May 2015 Bosch Sensortec
© Bosch Sensortec GmbH reserves all rights even in the event of industrial property rights. We reserve all rights of disposal such as copying and passing on to
third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.
Note: Specifications within this document are subject to change without notice.
3.4.1 Humidity measurement
The humidity measurement can be enabled or skipped. When enabled, several oversampling
options exist. The humidity measurement is controlled by the osrs_h[2:0] setting, which is
detailed in chapter 5.4.3. For the humidity measurement, oversampling is possible to reduce the
noise. The resolution of the humidity measurement is fixed at 16 bit ADC output.
3.4.2 Pressure measurement
Pressure measurement can be enabled or skipped. When enabled, several oversampling
options exist. The pressure measurement is controlled by the osrs_p[2:0] setting which is
detailed in chapter 5.4.5. For the pressure measurement, oversampling is possible to reduce
the noise. The resolution of the pressure data depends on the IIR filter (see chapter 3.4.4) and
the oversampling setting (see chapter 5.4.5):
When the IIR filter is enabled, the pressure resolution is 20 bit.
When the IIR filter is disabled, the pressure resolution is 16 + (osrs_p 1) bit, e.g. 18 bit
when osrs_p is set to 3
3.4.3 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. The temperature measurement is controlled by the osrs_t[2:0] setting which is detailed in
chapter 5.4.5. For the temperature measurement, oversampling is possible to reduce the noise.
The resolution of the temperature data depends on the IIR filter (see chapter 3.4.4) and the
oversampling setting (see chapter 5.4.5):
When the IIR filter is enabled, the temperature resolution is 20 bit.
When the IIR filter is disabled, the temperature resolution is 16 + (osrs_t 1) bit, e.g. 18
bit when osrs_t
3.4.4 IIR filter
The humidity value inside the sensor does not fluctuate rapidly and does not require low pass
filtering. However, 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 BME280 features an internal IIR filter. It effectively reduces the bandwidth of the
temperature and pressure output signals
10
and increases the resolution of the pressure and
temperature output data to 20 bit. The output of a next measurement step is filtered using the
following formula:
Data_filtered_old is the data coming from the current filter memory, and data_ADC is the data
coming from current ADC acquisition. Data_filtered is the new value of filter memory and the
value that will be sent to the output registers.
The IIR filter can be configured to different filter coefficients, which slows down the response to
the sensor inputs. Note that the response time with enabled IIR filter depends on the number of
10
Since the BME280 does 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.