Combine the state of several sensors
====================================

.. seo::
    :description: Instructions for setting up a combination sensor

The ``combination`` sensor platform allows you to combine the state of several 
sensors into one. To use this sensor, specify the combination type and add your source sensors.

The ``unit_of_measurement``, ``device_class``, ``entity_category``, ``icon``, and
``accuracy_decimals`` properties are by default inherited from the first sensor.
``state_class`` is explicitly not inherited, because ``total_increasing`` states
could still decrease when multiple sensors are used for several of the combination types.

The source sensor states can be combined in several ways: 

- ``KALMAN`` filter: This type filters one or several
  sensors into one with a reduced error. If using a single sensor as data source,
  it acts like a :ref:`sensor-filter-exponential_moving_average` filter. With
  multiple sensors, it combines their values based on their respective standard
  deviation.

.. code-block:: yaml

    # Example configuration entry
    sensor:
      - platform: combination
        type: kalman
        name: "Temperature"
        process_std_dev: 0.001
        sources:
          - source: temperature_sensor_1
            error: 1.0
          - source: temperature_sensor_2
            error: !lambda |-
              return 0.5 + std::abs(x - 25) * 0.023

- ``LINEAR`` combination: This type sums all source sensors after multiplying each by 
  a configured coeffecient.

.. code-block:: yaml

    # Example configuration entry
    sensor:
      - platform: combination
        type: linear
        name: "Balance Power"
        sources:
          - source: total_power
            coeffecient: 1.0
          - source: circuit_1_power
            coeffecient: -1.0

- ``MAXIMUM``, ``MEAN``, ``MEDIAN``, ``MINIMUM``, ``MOST_RECENTLY_UPDATED``, 
  ``RANGE``, ``SUM`` combinations: These types compute the specified combination among
  all source sensor states.

.. code-block:: yaml

    # Example configuration entry
    sensor:
      - platform: combination
        type: median
        name: "Median Temperature"
        sources:
          - source: temperature_sensor_1
          - source: temperature_sensor_2
          - source: temperature_sensor_3

Configuration variables:
------------------------

- **type** (**Required**, enum): Combination statistic type, should be one of
  ``KALMAN``, ``LINEAR``, ``MAXIMUM``, ``MEAN``, ``MEDIAN``, ``MINIMUM``, 
  ``MOST_RECENTLY_UPDATED``, ``RANGE``, or ``SUM``.
- **sources** (**Required**, list): A list of sensors to use as source.
  
  - **source** (**Required**, :ref:`config-id` of a :doc:`/components/sensor/index`): The
    sensor id that is used as sample source.
  - **error** (**Required** - only for ``KALMAN`` type, float, :ref:`templatable <config-templatable>`): 
    The standard deviation of the sensor's measurements. This works like the ``process_std_dev`` 
    parameter, with low values marking accurate data. If implemented as a template, the 
    measurement is in parameter ``x``.
  - **coeffecient** (**Required** - only for ``LINEAR`` type, float, :ref:`templatable <config-templatable>`): 
    The coeffecient to multiply the sensor's state by before summing all source sensor states.
    If implemented as a template, the measurement is in parameter ``x``.

- **process_std_dev** (**Required** - only for ``KALMAN`` type, float): The standard deviation of the
  measurement's change per second (e.g. ``1/3600 = 0.000277`` if the
  temperature usually changes at most by one Kelvin per hour). A low value here
  will place high importance on the current state and be slow to respond to
  changes in the measured samples. A high value will update faster, but also be
  more noisy.
- **std_dev** (*Optional - only for KALMAN type*, :ref:`Sensor <config-sensor>`): A sensor
  that publishes the current standard deviation of the state with each update.
- All other options from :ref:`Sensor <config-sensor>`.

See Also
--------

- :ref:`sensor-filters`
- :apiref:`combination/combination.h`
- :ghedit:`Edit`