129 lines
3.9 KiB
ReStructuredText
129 lines
3.9 KiB
ReStructuredText
NTC Sensor
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==========
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.. seo::
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:description: Instructions for setting up NTC thermistor sensor in ESPHome
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:image: ntc.jpg
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The ``ntc`` platform is a helper sensor that allows you to convert resistance readings
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from a NTC thermistor to temperature readings.
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First, you need to get resistance readings from the sensor - you can set this up with the
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:doc:`resistance <resistance>` and :doc:`adc <adc>` sensors.
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This platform will then convert the resistance values to temperature readings.
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It also requires calibration parameters for this conversion. There are two
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ways of obtaining these values: By looking at the datasheet or manual calculation.
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If you have the datasheet of the thermistor, you can look at its "B-constant" and
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reference temperature/resistance. For example `this product <https://www.adafruit.com/product/372>`__
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would have the following calibration configuration.
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.. code-block:: yaml
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# Example configuration entry
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sensor:
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- platform: ntc
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# ...
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calibration:
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b_constant: 3950
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reference_temperature: 25°C
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reference_resistance: 10kOhm
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If you don't have access to the datasheet or want to calculate these values yourself,
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you have to first measure three resistance values at different temperatures.
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Heat/cool the NTC to three different temperatures (best if temperatures are far apart)
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and write down the resistance readings at those temperatures. Then enter these values in the
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calibration parameter:
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.. code-block:: yaml
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# Example configuration entry
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sensor:
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- platform: ntc
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# ...
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calibration:
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- 10.0kOhm -> 25°C
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- 27.219kOhm -> 0°C
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- 14.674kOhm -> 15°C
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.. code-block:: yaml
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# Example configuration entry
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sensor:
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- platform: ntc
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sensor: resistance_sensor
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calibration:
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b_constant: 3950
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reference_temperature: 25°C
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reference_resistance: 10kOhm
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name: NTC Temperature
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# Example source sensors:
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- platform: resistance
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id: resistance_sensor
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sensor: source_sensor
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configuration: DOWNSTREAM
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resistor: 5.6kOhm
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name: Resistance Sensor
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- platform: adc
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id: source_sensor
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pin: A0
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Configuration variables:
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------------------------
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- **name** (**Required**, string): The name for the sensor.
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- **sensor** (**Required**, :ref:`config-id`): The sensor to read the resistance values from
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to convert to temperature readings.
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- **calibration** (**Required**, float): The calibration parameters of the sensor - see above
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for more details.
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- **id** (*Optional*, :ref:`config-id`): Set the ID of this sensor for use in lambdas.
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- All other options from :ref:`Sensor <config-sensor>`.
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Self-Heating
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------------
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A constant voltage supply to the NTC sensor causes it to heat up and therefore creates unreliable temperature values.
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So it's recommended to only supply the NTC sensor (and voltage divider) during the actual measurement.
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More info `here <https://learn.adafruit.com/thermistor/using-a-thermistor#self-heating-3-22>`__.
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To do this, replace the 3.3V side of the voltage divider with a connection to a GPIO pin. This GPIO pin will
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be switched HIGH (3.3V) only during the measurement, thus preventing the sensor from heating up.
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In the example below, the pin ``D0`` is the "top" side of the voltage divider:
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.. code-block:: yaml
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sensor:
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# Same as before:
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- platform: ntc
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sensor: resistance_sensor
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# ...
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- platform: adc
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pin: A0
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id: source_sensor
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# Added:
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update_interval: never
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switch:
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- platform: gpio
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pin: D0
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id: ntc_vcc
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interval:
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- interval: 60s
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then:
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- switch.turn_on: ntc_vcc
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- component.update: source_sensor
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- switch.turn_off: ntc_vcc
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See Also
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--------
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- :doc:`adc`
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- :doc:`resistance`
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- :ref:`sensor-filters`
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- :apiref:`ntc/ntc.h`
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- :ghedit:`Edit`
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