Derivative component update, add time_window (#11963)

* update the docs, see https://github.com/home-assistant/home-assistant/pull/31397

* add more detailed example
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Bas Nijholt 2020-02-04 10:31:38 +01:00 committed by GitHub
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@ -10,7 +10,8 @@ logo: derivative.png
ha_qa_scale: internal
---
The `derivative` platform provides the numerical derivative or numerical differentiation of the values provided by a source sensor. Derivative sensors are updated upon changes of the **source**. Fast sampling source sensors provide better results.
The `derivative` platform creates a sensor that estimates the derivative of the values provided by a source sensor.
Derivative sensors are updated upon changes of the **source**.
## Configuration
@ -39,7 +40,7 @@ round:
default: 3
type: integer
unit_prefix:
description: Metric unit to prefix the derivative result. Available units are k, M, G, T.
description: Metric unit to prefix the derivative result ([Wikipedia](https://en.wikipedia.org/wiki/Unit_prefix)]). Available symbols are "n" (1e-9), "µ" (1e-6), "m" (1e-3), "k" (1e3), "M" (1e6), "G" (1e9), "T" (1e12).
required: false
default: None
type: string
@ -52,6 +53,27 @@ unit:
description: Unit of Measurement to be used for the derivative.
required: false
type: string
time_window:
description: The time window in which to calculate the derivative. This is useful for sensor that output discrete values. By default the derivative is calculated between two consecutive updates.
default: 0
required: false
type: time
{% endconfiguration %}
If 'unit' is set then 'unit_prefix' and 'unit_time' are ignored.
## Temperature example
For example, you have a temperature sensor `sensor.temperature` that outputs a value every few seconds, but rounds to the nearest half number.
That means that two consecutive output values might be the same (so the derivative is `Δy/Δx=0` because `Δy=0` !)
However, the temperature might actually be changing over time.
In order to capture this, you should use a `time_window`, such that immediate jumps don't result in high derivatives and that after the next sensor update, the derivatives doesn't vanish to zero.
An example config that uses `time_window` is
```yaml
sensor:
- platform: derivative
source: sensor.temperature
name: Temperature change per hour
round: 1
unit_time: h
time_window: "00:30:00" # we look at the change over the last half hour
```