Rain Sensor Heater Algorithm

Algorithm for the heater of the rain sensor

The rain sensor heating adjustments are regulated by the constants defined under the
Device section of the Setup TAB as illustrated below by the red, blue and green
rectangles.

The red rectangle parameters

The red rectangle parameters define the target temperature for the rain sensor in terms of
the ambient temperature.

• The field TEMP of the LOW column corresponds to the ambient temperature
  (ºC), below which the rain sensor operational temperature is kept at the value
  defined in the DELTA field. For example, in the case illustrated in figure above,
  for ambient temperatures below 0ºC the rain sensor operational temperature will
  be kept at 6ºC.
• The field TEMP of the HIGH column corresponds to the ambient temperature
  (ºC), above which the rain sensor operational temperature will be kept at the
  ambient temperature + the value defined in the DELTA field. For example, in the
  case illustrated in figure above, for temperatures greater than 20ºC the rain sensor
  operational temperature will be adjusted to the ambient temperature + 4ºC.
• For ambient temperatures comprised between LOW TEMP and HIGH TEMP
  values, the system will calculate an increment which is directly proportional to the

ambient temperature and limited by the LOW DELTA and HIGH DELTA values.

This increment is added to the ambient temperature to establish the rain sensor
target temperature.

The green rectangle parameters

The parameter Min enclosed by the green rectangle corresponds to the minimum heating
value. This value corresponds to a percentage and it should be between 10 and 20 for
stable behavior.

The blue rectangle parameters

The system will generate a heating impulse based on the parameters enclosed in the blue
rectangle.

• This parameter may create a situation where the rain sensor temperature is above
  the value calculated by the previous parameters. Under these circumstances the
  system will respect the minimum heating value even if the temperature is above
  the target temperature calculated using with the red rectangle parameters.

• The Heat Impulse mechanism has the objective to dry the rain sensor surface if
  the rain sensor stays continuously WET/RAIN for the period of time defined by
  the CYCLE field (in seconds).
• The duration of the pulse is given by the DURAT field (in seconds) and the pulse
  intensity is calculated in terms of the rain sensor temperature as the value of the
  ambient temperature (ºC) + the TEMP field (ºC). In the case illustrated in the
  above figure, the heat impulse will have the duration of 60 seconds at a
  temperature 10ºC higher than the ambient temperature if the rain sensor stays
  WET/RAIN for a continuous period of at least 600 seconds (i.e. 10 minutes).

> 8 ºC

40%

> 4º C

20%

> 3 º C

10%

> 2 º C

6%

> 1º C

4%

> 0.5 º C

2%

> 0.3 º C

1%

Internal algorithm

For every read cycle, the target temperature for the rain sensor is calculated based on the
actual ambient temperature and the red rectangle parameters described above.

The power adjustments performed to the rain heater power depend on the read
cycle period and the difference between the actual temperature and the target
temperature.

For the default read cycle of 10 seconds, the following table is used to
determine the variation to the rain sensor heating power

Temperature difference

between

Actual Temperature

and

Target Temperature

Percentage
variation to the
rain sensor
heating power

When the heat impulse mechanism is initiated, the power to the rain sensor is
increased to 100% and it is kept at 100% while the rain sensor has not reached
the impulse temperature (= the ambient temperature + Temp. parameter in the
blue rectangle).

The moment the rain sensor reaches this impulse temperature, the system will
consider this impulse temperature the target temperature and it will manage
the rain sensor temperature using the same approach as defined in 1 and 2

1. If the actual rain sensor temperature is above the calculated target temperature,
   then the rain sensor heater power is decreased. However, if the new rain heater
   power falls below the Minimum value (defined by the green rectangle parameter)
   then this Minimum value is used.
2. If the actual rain sensor temperature is below the calculated target temperature,
   then the rain sensor heater power is increased.

3. If the rain sensor value has been wet/rain for at least the Cycle value (defined in
   the blue rectangle) the system will activate the heat impulse mechanism.

above, keeping the rain sensor at this target temperature (= Impulse
temperature) for the period defined in the blue rectangle parameters Durat.

After the period defined by Durat the system will revert to its normal
operation, calculating the target temperature based on the red rectangle
parameters and the ambient temperature.