DALI · Interface guide
Calculated parameters
Every built-in equation offered for a Calculated parameter, grouped as in the Equation Type list, with the inputs each one needs and what it gives you.
A calculated parameter is worked out by the station from other parameters, or from the station's position and clock. You create one on the Parameters page: set Type to Calculated, then pick an Equation Type. The form then shows one picker per input.
Who can use them: Admin and Factory.
How inputs work:
- An input marked parameter is picked from the station's existing parameters. Create those first.
- An input marked number is a constant you type in, such as a coefficient from a data sheet.
- Every parameter input must be filled in before the station will save.
- A calculated parameter can be the input of another one. For example, Soiling Rate takes a Soiling Ratio parameter.
- Scaling and Offset on the calculated parameter still apply to the result, except for the sunrise, sunset and solar noon times, where they are switched off.
- Several equations report 999 when they cannot give a valid value, for example when an input is missing or out of range, or when there is not enough light for a soiling measurement.
Weather / Environmental
| Equation | Inputs | What it gives |
|---|---|---|
| Dew Point | Air Temperature (parameter), Humidity (parameter) | Dew point temperature, by the Magnus formula. |
| Water Vapour Pressure (from Dew Point) | Dew Point Temperature in °C (parameter) | Water vapour pressure at that dew point. |
| Water Vapour Pressure (from Relative Humidity) | Air Temperature in °C (parameter), Relative Humidity in % (parameter) | Actual water vapour pressure of the air. |
| Air Density | Air Pressure in hPa, Air Temperature in °C, Relative Humidity in %, Partial Water Vapour Pressure in hPa (all parameters) | Density of moist air. For the fourth input use a Water Vapour Pressure parameter. Below 20 % humidity the station uses the dry-air formula. |
| 3-Second Wind Gust | Wind Speed (parameter) | The running 3-second mean of wind speed. |
| 1-Minute Wind Gust | Wind Speed (parameter) | The highest 3-second mean in each minute, reported at the end of the minute. Use the raw wind speed as input. |
| 10-Minute Wind Gust | Wind Speed (parameter) | The same over each 10-minute period, reported at :00, :10, :20 and so on. |
| 3-Second Wind Direction | Wind Direction, 3-Sec Wind Gust (parameters) | The current wind direction while there is wind, and 0 in calm. |
| 1-Minute Wind Direction | Wind Direction, 3-Sec Wind Gust (parameters) | The wind direction at the moment of the strongest gust in each minute. |
| 10-Minute Wind Direction | Wind Direction, 3-Sec Wind Gust (parameters) | The same for each 10-minute period. |
Solar / Energy
| Equation | Inputs | What it gives |
|---|---|---|
| Total Solar Radiation | Solar Irradiance in W/m² (parameter) | The day's total solar energy in kWh/m². The irradiance is added once a minute, and the total starts again each day. |
| Albedo | Incoming Radiation, Reflected Radiation (parameters) | Reflected divided by incoming radiation. |
| DNI Calculation | Global Horizontal Irradiance (GHI), Diffuse Horizontal Irradiance (DHI) (parameters) | Direct normal irradiance, (GHI minus DHI) divided by the cosine of the sun's zenith angle. The station works out the sun's position itself. It gives 0 when the sun is at or below the horizon. |
| Sunrise Time | None | Today's local sunrise, shown as HH:MM. |
| Sunset Time | None | Today's local sunset, shown as HH:MM. |
| Local Solar Noon | None | Today's local solar noon, shown as HH:MM. |
| Zenith Angle | None | The sun's angle from straight overhead, in degrees (0 overhead, 90 at the horizon). |
| Target Temperature (Apogee SI-121-SS) | Sensor Body Temperature in K, m Coefficient, b Coefficient, Target Sensor Reading in mV (parameters) | The target temperature in kelvin for an Apogee SI-121-SS sensor, from its body temperature and signal. |
The four sun equations use the station's location. The form shows the coordinates in use and where they come from (manual entry, live GPS, or last good GPS fix). Set them on Device, General under Location Coordinates.
The sun times are stored as a number such as 6.30 for 06:30, so that they fit in one Modbus value. The console shows them as a time of day.
Soiling / PV
These equations measure how much dust on solar panels reduces their output, by comparing a soiled reference panel with a clean one. They build on each other, so create them in this order.
| Equation | Inputs | What it gives |
|---|---|---|
| Soiled Panel Irradiance (W/m²) | Soiled Panel ISC in A, Soiled Panel Temperature in °C (parameters); Alpha in °C⁻¹, Temperature STC in °C (default 25), ISC at STC in A (numbers) | The irradiance the soiled panel sees, from its short-circuit current, corrected for temperature. |
| Clean Panel Irradiance (W/m²) | Clean Panel ISC in A, Clean Panel Temperature in °C (parameters); Alpha, Temperature STC (default 25), ISC at STC (numbers) | The same for the clean panel. |
| Expected Short Circuit Current (A) | Clean Panel Irradiance in W/m², Soiled Panel Temperature in °C (parameters); Alpha, Temperature STC (default 25), ISC at STC (numbers) | The current the soiled panel would give if it were clean. |
| Soiling Ratio (Raw) | Soiled Panel Current, Expected Short Circuit Current, Clean Panel Current, Clean Panel Irradiance (parameters); Irradiance Threshold in W/m² (number, 0 means 750) | Soiled current divided by expected current, only while clean-panel irradiance is above the threshold. Sudden drops, and values above 1.05, are held back as likely errors. |
| Soiling Ratio (Fixed System) | Local Solar Noon (parameter), Raw Soiling Ratio (parameter) | The day's soiling ratio for a fixed-tilt system, from samples within an hour either side of solar noon, confirmed after sunset. |
| Soiling Ratio (Tilted System) | Tilt Angle in ° (parameter), Raw Soiling Ratio (parameter) | The day's soiling ratio for a tracking system, from samples taken while the tilt is within 35° of flat, confirmed after sunset. |
| DustIQ Soiling Ratio | Soiling Ratio (1), Soiling Ratio (2) (parameters) | The average of the two soiling ratios of a DustIQ sensor. |
| Soiling Rate | Soiling Ratio (parameter) | The change in the confirmed soiling ratio from one day to the next. |
| Soiling Level | Soiling Ratio (parameter) | 1 minus the soiling ratio. |
| Soiling Index | Soiling Ratio (parameter) | The soiling level as a percentage: 100 minus the ratio x 100. |
Soiling ratios can be normalised against a freshly cleaned reference panel. Ask Aeron support if your station needs this.
Cumulative / Utility
| Equation | Inputs | What it gives |
|---|---|---|
| Rain Daily Cumulative | Rain Gauge (parameter) | The day's rainfall, adding each minute's rain. It starts again at midnight. Set the rain gauge parameter's Sampling to Cumulative. |
| Addition (Sum of Params) | Parameter 1, Parameter 2 (parameters). + Add Another Parameter adds more, up to 20 in all. | The sum of the inputs. |
| Average of Parameters | Parameter 1, Parameter 2, and more, up to 20 in all | The average of the inputs. |
| 2nd Order (a·x² + b·x + c) | x (parameter); a, b, c (numbers) | A polynomial of one parameter, for example a sensor correction curve. |
| 3rd Order (a·x³ + b·x² + c·x + d) | x (parameter); a, b, c, d (numbers) | The same with a cubic term. |
Statistics
| Equation | Inputs | What it gives |
|---|---|---|
| Standard Deviation (sliding window) | Source Parameter (parameter); Window in seconds (number, default 60) | The standard deviation of the parameter over the last window of readings. |
Common problems
| What you see | What it means | What to do |
|---|---|---|
| The input pickers are empty | There are no parameters to choose from yet. | Create the input parameters first. |
| "This calculation type requires at least 2 input parameter(s)." | An input is missing. | Fill in every input. |
| The value stays at 999 | The equation cannot give a valid value right now. | Check the inputs have values. Soiling values need enough sunlight. Sun equations need a location. |
| Sun times look wrong by whole hours | The station's time zone or location is wrong. | Check Device, Time and Location Coordinates. |
| Maximum 20 input parameters | Addition and Average take up to 20 inputs. | Split into two calculated parameters and add those. |