Regarding "bind a custom property to engUnit on the tag" above, the goal would be to allow conversion from any unit to another of the operator's choosing. The conversion would be a two-step process, but straightforward. Ex: "R" --> "degF" --> "degC" (where 'degF' is selected as your 'standard' for temperature conversion). Consider building a table (as a tag and/or session prop?) which contains everything needed for any unit conversion to another. Something resembling:
| Units | Type | Factor | Offset |
|---|---|---|---|
| psig | Pressure | 1 | 0 |
| psia | Pressure | 1 | -14.6959 |
| inHg | Pressure | 0.491154 | 0 |
| inH2O | Pressure | 0.0360912 | 0 |
| kPa | Pressure | 0.14503774 | -14.6959 |
| °F | Temperature | 1 | 0 |
| °R | Temperature | 1 | -459.67 |
| °C | Temperature | 1.8 | 32 |
| gpm | Rate | 1 | 0 |
| m³/s | Rate | 15,850.30 | 0 |
| ft³/min | Rate | 7.48052 | 0 |
- Optionally, add an additional column for an adjustment to
formatStringon the tag. - The slope (Factor) & intercept (Offset) columns would contain values to convert to a standard unit of your choosing.
- Disclaimer, don't trust any numbers in the table above, or my math below.
- An operator could select their desired units (from a config screen), whereby session props would contain the desired scaling (via
lookup()function) to convert from their selected unit to a standard unit. Inside of your view, custom properties would contain the same logic - scaling to get from units on the tag to standard units. Combine the session props w/ view props to provide the resultant scaling, all in one expression binding (extra parenthesis added):
ClientValue = (((TagValue * TagFactor) + TagOffset) - ClientOffset) / ClientFactor
(I suppose you could also come up with resultant scaling values as additional custom props).