Calculated inputs can be used to compensate sensor data from "non-vented" (or "absolute") pressure sensors where the user also has access to suitable (i.e. representative of the non-vented sensor atmospheric conditions and at a similar logging interval) barometric data within their login. The process is as follows:
1. Identify the data source (i.e. input) and units of measurement for the non-vented pressure data that needs compensating
2. Identify the data source (i.e. input) and units of measurement for the barometric pressure data that will be used for the compensation
3. Set up a simple calculated input that
i) converts the units of measurement for one or both inputs so that both inputs are in the same units
ii) subtracts the barometric pressure from the non-vented sensor data
Example:
A user is logging half-hourly readings from non-vented pressure sensor measuring water levels in a lake (Input name = "Raw Lake Level"). The sensor provides readings in cmH2O. The lake is next to a weather station for which the user has access to barometric pressure readings measured in hPa at 1/2hr intervals (Input name = "Thompsons Lake atmospheric pressure").
Step 1: Determine conversion factors for source inputs that convert units of measurement to those required by the output (in this case mH2O):
mH2O = cmH2O x 0.01
mH2O = hPa x 0.010197
Step 2: Create calculated input that subtracts unit-corrected barometric pressure vales from non-vented pressure values:
Return (Inputs.Raw Lake Level * 0.01) - (Inputs.Thompsons Lake atmospheric pressure * 0.010197)