Data Reduction
Convert ASP sensor outputs to relative or absolute settlement
Outputs
The ASP communicates digitally via an RS485 BUS. Your data logger will recall measurements from the ASP via an ASCII protocol or MODBUS RTU.
The following provides details on each of the possible outputs:
Distance
The ASP nodes carry out onboard conversion of pressure to mm head. Change in elevation is relative to the reference sensor(s). To calculate the current elevation of a measurement node, the following calculations are used:
Change in Relative Elevation
Fixed Reference Sensor
If the elevation of the reference sensor is assumed to be fixed:
Δeₙ = Δₙ - Δᵣ
Where:
-
Δeₙ= change in relative elevation of a given node -
Δₙ= n₁ - n₀ = current reading at node n minus initial reading at node n -
Δᵣ= r₁ - r₀ = current reading at reference sensor, or the mean of readings from multiple reference sensors minus initial reference reading
Derived Reference
If the elevation of the reference is derived:
Δeₙ = Δₙ - Δᵣ + Δd
Where:
-
Δeₙ= change in relative elevation of a given node -
Δₙ= n₁ - n₀ = current reading at node n minus initial reading at node n -
Δᵣ= r₁ - r₀ = current reading at reference sensor, or the mean of readings from multiple reference sensors minus the initial reading at the reference sensor(s) -
Δd= d₁ - d₀ = current reading of the external reference minus the initial reading
Absolute Elevation
To calculate the absolute elevation of a measurement node:
Eₙ₁ = Δeₙ + Eₙ₀
Where:
-
Eₙ₁= Current reduced level of a given node -
Δeₙ= change in relative elevation as described above -
Eₙ₀= Initial reduced level of node at time of installation
Always record initial elevations (Eₙ₀) during installation and the baseline reading period to enable accurate absolute elevation calculations.
Voltage
Voltage received by each sensor during measurement.
This provides useful troubleshooting metric, and often a better indicator of reducing battery power than the power recorded by the data logger itself.
Temperature
Temperature at each sensor in degrees Celsius.
While temperature compensation is carried out during the Distancemeasurement, the temperature reading confirms stable temperature across the system and identifies any physical issues that may be impacting the measurement performance.
Status
Numerical code indicating measurement status.
| Status | Osprey Error Code | Description |
|---|---|---|
| 0 | N/A | Measurement OK |
| 1 | -99 | Measurement Not Ready |
| 2 | -98 | Pressure value outside threshold |
| 3 | -97 | Sensor reports an internal error |
| 4 | -96 | Insufficient power |
Support
For further assistance with data collection and interpretation, please contact:
-
Support Portal: support.ospreymeasurement.com