DP Flow
medium
Converts a differential-pressure reading into a flow rate using a square-root characteristic.
What it teaches
Flow through a restriction raises a pressure drop that grows with the square of the velocity, so recovering flow from that drop means taking a square root — the job every DP flow meter needs done, known on site as square-root extraction. Normalize the reading against full scale, root it, then scale to engineering units. The counter-intuitive part: a quarter of full-scale pressure is half of full-scale flow, not a quarter.
Parameters
| Tag | Direction | Type | Default | Description |
|---|---|---|---|---|
| In_DP | Input | REAL | 25 | Differential pressure from the transmitter |
| Cfg_DPMax | Input | REAL | 100 | Differential pressure at full-scale flow |
| Cfg_FlowMax | Input | REAL | 400 | Flow rate at full-scale differential pressure |
| Out_Flow | Output | REAL | 0 | Computed flow rate in engineering units |
Required behavior
- Out_Flow follows a square-root curve: divide In_DP by Cfg_DPMax, take the square root, and multiply by Cfg_FlowMax.
- Out_Flow is Cfg_FlowMax when In_DP equals Cfg_DPMax, and 0 when In_DP is 0.
- At one quarter of Cfg_DPMax the flow is half of Cfg_FlowMax, not a quarter — that is the square-root characteristic.
- A negative In_DP reads as no flow: Out_Flow is 0, never a positive rate from a reversed reading.
- Out_Flow is 0 when Cfg_DPMax is 0 or less — a bad configuration never drives a flow output.