DP Flow (√ΔP) Calculator
Meter
Calculate from
Q = Qmax · √(ΔP / ΔPmax) at constant density and discharge coefficient. 10 % flow is only 1 % of ΔP — this is why a low-flow cut-off is used and why the turndown of DP meters is limited.
Flow ↔ ΔP ↔ mA
| Flow, % | ΔP, % | mA (linear ΔP) | mA (√ extracted) |
|---|---|---|---|
| 0 | 0 | 4 | 4 |
| 5 | 0.25 | 4.04 | 4.8 |
| 10 | 1 | 4.16 | 5.6 |
| 20 | 4 | 4.64 | 7.2 |
| 25 | 6.25 | 5 | 8 |
| 30 | 9 | 5.44 | 8.8 |
| 40 | 16 | 6.56 | 10.4 |
| 50 | 25 | 8 | 12 |
| 60 | 36 | 9.76 | 13.6 |
| 70 | 49 | 11.84 | 15.2 |
| 75 | 56.25 | 13 | 16 |
| 80 | 64 | 14.24 | 16.8 |
| 90 | 81 | 16.96 | 18.4 |
| 100 | 100 | 20 | 20 |
PLC code (linear ΔP transmitter)
1(* Q = Qmax * SQRT(dP / dPmax); low-flow cut-off 2.0 % of flow *)2IF DP_Pct <= 0.0 THEN3 Flow := 0.0;4ELSE5 Flow := 1.0 * SQRT(DP_Pct / 100.0);6END_IF;7IF Flow < 0.02 THEN8 Flow := 0.0;9END_IF;