A density meter tells you the mixture is heavy; it does not tell you how many tonnes of solids per hour you are moving. For that you combine mixture density ρm (from an inline meter such as the PS7000) with volumetric flow Q (from a flow meter).
The formulas
| Quantity | Formula |
|---|---|
| Volumetric concentration Cv | (ρm − ρw) / (ρs − ρw) |
| In-situ solids flow Qs (m³/h) | Q × Cv |
| Dry-solids production Pdry (t/h) | Q × Cv × ρs |
| Mass concentration Cw | Cv × ρs / ρm |
| Line velocity v (m/s) | Q / (A × 3600), A = π/4 × ID² |
where ρw = carrier-water density, ρs = dry-solids (grain) density, ID = discharge pipe inner diameter.
Worked example
ρm=1.22, ρw=1.00, ρs=2.50 t/m³, Q=465 m³/h on a DN200 (8″) line:
- Cv = (1.22−1.00)/(2.50−1.00) ≈ 14.6%
- Pdry = 465 × 0.146 × 2.50 ≈ 170 t/h
- Cw ≈ 30%, v ≈ 4.0 m/s
Doing it automatically
The Dredge Production Monitor reads the density meter and flow meter over Modbus and computes all of the above every second, with dashboard, shift totals and CSV history. Set ρw, ρs and pipe ID once in the software. See also dredging applications.