Device that measures a pressure gradient along a fluid column
| (1) | G_p = \frac{dp}{dl} |
The pressure gradient model can be correlated to fluid velocity as:
| (2) | G_p = a + b_l \, q^{n_l}+ b_t \, q^{n_t} |
In smaller range of flowrate variations this can be simplified to:
| (3) | G_p = a + b \, q^n |