Table 1.

Relative resistance changes caused by particles passing a sensing orifice. D and L are the diameter and length of the sensing orifice, d is the diameter of the particle.

Relative Particle Diameter (d/D)	Relative Resistance Change (ΔR/R)
Infinite smaller diameter [38]	$\frac{d^3}{D^{2}L}$
Smaller diameter [39]	$\frac{d^3}{D^{2}L}\left[\frac{D^2}{2L^2}+\frac{1}{\sqrt{1+{(D/L)}^2}}\right]F\left(\frac{d^3}{D^3}\right)$
Medium diameter [40,41]	$\frac{d^3}{D^{2}L}\cdot \frac{1}{1-0.8{(d/D)}^3}$
Larger diameter [42]	$\frac{D}{L}\left[\frac{\arcsin (d/D)}{\sqrt{1-{(d/D)}^2}}-\frac{d}{D}\right]$

Note: $F(x)=1+1.264x+1.347x^2+0.648x^3+4.167x^4$ [43].