Characterizing a filter with a pressure controller and mass flow meter

A common application of Alicat’s mass flow and pressure devices is the characterization of a static device with pressure drop, such as a filter or static orifice. Filters and static orifices have pre-defined curves for the relationship between pressure and flow rate. A customer will most likely want to develop this curve or test a specific filter to ensure it agrees with the published data.

In this case, it is useful to control pressure while measuring flow rate or vice versa. The most common technique for filter characterization is controlling the mass flow rate while measuring the differential pressure.

Using differential pressure control to characterize a filter

An Alicat differential pressure controller is used to characterize a filter’s flow against a pressure drop curve. A 15 PSID pressure controller is used to set the pressure drop across the filter, while a 10 SLPM mass flow meter is used to measure the flow rate required to generate that pressure drop. An advantage of this setup is that serial input of the desired pressure drop allows the user to run canned scripts at known time intervals, while a common control interface is used for both pressure and flow.

In the setup above, the mass flow meter is placed downstream of the pressure controller and filter, but it can also be placed upstream as mass in equals mass out.