Brooks Instrument SLA5840 - Manual (Page 34)

4-12
Brooks ® Model SLA5840
Section 4 Maintenance
& Troubleshooting Installation and Operation Manual
X-PR-SLA5800-RT-eng
Part Number: 541B120AAG
August, 2009
Sizing
All Delta Class EL Series Restrictor Assemblies are factory adjusted to
provide a specific pressure drop for each flow rate. This corresponds to the
desired full scale flow rate. A list of restrictor assemblies used in the Delta
Class EL Series mass flow controllers/meters are shown in Tables 4-3, 4-4
and 4-5.
Example:
Select a resistor for a Delta Class EL Series SL5850
The desired gas is Silane (SiH4).
The desired full scale flow rate is 200 sccm.
Sensor conversion factor is 0.625 from Table 4-1.
Sensor Nitrogen equivalent flow = 200 x1.000 = 320 sccm Nitrogen
0.625
In the example above a Size P restrictor would be selected from Table 4-3.
Note: If the calculated flow rate is such that two different size restrictors
could be used, always select the larger size.
If a mixture of two or more gases is being used, the restrictor selection
must be based on a Nitrogen equivalent flow rate of the mixture.
Example:
Select a resistor for a Delta Class EL Series SL5850
The desired gas is 20% Helium (He) (Sensor factor = 1.386 and 80%
Chlorine (Cl
2
) (Sensor factor = 0.876) by volume. The desired full scale
flow rate of the mixture is 20 slpm. Sensor conversion factor for the
mixture is:
Sensor Nitrogen equivalent flow = 20 x 1.000 = 21.16 slpm Nitrogen.
0.945
In this example a Size 4 Wire Mesh Assembly would be selected.