Brooks Instrument 5850E - Manual (Page 54)

4-22
Installation and Operation Manual
X-TMF-5850E-MFC-eng
Part Number: 541B102AAG
September, 2009
Section 4 Maitenance &
Troubleshooting
Brooks ® Model 5850E
Restrictors
The Model 5850E Series Mass Flow Controllers use three types of
restrictor assemblies depending on full scale flowrate and expected service
conditions.
1. Porous sintered metal for air equivalent flow rates up to and including
9.5 slpm. The porosity ranges from 1-40 microns. This type of assem-
bly is least expensive and should be used when the gas stream will not
contain any particulate matter.
2. Sintered wire mesh for air equivalent flow rates above 3.5 slpm. These
restrictor assemblies are made from a cylinder of sintered wire mesh
and are easily cleaned if they become contaminated in service.
3. Anti-Clog Laminar Flow Element (ACLFE). This type of restrictor
assembly is used for air equivalent flow rates less than 3.4 slpm. The
ACLFE is much more tolerant to particulate contamination than the
sintered metal assembly. This is especially important when handling
semiconductor gases that tend to precipitate particles. The ACLFE will
also improve accuracy when operating at very low pressures.
Sizing
All Model 5850E Series Restrictor Assemblies are factory adjusted to
provide a 115 mm water column pressure drop for a specific flow rate. This
corresponds to the desired full scale flow rate. A list of restrictor
assemblies used in the Model 5850E Series Mass Flow Controllers is
shown in Table 4-5.
Example:
The desired gas is Silane (SiH4).
The desired full scale flow rate is 200 sccm.
Sensor conversion factor is 0.625 from Table 4-4.
Nitrogen equivalent flow = 200/0.625 = 320 sccm Nitrogen.
In the example above a size P restrictor would be selected. Both the
sintered metal and ACLFE are available for this size. Either type will work
however, since Silane is known to precipitate silicon dioxide particles when
contaminated an anti-clog laminar flow element should be selected for this
application.
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 are being used the restrictor selection
must be based on the Nitrogen equivalent flow rate of the mixture.
Example:
The desired gas is 20% Helium (He) and 80% Chlorine (Cl) by volume.
The desired full scale flow rate of the mixture is 20 slpm.
Sensor conversion factor for the mixture is: