Brooks Instrument SLA5840 - Manual (Page 30)

4-8
Brooks ® Model SLA5840
Section 4 Maintenance
& Troubleshooting Installation and Operation Manual
X-PR-SLA5800-RT-eng
Part Number: 541B120AAG
August, 2009
4-5 Restrictor Sizing
The restrictor assembly is a ranging device for the sensor portion of the
controller. It creates a pressure drop which is linear with flow rate. This
diverts a sample quantity of the process gas flow through the sensor. Each
restrictor maintains a ratio of sensor flow to restrictor flow, however, the
total flow through each restrictor is different. Different restrictors (active
area) have different pressure drops and produce controllers with different
full scale flow rates. For a discussion of the interaction of the various parts of
the controller, you are urged to review Section 3-2, Theory of Operation.
If the restrictor assembly has been contaminated with foreign matter, the
pressure drop versus flow characteristics will be altered and it must be
cleaned or replaced. It may also be necessary to replace the restrictor
assembly when the mass flow controller is to be calibrated to a new flow
rate. Restrictor assembly replacement should be performed only by trained
personnel. Consult factory/Service Center.
Restrictors
The mass flow controller/meter uses different types of restrictor
assemblies depending on full scale flowrate and expected service
conditions.
For Models SLA5840 RT
1. Wire mesh for Nitrogen equivalent flow rates above 3.4 slpm. These
restrictor assemblies are made from a cylinder of wire mesh and are easily
cleaned if they become contaminated in service.
2. Anti-Clog Laminar Flow Element (ACLFE) or Sintered Metal Restrictor
Assemblies are used for Nitrogen equivalent flow rates less than 3.4 slpm.