MKS 1579A, Instruction Manual

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Chapter 9: MFC Sizing Guidelines 1579A/579A
66
Determining the Flow Controller Range
The Type 1579 controller is available in ranges of 50, 100 and 200 slm (N
2
equivalent). To select
the appropriate range, you must determine the flow rate of nitrogen that is equivalent to the flow
rate of the desired gas. Calculate the ratio of the GCF of nitrogen (1.00) to the GCF of the desired
gas (refer to
Appendix C as shown in the following example.
Example:
You need a flow rate of 130 slm of argon (Ar). What range flow controller should you use?
1. Find the Gas Correction Factor of Ar.
The GCF for Ar is 1.39.
2. Insert the GCF of Ar in the following formula:
(x) = (Argon flow rate) x GCF (N2) : GCF (Ar)
where x is the equivalent flow rate of nitrogen (sccm).
( )
( )
( )
( )
Ar slm 130
x
=
1.39
1.00
(x) = 93,5 slm N
2
A flow rate of 93,5 slm of argon will produce a flow rate signal equivalent to 130 slm of N
2
. This
falls within the range of a 100 slm flow controller.
Note
When using a gas with a density higher than nitrogen, be sure that the
control valve full scale range can accommodate the desired flow rate.
Please call the MKS Applications group if you have any questions.
Configurations for Low or High Differential Pressure
The mass flow controllers are designed to operate under certain differential pressure conditions.
Nominal values are listed in
Appendix A, Specifications .
On request however, it is possible to provide special configurations for many applications with low
or high pressure drops, respectively. A typical low pressure application for example is a vaporizer
where liquid material is evaporated at low pressure and reasonable low temperature.