Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 295)

Theory of Operation Teledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 295
The sample gas is to be made available to the analyzer at a pressure slightly above
ambient but sufficient to allow for a proper flow though the sample lines. The internal
sample system has been designed with minimal restriction allowing sufficient flow at
very low pressure. The input pressure must be reduced and regulated from the process
pressure using a pressure regulator, needle valve, restrictor, critical orifice or any
combination thereof before entering the analyzer. .
Figure 13-7: Internal Pneumatic Flow – Basic Configuration
13.3. FLOW RATE CONTROL
To maintain a constant flow rate of the sample gas through the instrument, the
GFC7001T/GFC7001TM uses a special flow control assembly located in the exhaust
gas line. In instruments with the O
2
sensor installed, a second flow control assembly is
located between the O
2
sensor assembly and the exhaust port. These assemblies consist
of:
 A critical flow orifice.
 Two o-rings: Located just before and after the critical flow orifice, the o-rings seal
the gap between the walls of assembly housing and the critical flow orifice.
 A spring: Applies mechanical force needed to form the seal between the o-rings, the
critical flow orifice and the assembly housing.
13.3.1.1. CRITICAL FLOW ORIFICE
The most important component of this flow control assembly is the critical flow orifice.