Table of Contents
Advertisement
In practice, the sample pressure measurements are made as a differential measurement with
the pump on and then off. This eliminates the effect of any transducer offset. However, since
analyzers share a pump, performing the LIT requires that all analyzers stop monitoring.
Pressures throughout the Vertex M are allowed to stabilize for 30 seconds before taking any
measurements. An LIT causes monitoring to be interrupted for about two minutes because of
synchronization delays. The test is not compatible with shared sample lines.
The use of external filters is mandatory with Vertex M LIT as it is with all Vertex M points.
"Specifications" on page 165 and "Filter Compatibility" on page 165 contain guidance on filter
selection.
8.11.2 Quantitative Performance
The pressure at the pump inlet must be less than -7.0 in Hg or the test will be inhibited. The
sample line must be 4.8 mm ID [thin wall or 0.190 inch ID] and have a length of 90 meters or
less. This supersedes table 8-2 in "Specifications" on page 165.
The total gas flow (transport plus sample) is typically 1.3 liters per minute per point. This results
in a differential pressure of about 1.2 in. Hg with the maximum tubing length. The check valve
increases the differential pressure by an additional 1.0 in. Hg for a total of about 2.2 in Hg.
During characterization the differential pressure must be 0.8 in. Hg or more or a fault will be
issued. During LI testing the differential pressure must be at least 70% of the characterization
differential pressure or more or a fault will be issued. Leaks of 1 mm [0.039 inch] diameter or
larger will cause a substantial decrease in the differential pressure and the generation of a
fault.
The LIT measurement requires that the total pressure variance of the sampled point, the Vertex
M rack and the exhaust outlet must be less than 0.3 in. Hg. for correct operation. See Figure 8-
48 in "Accessing LIT Parameters" below
8.11.3 Software Overview
Automatic LI tests can be scheduled to take place at any of the times when a time weighted
average (TWA) is recorded. TWAs are recorded every eight hours so that up to three LI tests can
be performed per day. As with previous software, the time of the TWA can be shifted up to eight
hours so that the LI test time can be any time of day. The LI test can be disabled on a per-point
basis to permit a rack with LIT to have some tube configurations that are incompatible with LIT.
Buttons are provided to start an LI characterization or an unscheduled test. These two buttons
are on the RS View Authorized Service screen.
8.11.4 Accessing LIT Parameters
A checkbox on the Configure Point screen as highlighted by the red rectangle in Figure 8-48,
enables the selected analyzer to participate in the LIT. By default, all analyzers purchased with
this option will participate. Clearing this checkmark removes the analyzer from the LIT and
prevents the generation of LIT-related faults for the associated point. Otherwise, nuisance
faults may be generated for points with incompatible external components. Examples include
tubes longer than 90m, medium-walled tubing, and shared sample lines.
Vertex M
268
User Manual
Advertisement
Chapters
Table of Contents
