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Teledyne API - Model 200EH/EM Operation Manual Theory of Operation
195
10.3. PNEUMATIC OPERATION
CAUTION
It is important that the sample airflow system is leak-tight and not pressurized over
ambient pressure. Regular leak checks should be performed on the analyzer as
described in the maintenance schedule, Table 9-1. Procedures for correctly performing
leak checks can be found in Section 11.5.
10.3.1. PUMP AND EXHAUST MANIFOLD
NOTE
Relative Pressure versus absolute pressure. In this manual vacuum readings are given
in inches of mercury absolute pressure (in-Hg-A), i.e. indicate an absolute pressure
referenced against zero (a perfect vacuum).
The gas flow for the M200EH/EM is created by an external pump (Figure 10-10-5) that is pneumatically
connected through a 6.4 mm / 0.25” tube to the analyzer’s exhaust port located on the rear panel (Figure 3-1).
This pump creates a vacuum of approximately 5 in-Hg-A at one standard liter/minute, whi
ch is provided to
various pneumatic components by a vacuum manifold located just in front of the rear panel (Figure 3-1). Gas
flow is create
d by keeping the analyzer’s sample ga
s inlet near ambient pressure, usually by means of a small
vent installed in the sample line at the inlet, in effect pulling the gas through the instrument’s pneumatic systems.
There are several advantages to this external pump / pull-through configuration.
By using an external pump, it is possible to remove a significant source of acoustic noise and vibration
from the immediate vicinity of the sensor. The PMT can act as a “microphone”, amplifying noise and
vibration within the chassis. This is one of the main reasons, why the M200EH/EM has an external
pump.
Pumping heats and compresses the sample air, complicating the measurement process if the pump is
upstream.
Most importantly, however, certain physical parts of the pump itself are made of materials that might
chemically react with the sample gas. Placing the pump downstream of the reaction cell avoids these
problems.
To M200EH/EM
Exhaust Port
Figure 10-10-5: External Pump Pack
04521C (DCN5731)