Table of Contents
Advertisement
THEORY OF OPERATION
10.2.2. Critical Flow Orifice
In order to accurately measure the presence of low concentrations of O
Sample Air it is necessary to establish and maintain a relatively constant and stable
volumetric flow of sample gas through the instrument. The simplest way to
accomplish this is by placing a Critical Flow Orifice directly upstream of the pump
but down stream from the Absorption Tube.
As the pump pulls against the restricted airway of the orifice a pressure differential
is created. By keeping a sufficiently large the pressure differential across the orifice
(approximately 2:1), a simple and effective control mechanism is established for
maintaining an even flow rate. This has several other benefits:
Fluctuations in the flow rate of the sample gas due to hysteresis in the pump's
operation are smoothed out.
Pressure waves created by the pump's action are filtered out.
The flow rate of the gas is also unaffected by degradations in pump efficiency
due to age.
224
Model 400E Ozone Analyzer
Instruction Manual
in the
3
P/N 04316 Rev: B
Advertisement
Table of Contents
