Sample Gas Preparation and Delivery DF-745SG
67
8 Sample Gas Preparation and
Delivery
8.1 Introduction
It is important to note key differences in each parameter to ensure a properly
functioning system. Parameters such as flow, pressure, and background gas will
have major effects on total system performance.
8.2 Flow Rate Effects on Sensor Performance
Assuming a leak-free system, flow rate changes will have minimal effects on the
performance of the moisture cell until the flow is so slow that the gas in the
moisture cell chamber is not representative of the process gas being measured.
8.3 Sample Gas Scale Factor
8.3.1 Background Gas Effects on Indicated Flow Rate
If the molecular weight of the background gas is much different from N
2
, the
flowmeter reading is not accurate. The bypass loop flowmeter mounted on the rear
of the DF-700 series Moisture Analyzer is calibrated for use in air (or N
2
). Most
other gases have molecular weights within ± 25 percent of air. Since the required
flow rate is not extremely critical most gases produces reasonably correct readings.
The exceptions are light gases such as Helium and Hydrogen whose flow rates
should be set to approximately one-third that of Nitrogen.
8.4 Flammable Sample Gas
There is nothing within the analyzer sample system that can ignite a flammable
sample gas. However, it is critical to ensure that the sample gas does not escape
from the sample system into the analyzer enclosure, or the room, where ignition is
possible.
Also, the analyzer enclosure can be purged with nitrogen, or the entire Analyzer
can be mounted in a purged enclosure, so that any sample gas that escapes the
plumbing is diluted.
See Section 15 for additional information on the Hydrogen Safety System.
Summary of Contents for NanoTrace DF-745SG
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