AMI Analyzer Manual
Installation and Operation
10
A note on analyzer linearity:
Since the analyzer generates a relative measurement, it is not possible to characterize its linearity any
better than by using a series of primary standard gases to verify its performance. Since these gases are only
specified to be 1% accurate, we can’t specify the analyzer as being any better than that, hence the 1%
linearity spec. Experience indicates that in fact over many measurements we do better than 1%, but we
can’t guarantee it since there is no way of verifying that we really do so. For particular purposes, there are
software adjustments that we can make that provide specific curve changes so that we can exactly match
what a particular set of gases say, however these are by default left in their standard (linear) position. If for
some reason you absolutely do have to match the analyzer to a set of standard gases, we can help you do
so using our User Interface software package. We do recommend against doing this save as a last resort.
Atmospheric pressure effects:
The sensor is not particularly sensitive to changes in ambient pressure – a 5psi ambient change will change
its reading by 0.4% of its value (i.e. 20.9% at 15psia will read about 20.8% at 10psia). Atmospheric pressure
changes are usually less than 1psi, so the error due to this will be unnoticeable. Greater changes will be
noticed from humidity effects when measuring air – at 110
º
F you can have up to 3% humidity, which
effectively reduces the oxygen concentration by the same proportion, to 20.3%.
High oxygen level gas hazards:
High oxygen level gas such as 95% oxygen in nitrogen is a very strong oxidizing agent. Treat it as if it is pure
oxygen, and familiarize yourself with the rules for handling pure oxygen before attempting to use it. In
particular, all tubing used must be suitable for oxygen service, and if you are using a high pressure span gas
cylinder, you MUST use a dual stage regulator with stainless steel diaphragms on it. Any sudden failure of a
regulator may allow enough temperature rise through adiabatic compression to ignite virtually anything,
including stainless steel tubing and an AMI analyzer.
