Michell Instruments XZR200, User Manual

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XZR200 User’s Manual
Michell Instruments 21
APPENDIX B
Appendix B Theory of Operation
The sensor employs a well proven, small Zirconium Dioxide based element at its heart
that does not require a reference gas. This removes limitations in the environments
in which the sensor can be operated with high temperatures, humidity and oxygen
pressures all possible.
Background Physics:
The partial pressure is de fi ned as the pressure of a single gas component in a mixture
of gases. It corresponds to the total pressure which the single gas component would
exert if it alone occupied the whole volume.
Dalton’s Law:
The total pressure ( ptotal) of a mixture of ideal gases is equal to the sum of the partial
pressures ( pi) of the individual gases in that mixture.
Σ
k
i = 1
P i
P total =
From the equation above it can be derived that the ratio of the number of particles
(
ni) of an individual gas component to the total number of particles (ntotal) of the gas
mixture equals the ratio of the partial pressure ( pi) of the individual gas component to
the total pressure ( ptotal) of the gas mixture.
n P i
i
=
P total
total
n
ni
Number of particles in gas i
ntotal Total number of particles
pi Partial pressure of gas i
ptotal Total pressure