E C O P H Y S I C S Practical hints
CLD 780 TR / July 2000 97
7.5 Influence of atmospheric pressure fluctuations on the measuring
signal
A change in mass flow rate through the reaction chamber effects the
measured signal. The use of a critical orifice flow restrictor causes the
mass flow to vary only as a function of inlet pressure and the type of gas
(when monitoring ambient atmosphere, this is always air of course). The
inlet pressure for the CLD 780 TR is always the ambient atmospheric pres-
sure (sample gas and cal. gas must always be supplied to the inlet at at-
mospheric pressure by using a bleed line).
To minimize any possible influence of ambient pressure fluctuations on the
measurement data, it is suggested that rather than four calibrations be
made per day instead of just one.
For application where the ambient pressure varies rapidly (i.e. in airborne
platforms), it is recommended that a CLD 780 TR fitted with Option 2 (By-
pass system) be used.
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