Cosa-xentaur Xentaur LPDT Manuel d'utilisateur télécharger pdf (Page 12)

Section 2: Sensor and Sampling Techniques

page 5

diameter of tubing, number of interconnecting fittings, dead

space in tubing and manifolds; will influence the measure-

ment value and response time.

The high capacitance HTF™ sensors can be installed either

directly in the line to be sampled (in-situ), or in a slip stream

of a sample system (extractive).

To assure a long and accurate performance of the sensor, it

should be protected from contaminants such as liquids

(water, oil etc.), and particulates. The sintered stainless steel

sensor encapsulation protects from particulates larger than

100 microns, finer particulates (e.g. from degraded desic-

cant or rust) should be filtered with a particulate filter with

suitable capability, do not use hygroscopic filter materials.

2.3.1 In-situ Installation

In-situ installation is recommended only for measurements

where the gas pressure is expected to vary little, the gas is

expected to be free of contaminants, the gas temperature is

within the operating specifications of the sensor, and there is

no chance of liquids coalescing. Examples of applications

suited for in-situ installations are: pure gases, output of des-

iccant dryers (for instrument air), glove boxes, etc. For most

other applications in-situ installation should be avoided for

the following reasons:

• Sample conditioning is almost always necessary to

avoid exposure of the sensor to liquid water and other

contaminants, such as hydrocarbons, which may dam-

age the sensor or affect accuracy over time.

• Variations in line pressure affect the reading of the sen-

sor because dewpoint varies with pressure.

• If the gas line is under pressure, it is more likely that

water condensation occurs which may damage the sen-

sor.

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Cosa-xentaur Xentaur LPDT Manuel d'utilisateur Page 12