Endress+Hauser SpectraSensors SS2100i-1, Обзорное руководство

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SCS Overview Manual 4
–
1
4 - V
ALIDATION OF
T
RACE
M
OISTURE
M
EASUREMENTS
The information contained in this chapter is provided for systems designed to
detect moisture.
Validation Methods
SpectraSensors uses one of two methods to validate low moisture
measurements; a permeation validation system and a dynamic dilution.
Permeation validation systems provide a convenient and reliable method of
validating the performance of the analyzer, without the need for elaborate
blending systems and certified standards that might be impossible to obtain in
the field. The analyzer accuracy and repeatability is not based on, certified or
tested using the installed permeation device, however. SpectraSensors has
found that permeation devices generally do not generate more stable,
repeatable or accurate trace moisture mixes than the dynamic dilution stations
used in our factory to calibrate the analyzer.
In a dynamic dilution, a certified blend of gas can be diluted using precision
flow controllers to produce the desired concentration of trace moisture in the
actual sample gas.
Permeation Validation for Trace Moisture
(0-10 ppm H
2
O)
The concentration measured during calibration, C
p
, is related to the certified
permeation rate of the device, R
p
, by a system constant, K
p
, using the
equation:
K
p =
C
p/
R
p
This equation requires that the following conditions be met:
•
Sample temperature is stable and equal to the temperature at
calibration
•
Sample flow is stable and equal to the flow at calibration
•
Sample pressure at the permeation device is stable and equal to the
pressure at calibration.
The permeation rate and resultant water content of the validation
flow have been carefully calibrated at the factory (refer to the
analyzer system drawings for the calibrated output of the
validation flow). DO NOT adjust the pressure regulator, needle
valve, flow controllers or temperature of the sample conditioning
system or the calibration of the validation flow will be lost. Contact
Service if you suspect the settings of the sample conditioning
system have been altered. Refer to “Service Contact” on page
B-5.