Edgetech 2000 Series - Page 26

1
Model 2000 Series DewPrime
Dew Poin t Hygrometers
----------- Installation Procedures ----------
must b e give n to the selection of nonhygroscopic sam-
pling materials. (Refer t o Selection of Components at
Lo w De w Points,subsection 2.1 0).
I n general , the most common problem areas that affect
the moisture of a sampled gas are:
1. Lengthof process line and sampleline.
2. Leaks in the process line and sample line.
3 . Adsorption or absoxption of moisture in the process
and sample lines due to the materials of construction .
4. Excessive elbows,tees , valves , or other fittings used
i n the sample lines.
5. Back diffusio n of moisture into a pressurize d system,
particularl y at low dew points.
6. Condensation within the process line and sample line
at high dew points.
7. Diffusio n through the samplin g materials.
The procedures and parts recommende d in this manual
should be used only as a guide in selectin g and designing
samplin g systems. If your application is of a special
nature, callEdgeTech'sSales Application Engineers for
assistance in selectin g sampling components.
2.8 SAMPLING CONFIGURATIONS
A suggested samplin g system for use with the Model
2000 Series DewPrime Dew Point Hygrometer is shown
i n Figure 2-1.A portion of the gas line t o be sample d is
brough t to the hygromete r location from a pressure tap,
either by using a suitable vacuum pmnp or by returning
the sample to a lower pressure point. The flow rate
through this main sampling line should be sufficient to
ensure continuous flushing of the lines in order to provide
fast response times for the sampling system. Usually, a
flow rate ofO.S to 5.0 SCFH (14 to 142 LPH) in a 1/4-
inch line i s adequate; however, this number must be
adjusted wit h the length of the line,the level of absolute
moisture content of the sample, an d the desire d response
time of the sampling system .
A bypass line may be used to increase the main sampling
line velocit y and to improve the overall response time.It
is necessar y that themain sampling line be equipped with
a valve for adjustixlg the sample flow rate . The hy-
grometer's ga s sample is obtained fro m the pressure drop
across the bypass as shown in Figure 2-1.It is desirable
to provide the hygrometer input with a filter, especially if
the gas sample contain s particulate contaminant s . Several
sintered stamles s steel types of suitable filtersare listed
tmde r Recommended Hardware , in subsection 2 . 13. The
filter is considere d a hygroscopic element that will
contribute somelagto the sampling system . In the design
ofhygrometer sampling systems, minimize the number of
components, such as valves, tees , and filters, prior to the
Sensor's input The Sensor output should be connected to
a suitable flowmeasuring device , such as a rotameter or
valve to adjust the flowrate to the recommended range of
0.5 to 5.0 SCF H (14 to 142 LPH).
NOTES
Excessively high sample flow rate s may
cause a los s in the depressio n capability
and unstable operation of the system.
Considerable savings can be obtaine d by
recognizing thatthe sample exhaust lines
and related component s need not be of as
high a quality and as nonhygroscopic as
thoseprior to the hygrometer.
The gas to be sampled must be furnished to the 1/8-27
NPT male ports on the Sensor. Flow ma y pass through
the Sensor in either direction. A sample shut-off valve
may be used on the input side of the Senso r to extract the
sample. Suc h a valve is especially useful when working
'With sample s at high pressures (300 psia max or 211 kg/
cm ) an d whe n opening the Senso r for periodicminor
cleaning.
2.9 PREHEATING SENSOR AND SAMPLE
LINES
· If the dew point of the gas lmder measurement is above
the ambient temperature of the installatio n and sampling
lines , bot h the lines and the Senso r must be preheated.
The samplelines must be furnishe d wit h some type of
heater tape, so that condensate will not form on the
optical components or othe r parts of the Sensor.The
approac h used will var y widely wit h the specific nature of
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