Table 2 Guide to Troubleshooting Measurements
Problem or Unexpected
Observation Behavior
Likely Source of Problem
Analysis
Remedy
Equilibrium
Before concluding that there is an incorrect measurement, make sure that
the system is at equilibrium.
Graph the measurements and wait for
equilibrium.
Sampling point
Consider if the sampling point could be dryer than the rest of the system.
If necessary find a more appropriate sample point
Damage
Corrosion, abrasion
Contaminants can damage the sensor.
Refer to sections: 3 Precautions and 5.2 Sample
conditioning.
Measurement is
dryer
than
is expected.
Needs recalibration
Depending on the application recalibration may be yearly or in 5 years.
Consult with factory.
Equilibrium
Before concluding that there is an incorrect measurement, make sure that
the system is at equilibrium.
Graph the measurements and wait for
equilibrium.
Sampling point
Consider if the sampling point could be wetter than the rest of the system.
If necessary find a more appropriate sample point
Condensation
Refer to the “Measurement is
not changing
” observation below
Damage
Corrosion, abrasion
Contaminants can damage the sensor.
Refer to sections: 3 Precautions and 5.2 Sample
conditioning.
Incompatible materials in system
with low dewpoint.
Refer to section 4.1 Integrity of the materials of the system.
Replace inappropriate materials.
Leaks
Check for leaks around all interconnections.
Tighten fittings. Repair the leaks.
Measurement is
wetter
than
is expected.
Needs recalibration
Depending on the application recalibration may be yearly or in 5 years.
Consult with factory.
Equilibrium
The rate at which the system will reach equilibrium depends on the system
particulars, such at ambient temperature, internal pressure, flow rates,
system materials of construction, surface area of system internals.
Previous experience may be indicative of the
system response time. It is common for systems
to take hours to equilibrate.
Sampling point
Is the sampling point in the direct flow of the system gas, or is it at a dead
end of the distribution system?
Sample in the direct flow.
Contamination
Are there hygroscopic contaminants?
Clean the sensor and install filters.
Out-gassing
Are there materials in the system that could be out-gassing?
Replace the hygroscopic materials.
Leaks
Check for leaks around all interconnections.
Tighten fittings. Repair the leaks.
Large diameter sampling tubing
Larger diameter tubing have larger surfaces.
Use smallest practical tubing diameter, 1/8”
recommended
Measurement is changing
slower
than expected.
Low flow rate
Response time is normally greatly influenced by flow rate, but if the
measurement value is influenced by flow rate there may be a leak.
Flow rate should be greater than
1 LPM.
Measurement is
not
changing
, always shows a
dewpoint close to ambient
temperature.
Condensation
Condensation may have occurred from a slug of water or from previous
conditions where the gas dewpoint was greater than the ambient
temperature. Condensation typically accumulates in filter bowls or other
low points in the system. Then evaporates and produces a high dewpoint.
Drain the condensate and allow the system to dry
down.
Measurement has a
daily
cycle
Thermally induced water vapor
pressure change.
Refer to section 4.3 Temperature dependant equilibrium
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