Ingersoll-Rand HC-103, User Manual

Page: 82 / 128

INSTRUCTION MANUAL
Sahara Moisture Transmitter
Reference IR-085 Rev 3
Page 14 of 16 01/10/2014
VIII. Helpful Information (continued)
4. The probe is very rapid, is insensitive to temperature and flow rate and
measures the vapor pressure of water only. If the above effects are noted, then
they are almost always the result of the system itself and not the sensor.
a. Pressure
i. It is generally advantageous to operate at the highest possible
pressure, especially at very low moisture concentrations. This
minimizes wall effects and will result in higher dew points with
subsequent increased sensitivity.
b. Response Time
i. The response time is, in general, limited by the response time of the
WHOLE SYSTEM to moisture changes. Water vapor is adsorbed
tenaciously in many materials. A large, complex processing system
can take several days to “dry down” from atmospheric moisture levels
to dew points of less than -75

F. Even simple systems consisting of
several feet of stainless steel tubing and a small chamber can take an
hour or more to dry from dew points of +40

F to -95

F. The rate of
equilibrium of the system will be dependent on the flow rates,
temperature, materials of construction, and the system pressure.
ii. An increase in flow rate and temperature will decrease the response
time of the whole system.
c. Temperature
i. It is recommended that the ambient temperature be at least +50

F
higher than the measured dew point (to a maximum of 150

F).
d. Flow Rate
i. If the dew point of a system changes as the flow rate changes, then it
can be attributed to inequilibrium (i.e. the system is off-gassing or
leaking). With moisture leaking in a system (either a physical leak or the
release from the walls of previously adsorbed moisture), an increase in
flow rate should result in a lower vapor pressure and, hence, a lower
dew point due to the dilution of the secondary moisture by the main gas
stream.