Appendix A. Measurement Considerations
176
Model PM880 Portable Hygrometer User’s Manual
A.1 Choosing a Measurement Site (cont.)
•
Protect the probe cables from excessive physical strain (bending,
pulling, twisting, etc.). In addition, do not subject the cables to
temperatures above 65°C (149°F) or below –50°C (–58°F).
•
Observe the proper cable restrictions for the probes. You can locate the
Moisture Image Series probe up to 915 meters (3,000 feet) away from
the electronics unit with an unshielded twisted-pair cable. The M Series
and TF Series probes require specially shielded cable. You can locate the
M and TF probes up to 600 meters (2,000 feet) from the unit. If you are
measuring pressure with a TF probe, the cable length should not exceed
152 meters (500 feet).
A.2 Moisture/Temperature Probe Considerations
The M Series, TF Series, and Moisture Image Series probes consist of an
aluminum oxide sensor mounted on a connector head. Standard probe
mounts include a protective stainless steel shield.
The probe sensor materials and housing maximize durability and insure a
minimum of water absorbing surfaces in the vicinity of the aluminum oxide
surface. A sintered stainless steel shield is used to protect the sensor from
high flow rates and particulate matter. The end cap should not be removed
except upon advice from GE.
The sensor has been designed to withstand normal shock and vibration. You
should make sure that the active sensor surface is never touched or allowed
to come into direct contact with foreign objects, since this may adversely
affect performance.
Observing these few simple precautions will result in a long and useful
probe life. GE recommends that probe calibration be checked routinely, at
12-month intervals, or as recommended by our applications engineers for
your particular application.
