Omega RH650 User Manual page 5

• Electronics manufacturing. Alerts provided by the low RH alarm of the RH650 can mitigate
the risk of damaging high-voltage static discharges.
Water damage remediators will also make use of the RH650's ability to calculate an
environment's mixing ratio (often represented by the unit GPP, or grains per pound). GPP is a
more useful moisture metric than RH to water damage remediators. Using RH alone, a remediator
might unknowingly introduce moist air—with a low RH but a high GPP—during a job's drying
phase. The RH650's atmospheric pressure sensor makes its calculations of GPP—as well as
dew point and vapor pressure—more accurate than those of competitive units which use
standard atmospheric pressure at sea level.
Another parameter of interest to water damage remediators is the moisture level of a substance
(typically, wood or building materials). The RH650 can measure this parameter using either a
pinless (non-marring) or pin-type (penetrating) probe; the meter includes both kinds of probe.
Operating in internal moisture mode, the meter uses a non-invasive (pinless) sensor on the back
of the unit to detect moisture up to 3/4 in. (20mm) below the surface of wallboard, masonry,
hardwood and softwood. It infers the level of moisture from the material's capacitance, which the
meter measures by gauging its effect on an electric field that the meter generates each time it is
operated in internal moisture mode.
In internal moisture mode, the meter exploits two physical phenomena to make its
measurements:
1. The linear relationship between a solid material's moisture level and its dielectric
constant—and therefore its capacitance.
2. The so-called fringing-field effect—the slight spreading of the electric field produced by
current flowing between two electrodes when both electrodes are on the same side of a
material.
Behind the back cover of the RH650 are two metal plates. When the meter is powered on, the
plates are given small and opposite charges. The potential difference causes current to flow,
creating a three-dimensional electric field.
When the back of the meter is placed against one side of a material with moisture on or slightly
below its surface, the increased capacitance of the material distorts the electric field to an extent
that can be sensed (as a change in flux over the sensing area) and measured. Displayed readings
reflect the average moisture level of the material between its surface and the electric field's
maximum penetration of 3/4 in. Moisture closer to the surface has a greater effect on readings
than moisture at the maximum penetration depth.
In external moisture mode, the meter bases its measurements on the relationship between the
moisture content of a material and its electrical conductivity. The wetter a material, the higher its
conductivity. The two replaceable steel pins of the included external probe serve as the
electrodes of a conductance meter optimized for measuring moisture content. The meter displays
measurements in the unit %WME (Wood Moisture Equivalent).
For hard materials like wood or concrete, the meter's readings largely reflect surface moisture
content because: 1) Moisture close to a surface has a greater effect on a reading than moisture
deep below it; and 2) The pins of the external probe are only 3/8 in. (10mm) long and cannot be
3