General Tools and Instruments MMD950 - Manual (Page 4)

The distinction between absolute and relative readings is important to
understand. The moisture level measurements made by the remote probe’s
test pins are displayed in units of %WME (Wood Moisture Equivalent)
simultaneously on a 0-99.9 count digital LCD and a 40-LED analog bar graph.
These pin measurements are accurate within 3% of the reading plus 5 digits.
By contrast, readings made by the spherical sensor are simultaneously
displayed with no units on the LCD and on a second scale (called REL) of the
bar graph. Although the readings from the spherical sensor have no accuracy
specification, they are nonetheless useful for quickly comparing the moisture
levels of materials, or the wetness of different areas of the same material. Two
possible uses for the relative readings are:
1. Determining whether two pieces of wood to be joined have roughly the
same moisture content (which means they will dry out at the same rate
without warping).
2. Locating the source of a water leak above a ceiling, by comparing the
REL readings at various points on it. If the ceiling is level, the point with
the highest REL reading is below the source of the leak.
The biggest advantage of the spherical sensor is its ability to sense moisture up
to 4 in. below or behind the surface of a material. The remote probe’s pins can
also sense moisture just below the surface of some materials. However, for
hard materials like wood or concrete, measurements made by pins mostly
represent surface moisture content because: 1) Moisture close to the surface
has a greater effect on a reading than moisture deep below it; and 2) The
10mm (0.4 in.) long pins on the remote probe are too short to be driven deep
into a hard material.
For softer materials like soil, paper or powders, the pin measurements are
more likely to reflect the average moisture level of the material between its
surface and the penetration depth of the pins (usually far less than 0.4 in.).
Other features of the MMD950 include the following:
• Any reading (%WME or REL) can be held by pushing a front-panel button.
Doing so—called locking or “freezing” the reading—makes it possible to
make a measurement in a dark place, hold it, and display it later in a
better-lighted area.
• The 40-LED analog bar graph groups LEDs of three different colors
(green, yellow and red) into low, medium and high moisture bands. Each
readout (%WME or REL) can be accompanied by a beeper that can be
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