General MM9 User Manual
COMBO MOISTURE METER
USER’S MANUAL
MM9
Please read these instructions carefully and thoroughly before using the product.
INTRODUCTION
Thank you for purchasing General Tools & Instruments’ MM9
Combo Moisture Meter. Please read this user’s manual carefully
and thoroughly before using the instrument.
The MM9 is designed for use in woodworking, water damage
restoration, building construction and home renovation.
Examples include:
• Checking for moisture and mold on or below the surface of
carpets and subflooring
• Measuring the moisture content of wood, drywall or cement
board before painting, wallpapering, sealing or treating
• Locating water leaks above ceilings, below floors or behind
walls
• Selecting dry lumber
The MM9 can be operated in either of two modes. One is
pinless (non-invasive).
moisture up to 3/8 in. below the surface of drywall, 1/4 in. below
the surface of cement board, and 3/4 in. below the surface of
wood without marring the material with pinholes. 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 powered on.
In this mode, the meter can detect
The meter exploits two physical phenomena to make its pinless
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 top of the MM9 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 threedimensional electric field.
When the top 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.
The MM9 has been calibrated at the factory for use with drywall,
cement board, softwood and hardwood. The capacitance of
wood and the capacitance of building materials are affected
differently by moisture because they have different densities.
The meter compensates for density by adjusting the gain of its
internal sensing circuitry.
1
The MODE button on the front of the meter provides a
convenient way to switch among the four materials. The name of
he material selected appears on the LCD, which displays the
t
abbreviation REL, shorthand for RELative moisture measurement
mode. Below the LCD is a bank of colored LEDs that roughly
mirrors the digital reading above it in bar graph format, with
green indicating “relatively dry” (with a moisture level below
30%), red indicating “relatively wet”, with a moisture level above
70%, and yellow indicating a level between those two values.
An audible out-of-range alarm (beeper) sounds whenever wood
is tested and found to have a moisture content above 16%,
and when drywall or cement board is found to be more than
70% wet.
Although relative moisture readings have no specific value or
accuracy, they are nonetheless useful for quickly comparing the
moisture levels of materials, or the wetness of different areas of
the same material. For example, you can use the meter to locate
the source of a water leak above a ceiling by comparing
readings at various points on it. If the ceiling is level, the point
that produces the highest reading is below the source of the
leak.
Any relative reading can be held by pressing the HOLD button on
the front of the meter. This button makes it possible to make a
measurement in a dark place and display it after bringing the
meter into a lighted area.
The MM9 can also be operated in pin mode
. In this 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 at the top of the MM9 serve as
the electrodes of a conductance meter optimized for measuring
moisture content. In pin mode, the meter displays
measurements in the unit %WME (Wood Moisture Equivalent).
For hard materials like wood, 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 MM9 are only 0.35 in. (9mm) long and
therefore cannot be driven deep into a hard material. For softer
materials like soil, paper or powders, readings are more likely to
reflect the average moisture level of the material between its
surface and the penetration depth of the pins (normally far less
than 0.35 in.).
In pin measurement mode, the color of illuminated bar graph
LEDs indicates the same relative moisture level as in pinless
mode: below 30% for green LEDs, above 70% for red LEDs,
and an intermediate level for yellow LEDs.
To extend battery life in both operating modes, the MM9
automatically 1) dims the brightness of its backlit LCD by
one-half after 15 seconds and 2) powers itself off after 1 minute
of inactivity.
The instrument is powered by a “9V”battery (included on the
back of the blister card).
PRODUCT OVERVIEW
ig. 1 shows all of the controls, indicators and physical features
F
of the MM9. Fig. 2 shows all possible display indications.
Familiarize yourself with the position and function of all
components before moving on to the Setup Instructions
and Operating Instructions.
Fig. 1. The controls,
indicators and
physical features
of the MM9
D
A. Hinged, spring-loaded protective pin cover and pinless
sensor
B. High-contrast, white-on-black LCD (see Fig. 2)
C. LED bar graph; mirrors reading on LCD.
MODE
D.
button.
four target options: drywall, cement board, softwood and
hardwood.
measurement of wood or building material.
for at least two seconds
operation.
E. button.
and held
HOLD
F.
button. “Freezes” and releases readout. Also used to
silence out-of-range alarms.
G. Pin cover latch. Press to open cover, provide access to
measurement pins, and begin operating in pin mode. Closing
the cover automatically initiates operation in pinless
measurement mode.
H. Measurement pins
I. Pin mode
check button
J. Pinless sensor contacts
K. Pin cover spring-loaded hinge
L. Pinless sensor contacts
M. Pinless sensing area
N. Battery compartment
2
In pinless mode
In pin mode
, brief presses cycle through
, a brief press selects WME% moisture
Pressed and held
, re-calibrates pinless mode
Pressed briefly
, powers the meter on.
Pressed
for at least 2 seconds, powers the meter off.
CAL
(calibration)
A
B
C
F
E
G
H
I
J
K
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