General MM9 User Manual

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). In this mode, the meter can detect
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.
COMBO MOISTURE METER
USER'S MANUAL
MM9
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 three-
dimensional 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.
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