General Tools MMD900 User Manual

PIN/PINLESS DEEP SENSING

MOISTURE METER

WITH REMOTE PROBE

USER’S MANUAL

MMD900

Please read this manual carefully and thoroughly before using this product.

TABLE OF CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 – 5

Key Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

What’s in the Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Product Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 –7

Setup Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Install Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Operating Instructions . . . . . . . . . . . . . . . . . . . . . . 8 – 12

Measuring Moisture Levels . . . . . . . . . . . . . . . . 8 – 10

Advanced Setup Instructions . . . . . . . . . . . . . . 10 – 12

Checking Calibration . . . . . . . . . . . . . . . . . . . . . . . . 12

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Maintenance Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Return for Repair Policy . . . . . . . . . . . . . . . . . . . . . . . 15

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Thank you for purchasing General Tools & Instruments’ MMD900 Pin/Pinless
Deep Sensing Moisture Meter with Remote Probe. Please read this user’s
manual carefully and thoroughly before using the meter.

The MMD900 is designed for use in woodworking, water damage restoration,
building construction and home renovation. Examples include:

• Checking for moisture on or below the surface of carpets and
sub-flooring

• Measuring the surface moisture content of wood, drywall or concrete
before painting, wallpapering, sealing or treating

• Locating water leaks above ceilings, below floors or behind walls

• Selecting dry lumber

The meter senses the moisture level of a material using either of two
techniques:

1. Inferring the material’s electrical conductivity from the current flow

induced between a pair of steel pins placed on or into the material. The
wetter a material, the higher its conductivity. The MMD900 is equipped
with two pairs of test pins—one pair on the top of the instrument and the
other at the end of a cable and remote probe that can fit in tighter spaces.

2. Measuring the change in the material’s capacitance produced by the

slight spreading of a local electric field generated by the meter. When
the meter is powered on, two plates inside the back of the MMD900’s
housing are charged with opposite polarity and pulsed at a high
frequency. This causes current to flow, creating a three-dimensional
electromagnetic wave at radio frequency that extends about 2 in.
(50mm) perpendicular to the meter. When the back of the meter is
placed against a wet material, the increased capacitance of the material
distorts the wave’s electric field to an extent that can be measured. The
distortion—called the fringing field effect—is proportional to the
material’s moisture level.

WHICH SENSOR SHOULD YOU USE?

It depends on the application. The pinless (capacitive) sensor is the only choice
for estimating the surface or internal moisture level of materials like finished
wood, paint or wallpaper that cannot be marred by pinholes. If accurate
readings are important, the pin sensor is the only option because the pinless
sensor can only provide relative readings.

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The distinction between absolute and relative readings is important to
understand. The moisture level measurements made by either pair of test
pins—on the instrument or on the remote probe—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. Pin measurements are accurate within
3% of the reading plus 5 digits.

By contrast, readings made by the pinless sensor are simultaneously displayed
with no units on the LCD and on a second scale (called REL) of the bar graph.
Although the pinless readings 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 pinless sensor is its ability to sense moisture up
to 2 in. below or behind the surface of a material. The stainless steel test pins
of the MMD900 can also sense moisture just below the surface of some
materials. However, for hard materials like wood or concrete, measurements
made by the meter’s test 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 pins of the MMD900 are too short to be
driven deep into a hard material. The pins at the top of the meter are 15mm
(0.6 in.) long and the pins on the remote probe are 10mm (0.4 in.) long.

For softer materials like soil, paper or powders, 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 0.6 or 0.4 in.).

Other features of the MMD900 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.

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• 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 programmed to
sound in different ways in response to different moisture levels or operations.
The correlations make it easy to use sight and/or sound to pinpoint areas of
peak or relative wetness. The beeper can be disabled without affecting
measurements.

• An auto power off function that can be triggered by three, five or 10 minutes
of inactivity.

• The protective cover for the meter’s test pins can be used to manually check
the meter’s calibration. Alternatively, the meter can automatically check its
calibration each time it is powered on.

• A display icon indicates when the meter’s 9V battery is low on charge.

KEY FEATURES

• Two measurement modes: Pin (conductivity-based) and pinless
(based on the fringing field effect)

• Two sets of test pins: on top of the meter and at the end of 46 in. remote
cable

• Pin measurement accuracy of ±3%

• Pinless mode measurement depth of 2 in. below surface

• Displays %WME and relative readings simultaneously on two displays:
0 to 99.9 count jumbo LCD with 0.9 in. (23mm) digits, and 40-dot tri-color
LED bar graph

• Manual or automatic calibration checking

• Data hold (display lock or “freeze”) function

• User-programmable beeper function, backlight function and auto power off
time

• Low battery warning

• Includes two pairs of replacement test pins

• Spare pins storage compartment

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