General Tools MMH800 User Manual

4-IN-1 PIN/PAD RH
MOISTURE METER

USER’S MANUAL

MMH800

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

TABLE OF CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 –4

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

What’s in the Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

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

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

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

Operating Instructions . . . . . . . . . . . . . . . . . . . . . . 8 – 10

Measuring Moisture Level . . . . . . . . . . . . . . . . . . . . . 8

Accounting For Temperature and Humidity . . . . . . . 9

Checking Calibration . . . . . . . . . . . . . . . . . . . . . . . . 10

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Maintenance Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Return for Repair Policy . . . . . . . . . . . . . . . . . . . . . . . 12

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INTRODUCTION

Thank you for purchasing General Tools & Instruments’ MMH800 4-in-1 Pin/Pad
RH Moisture Meter. Please read this user’s manual carefully and thoroughly
before using the meter.

The MMH800 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

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

• Locating water leaks in roofs, floors and walls

• Selecting dry lumber

Because it can measure ambient temperature and humidity in addition to
moisture level, the MMH800 is particularly suitable for water damage
restoration projects.

The meter has two LCDs: one displays moisture level and the other—a split­screen display—monitors temperature and humidity. A dedicated front-panel
button selects the default temperature unit (degrees Fahrenheit or degrees
Celsius).

The 4-in-1 part of the meter’s name refers to its ability to measure:

1) temperature; 2) relative humidity; 3) moisture level using a pin sensor; and

4) moisture level using a pad sensor. The meter has both kinds of sensors, with
a pair of pins on top and a split metal pad on the back. Both sensors base their
measurements on the relationship between the moisture content of a material
and its electrical conductivity. The wetter a material, the higher its conductivity.
In both cases, the sensors serve as the electrodes of a conductivity meter
optimized for measuring moisture content.

Which sensor should you use?

It depends on the application. The pad sensor is the only choice for measuring
surface moisture of materials like finished wood, paint or wallpaper that cannot
be marred by pinholes. If measurement accuracy is important, the pin sensor is
the better option because pins can detect moisture below the surface that the
pad sensor cannot.

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However, for hard materials like wood or concrete, the meter’s readings 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
factory-installed pins of the MMH800 are only 0.2 in. (5mm) long and 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 (usually far
less than 0.2 in.). To improve the meter’s overall measurement accuracy, the
MMH800 ships with a 4-pack of pins: two are 0.4 in. (10mm) long, and the
other two are 0.6 in. (15mm) long.

Moisture level readings are displayed as percentages on the upper LCD of the
MMH800, which is factory-calibrated for use with wood/paper and building
materials (concrete, bricks, wallboard, etc.). Because moisture affects the
conductivity of wood/paper and building materials differently, the meter
measures their moisture content using different scales:

• For wood and paper, the moisture level measurement range is
5 to 50%.

• For building materials, the range is 1.5 to 33%.

A front-panel button allows you to switch between the two materials. Display
icons indicate which material is being tested, as well as whether the current
reading is considered low, medium or high for the material. Any reading can be
held by pushing another front-panel button; this feature makes it possible to
make a measurement in a dark place, hold it, and display it later in a better­lighted area. The meter is also equipped with a repeating beeper that beeps
faster with rising moisture level, which makes it easy to detect areas of peak
wetness. The beeper can be disabled without affecting measurements.

The meter also has the following three features:

• It automatically powers off after three minutes of inactivity to extend
battery life

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

• The protective pin cover can be used to check the meter’s
calibration

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