pinless lcd moisture meter with tricolor bar graph mm8

Please read this manual carefully and thoroughly before using this product.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 – 4
Key Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Product Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Setup Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Install Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Measurement Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 – 7
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 – 8
Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Return for Repair Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Thank you for purchasing General Tools & Instruments’ MM8 Pinless LCD
Moisture Meter with Tricolor Bar Graph. Please read this user’s manual carefully
and thoroughly before using the instrument.
The MM8 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 subflooring
• Measuring the moisture content of wood, drywall or masonry before
painting, wallpapering, sealing or treating
• Locating water leaks above ceilings, below floors or behind walls
• Selecting dry lumber
The meter is a non-invasive (pinless) instrument that can detect moisture up to
3/4 in. (19mm) below the surface of the following materials: wallboard,
masonry, hardwood and softwood. 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.
The meter exploits two physical phenomena to make its 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 MM8 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. Displayed readings reflect the
average moisture level of the material between its surface and the electric
field’s maximum penetration of 3/4 in. Moisture closer to the surface has a
greater effect on readings than moisture at the maximum penetration depth.
The MM8 has been calibrated at the factory for use with wallboard, masonry,
hardwood and softwood. 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.
The MODE button on the front of the meter provides a convenient way to
switch among the four materials. The name of the material selected appears on
the LCD. Below the LCD is a bank of colored LEDs that roughly mirrors the
digital reading above it in bar graph format, with green indicating “dry”, red
indicating “wet”, and yellow indicating an intermediate moisture level. An
audible out-of-range alarm (beeper) sounds whenever wood is tested and
found to have a moisture content above 17%, or when drywall or masonry is
found to be more than 70% wet.
Although the LCD displays measurements of drywall and masonry moisture
content as % readings, these are actually relative readings with no accuracy
specification. Despite that shortcoming, relative readings are 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 digital 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.
To extend battery life, the MM8 automatically powers off after two minutes of
inactivity. The instrument is powered by a “9V” battery included in the blister
• Separate settings for drywall, masonry, softwood and hardwood
• 2 in. diagonal high-contrast, white-on-black backlit LCD + 3-color LED
bar graph
• Non-invasive, non-marring detection technology with 3/4 in. (19mm)
maximum sensing depth
• ±4% accuracy on wood
• Calibrates automatically or manually
• Reading HOLD button
• 2-minute Auto Power Off trigger
• Separate out-of-range alarms for wood and building materials
• Low battery indication
• Powered by “9V” battery (included)
Fig. 1 shows all of the controls, indicators and physical features of the MM8.
Fig. 2 shows all possible display indications. Familiarize yourself with the
position and function of all components before moving on to the Setup
Fig. 1.
The controls,
indicators and
physical features
of the MM8
A. High-contrast, white-on-black LCD
B. LED bar graph; mirrors digital
reading on LCD
C. MODE button. Cycles through four
target options: Wallboard, masonry,
softwood and hardwood
D. HOLD button. “Freezes” and
releases digital readout. Also used
to silence out-of-range alarms
E. button. Powers meter on and off
F. Battery compartment
G. Inductive sensing area
Fig. 2. All possible MM8
display indications
A. Moisture reading
B. Low battery indication
C. Drywall mode D. Masonry mode
E. Softwood mode
F. Hardwood mode
G. Held reading indicator
H. Moisture unit. Expressed as a
percentage to make it easy to
compare readings. All readings are
Open the battery compartment at the bottom of the meter (Fig. 1, Callout F) and
push the included “9V” battery inside the compartment with the connector
facing in and following the polarity as indicated on the compartment. Close the
compartment after installing the battery.
To power on the meter, press and hold the button (Fig. 1, Callout E) for at
least three seconds. (To power off the meter, follow the same instruction.)
To measure the moisture level of drywall, masonry, hardwood or
softwood, press the MODE button until the name of the target material
appears on the LCD (WALL is short for drywall). Then scan the material by
gently pressing the inductive sensing area (Fig. 1, Callout G) on the top of the
meter against the material. The LCD will display the material’s moisture content
as a percentage.
Simultaneously, one or more bar graph LEDs will illuminate to place the
material’s moisture level within a spectrum bounded by “dry” and “wet”. The
color of the illuminated LED furthest to the right indicates which % band
contains the material (see the Specifications section on p. 7 for the bands’
To hold a reading, press the HOLD button briefly. The display will show the
held value, along with a lock icon above the % sign. If the reading is above the
alarm limit for that material, pressing the HOLD button will silence the alarm.
For maximum accuracy, press the sensing area against a flat area of a
representative sample of the target material. The sample’s length and width
should be at least as large as the dimensions of the inductive sensing area:
1.6 x 1.6 in. (40 x 40mm).
Ideally, the material should also be at least 3/4 in. thick. That is the meter’s
maximum measurement depth and the thickness it is calibrated for. If your
sample is too thin, the meter will measure material beneath it as well and
produce an inaccurate reading. One way to compensate for thin samples is to
stack them.
Measurements of wood are skewed by two variables: ambient humidity and the
density of the wood species. The best way to compensate for the effect of
these variables is to develop your own moisture level curves, based on your
experience working with different species of wood on a day-to-day basis.
Although the MM8 auto-calibrates each time it is powered on, the meter can be
manually calibrated. Perform a manual calibration whenever the meter cannot
produce a reading, or if multiple measurements of the same sample produce
very different readings.
To manually calibrate the MM8:
1. Power the meter on and hold it in one hand with the top in the air. Make sure
your fingers are not touching or near the inductive sensing area.
2. Press and hold the HOLD button until the display reads 101. Then release the
button; this will change the reading to 102. Wait a few seconds. When the
reading changes to 000, calibration is complete.
Measurement Ranges
0 to 53% for softwood
0 to 35% for hardwood
Relative readings for wallboard and masonry
±4% for hardwood and softwood
3/4 in. (19mm)
Measurement Accuracy
Maximum Sensing Depth
(in wood)
Inductive Sensor Size
1.6 x 1.6 in. (40 x 40mm)
Out-of-Range Alarm Levels >17% for wood
>70% for drywall and masonry
LCD Size
2 in. (51mm) diagonal with three 0.5 in. (13mm) high digits
Display Resolution
Bar Graph Composition
3 each green, yellow and red LEDs
LED Bands
For drywall and masonry: green = 0 to 30%,
yellow = 31 to 70%, red = >70%
For wood: green = 5 to 14%,
yellow = 15 to 17%, red = >17%
Auto Power Off Trigger
2 minutes of inactivity
Operating Temperature
32° to 104°F (0° to 40°C) @ 5 to 95% R.H.
Storage Temperature
14° to 122°F (-10° to 50°C)
Power Source
6.3 x 2.8 x 2.9 in. (160 x 70 x 73.5mm)
4.7 oz. (132g) without battery
(1) “9V” battery (included)
In the U.S, General warrants its instruments and accessories, and digital tools against
defects in material or workmanship for one year from the date of purchase unless
otherwise stated on the packaging, manual, and/or marketing materials. General also
warrants its non-digital tools products against defects in material or workmanship on a
limited lifetime term. The company will replace or repair the defective unit, at its option,
subject to verification of the defect.
This warranty does not apply to defects resulting from abuse, neglect, accident,
unauthorized repair, alteration, or unreasonable use of the product.
Any implied warranties arising from the sale of a General product, including but not
limited to implied warranties of merchantability and fitness for a particular purpose, are
limited to the above. General shall not be liable for loss of use of the product or other
incidental or consequential damages, expenses, or economic loss, or for any claim of
such damage, expenses, or economic loss.
State laws vary. The above limitations or exclusions may not apply to you.
Every effort has been made to provide you with a reliable product of superior quality.
However, in the event your instrument requires repair, please contact our Customer
Service to obtain an RGA (Return Goods Authorization) number before forwarding the
unit via prepaid freight to the attention of our Service Center at this address:
General Tools & Instruments
75 Seaview Drive Secaucus, NJ 07094 212-431-6100
Remember to include a copy of your proof of purchase, your return address, and your
phone number and/or e-mail address.
75 Seaview Drive Secaucus, NJ 07094-1806
PHONE (212) 431-6100 FAX (212) 431-6499 TOLL FREE (800) 697-8665
MM8 User’s Manual
Specifications subject to change without notice
MAN# MM8 02/23/18