TB-2083 September 2010 Page 1 of 4
TECHNICAL BULLETIN TB-2083
Micro Meg™ Pocket Megohmmeter
Operation and Maintenance
Figure 1. 19635 Micro Meg Pocket Megohmmeter
Description
The Desco 19635 Micro Meg Pocket Megohmmeter
is a portable test instrument designed for measuring
both surface and surface-to-ground resistance of
static dissipative and conductive materials. Seven
color-coded LEDs, read from right to left, easily identify
static dissipative and conductive ranges. The µMeg will
test materials with surface resistivity of 1 x 10E5 to 1 x
10E10. This test instrument is ideally suited for Quality
Control and Field Service personnel as well as for use
in routine auditing of your ESD protective materials.
The Micro Meg features simple one-button operation
and a 9V battery for ease of use and maximum
portability. This auto-ranging instrument weighs only
six ounces. The high-impact plastic case ensures
durability despite the meter’s light weight.
The Micro Meg has not been designed to meet ESD
S4.1 test equipment requirements and therefore
measurements obtained with this device may not
agree with measurements taken according to the ESD
S4.1 test procedure. This test instrument is intended
for use only as an auxiliary tool for monitoring surface
resistance performance.
If you are interested in obtaining a meter which does
meet all the test equipment requirements of ESD S4.1,
we recommend our model 19780 Surface Resistance
Test Kit. For more information on this product ask for
Techical Bulletin TB-3014.
Installation
Remove the meter from the carton and inspect for
damage. Each unit should be fully charged and
includes:
1 Micro Meg Pocket Megohmmeter
1 Surface-to-Ground, cord assembly
1 Installed 9V battery
Properly store the megohmmeter and its component
assemblies when not in use.
Operation
The Micro Meg will perform Surface Resistivity
and Surface-to-Ground resistance measurements.
Work surfaces and materials to be tested should be
cleaned prior to testing to ensure that surface dirt and
contamination do not affect results. It is recommended
that non-silicone and non-alcohol based cleaners
such as Desco’s Reztore™ Surface and Mat Cleaner
be used for regular cleaning of ESD protective work
surfaces. When non-ESD surfaces are being used,
Reztore™ Topical Antistat is recommended for
eliminating static charge generation.
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178 • Fax (909) 627-7449
DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • (781) 821-8370 • Fax (781) 575-0172 • Web Site: Desco.com
Made in America
© 2010 DESCO INDUSTRIES INC.
Employee Owned
Figure 2. Cleaning the work surface before testing.
Surface and Surface-to-Ground resistance readings
are indicated by the series of LEDs on the face of the
meter. The LEDs are read from right to left as follows:
1. RED – Meter is on and battery is functioning
2. GREEN – 5 x 10E10
3. GREEN – 1 x 10E9
4. GREEN – 1 x 10E8
5. GREEN – 1 x 10E7
6. YELLOW – 1 x 10E6
7. YELLOW – 1 x 10E5
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Each LED indicates one order of magnitude of
resistance. If the test surface is conductive to less than
10E5, all the LEDs will be lit. If it is neither conductive
nor static dissipative, only the red “On” LED will be lit.
Surface Resistivity Measurements
Surface resistivity measurements are made using only
the meter without the cord assembly. When the white
button is depressed a test voltage of 9 VDC is applied
to the meter’s center electrode. The second resistivity
electrode will supply the resistance bridge and provide
the measurement. To perform surface resistivity tests,
follow these simple instructions:
A. Check battery operation by depressing the white
button on the center of the megohmmeter. The red
“On” lamp at the far right should light to indicate that
the unit is functioning properly.
B. Place the meter on the surface being tested. All
three electrodes should make contact with the surface.
C. Press the white button. The surface resistance will
be indicated by the number of LEDs which light up.
The more lights illuminated, the greater the conductivity
of the surface. The measurement is in ohms/square.
Figure 3. Measuring surface resistivity.
Surface-to-Ground Measurements (RTG)
The Surface-to-Ground feature is best used when
expected results are less than 10E6 ohms, and
when residual voltages can be removed from the test
surface. Residual voltages may cause the two upper
range LEDs to light, resulting in a false reading.
When the Surface-to-Ground cord is plugged in,
voltage is diverted from the center electrode to the
cord in order to measure resistance. When making
Surface-to-Ground tests, follow these procedures:
A. Check battery operation by depressing the white
button. The red “On” lamp will indicate that the unit is
functioning properly.
B. Plug the Surface-to-Ground cord into the left side of
the megohmmeter.
Figure 4. Installing Surface-to-Ground cord assembly.
C. Place the Micro Meg on the test surface.
D. Connect the test cord to the ground-point for the
surface.
E. Press the white button. The LEDs will indicate the
test results. The measurement is in ohms.
GROUND
POINT
WORK SURFACE
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178 • Fax (909) 627-7449
DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • (781) 821-8370 • Fax (781) 575-0172 • Web Site: Desco.com
© 2010 DESCO INDUSTRIES INC.
Employee Owned
Figure 5. Measuring Surface-to-Ground resistance.
F. Unplug the cord when testing is finished.
Battery Operation
Battery function is automatically checked by the unit
when the meter is turned on. If the battery voltage
drops below 8 VDC, the red LED on the far right of the
meter will not light, indicating a “low battery” condition.
Replace battery with a new 9V alkaline battery.
Maintenance
Your Micro Meg will require very little maintenance,
and there are few user-serviceable parts. If your
meter requires service beyond the simple procedures
described below please contact the factory.
Electrode Cleaning
To assure accurate measurements the electrodes
should be kept as clean as possible. A thorough
cleaning at least every 3 months is recommended. The
following is the recommended cleaning procedure:
1. Carefully remove the electrodes from their
snap-jacks using a screw driver or other blunt flat
bladed object. Avoid scratching or bending electrodes.
TB-2083 Page 3 of 4
Figure 6. Cleaning the electrodes.
2. Clean both the snap stud and the electrodes with
a cotton swab soaked in isopropyl alcohol. Check the
rubber centers for wear - the rubber should form a
convex spot on the bottom of the electrode. The three
electrodes will be checked with each annual, factory
calibration. If electrode replacement is recommended,
the customer will be notified with estimated charges
before any changes are made.
Theory of Operation
The Micro Meg measures resistance by setting up a
bridge between two precision 1% resistors of known
value and the surface tested, of unknown value. When
the white button is depressed a test voltage of 9 VDC
is applied to the megohmmeter’s center electrode or
ground cord, depending on the test being performed.
One of the bottom electrodes on the outside of the
meter supplies the resistance bridge. The test voltage
resulting from the bridge is compared to reference
voltages established by six trimming potentiometers.
Two integrated circuits are configured as comparators
to check the voltage from the bridge against the
potentiometers. Based on the setting of each
potentiometer, the appropriate LED is lit.
Specifications
Sensitivity Range
Surface Resistivity Less than 10E10 ohms/sq
Surface-to-Ground Less than 10E9 ohms
LED Key (from right to left)
1. Red >10E10, Meter On, and Battery OK
2. Green 10E10 Static Dissipative
3. Green 10E9 Static Dissipative
4. Green 10E8 Static Dissipative
5. Green 10E7 Static Dissipative
6. Yellow 10E6 Static Dissipative
7. Yellow 10E5 Conductive
Test Sample Size 3" x 1-1/2" or larger
General Characteristics
Power Supply 9 volt alkaline battery (included)
Test Voltage Nominal 9 volts
Electrodes Steel and conductive rubber
Temperature Range
Operating 40°F to 120°F (10°C to 40°C)
Storage 42°F to 110°F (-15°C to +60°C)
Relative Humidity 0% to 99% (non condensing)
Operation Resistance bridge
Readout Seven LEDs
Resolution One order of magnitude
Accuracy ±10% all, except ±20% 10E9,
10E10
Weight 6 ounces
Dimensions 4" x 2.5" x 1.75"
Calibration
The Micro Meg is calibrated to NIST traceable
standards. It may be returned to the factory for
calibration. Contact our Customer Service Department
at 909-627-8178 (Chino, CA) or 781-821-8370
(Canton, MA) for a Return Material Authorization.
Written Purchase Orders are required for calibration
services.
A check on the function of the Micro Meg can be
performed with the following procedure. You will need
1% resistors of the following values: 5 x 10E5 ohms;
5 x 10E6 ohms; 5 x 10E7 ohms; 5 x 10E8 ohms, 5 x
10E9 ohms, and 1 x 10E10 ohms. These precision
resistors will be placed across the two electrodes on
the bottom of the meter (see Figure 7).
For calibrating, when using the resistance value the
LED value is:
LED Value Resistance Value (ohms)
10E10 Green < 5 x 10E10
10E9 Green < 1 x 10E10
10E8 Green < 1 x 10E9
10E7 Green < 1 x 10E8
10E6 Yellow < 1 x 10E7
10E5 Yellow < 1 x 10E6
A. Place the Micro Meg on an insulator (e.g. Teflon or
glass) and press the white test button. Only the first red
LED on the right, marked “On” should be illuminated.
If this LED fails to light, the battery should be replaced
before proceeding.
SNAP SOCKET
CONDUCTIVE RUBBER
SNAP STUD
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178 • Fax (909) 627-7449
DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • (781) 821-8370 • Fax (781) 575-0172 • Web Site: Desco.com
© 2010 DESCO INDUSTRIES INC.
Employee Owned
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B. Place the 1 x 10E10 ohms resistor across the
middle electrode and the side electrode as illustrated
in Figure 7. Press the test button. The second LED
should light. Be sure not to contact the leads or
the buttons as your body’s resistance will affect the
readings. Then use the 5 x 10E9, the 3rd LED should
light. Continue down the line of resistors to test all the
ranges.
Limited Warranty
Desco expressly warrants that for a period of one (1)
year from the date of purchase, Desco Micro Megs will
be free of defects in material (parts) and workmanship
(labor). Within the warranty period, a unit will be tested,
repaired or replaced at Desco’s option, free of charge.
Call Customer Service at 909-627-8178 (Chino, CA)
or 781-821-8370 (Canton, MA) for a Return Material
Authorization (RMA) and proper shipping instructions
and address. Any unit under warranty should be shipped
prepaid to the Desco factory. Include a copy of your
original packing slip, invoice, or other proof of date of
purchase. Warranty replacements will take approximately
two weeks.
If your unit is out of warranty call Customer Service at
909-627-8178 (Chino, CA) or 781-821-8370 (Canton, MA)
for a Return Material Authorization (RMA) and proper
shipping instructions and address. Desco will quote
repair charges necessary to bring your unit up to factory
standards.
Warranty Exclusions
THE FOREGOING EXPRESS WARRANTY IS MADE
IN LIEU OF ALL OTHER PRODUCT WARRANTIES,
EXPRESSED AND IMPLIED, INCLUDING
MERCHANT-ABILITY AND FITNESS FOR A
PARTICULAR PURPOSE WHICH ARE SPECIFICALLY
DISCLAIMED. The express warranty will not apply to
defects or damage due to accidents, neglect, misuse,
alterations, operator error, or failure to properly maintain,
clean or repair products.
Limit of Liability
In no event will Desco or any seller be responsible
or liable for any injury, loss or damage, direct or
consequential, arising out of the use of or the inability to
use the product. Before using, users shall determine the
suitability of the product for their intended use, and users
assume all risk and liability whatsoever in connection
therewith.
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178 • Fax (909) 627-7449
DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • (781) 821-8370 • Fax (781) 575-0172 • Web Site: Desco.com
© 2010 DESCO INDUSTRIES INC.
Employee Owned
RESISTOR
ELECTRODE
Figure 7. Calibration of the Micro Meg
C. Continue this process with each consecutive
resistor, checking to make sure the appropriate LEDs
are illuminated. If all resistors check properly, the unit’s
calibration is verified.
Adjustment
Unauthorized servicing or modifications to the µMeg
will void the product warranty. Servicing should only
be performed by the factory. See warranty section for
repair charges.
