Desco Meg Pocket Megohmmeter Service manual

TB-2083 8/02 Page 1 of 4
TECHNICAL BULLETIN TB-2083
:Meg™ Pocket Megohmmeter
Operation and Maintenance
Figure 1. 19635 : Meg Pocket Megohmmeter
Description
The Desco 19635 :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 :Meg will test
materials with surface resistivity of 1x105to 1x1010.
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
: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 :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 :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 :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.
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
mater. The LEDs are read from right to left as follows:
1. RED – >1010, Meter is on and battery is
functioning
2. RED – Less than 1 x 1010
3. GREEN – Less than 1 x 109
4. GREEN – Less than 1 x 108
5. GREEN – Less than 1 x 107
6. YELLOW – Less than 1 x 106
7. YELLOW – Less than 1 x 105
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]
DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com
Made in America
© 2002 DESCO INDUSTRIES INC.
Employee Owned

TB-2083 Page 2 of 4
Each LED indicates one order of magnitude of
resistance. If the test surface is conductive to less than
105, 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 106ohms, 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 :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.
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 :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.
GROUND
POINT
WORK SURFACE
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]
DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com
© 2002 DESCO INDUSTRIES INC.
Employee Owned

TB-2083 Page 3 of 4
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.
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 :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 1010 ohms/sq
Surface-to-Ground Less than 109ohms
LED Key (from right to left)
1. Red >1010, Meter On, and Battery OK
2. Green <1010 Static Dissipative
3. Green <109Static Dissipative
4. Green <108Static Dissipative
5. Green <107Static Dissipative
6. Yellow <106
7. Yellow >105Conductive
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% 109, 1010
Repeatability ±3%
Weight 6 ounces
Dimensions 4" x 2.5" x 1.75"
Calibration
The :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 :Meg can be performed
with the following procedure. You will need 1%
resistors of the following values: 100K, 1M, 10M,
100M, 1G and 10G ohms. These precision resistors
will be placed across the two electrodes on the bottom
of the meter (see Figure 7).
SNAP SOCKET
CONDUCTIVE RUBBER
SNAP STUD
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]
DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com
© 2002 DESCO INDUSTRIES INC.
Employee Owned

TB-2083 Page 4 of 4
A. Place the :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.
B. Place the 10G ohm 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.
Figure 7. Calibration of the : 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 :Meg
will void the product warranty. Servicing should only be
performed by the factory. See warranty section for
repair charges.
RESISTOR
ELECTRODE
Limited Warranty
Desco expressly warrants that for a period of one (1) year
from the date of purchase, Desco :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 PUR-
POSE 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 • [phone] • Fax [phone]
DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com
© 2002 DESCO INDUSTRIES INC.
Employee Owned