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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.
SNAP SOCKET
CONDUCTIVE RUBBER
SNAP STUD
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.
DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • (781) 821-8370 • Fax (781) 575-0172 • Web Site: http://www.desco.com
TB-2083 Page 3 of 4
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178 • Fax (909) 627-7449
Specifications
Sensitivity Range
Surface Resistivity
Less than 10
Surface-to-Ground
Less than 10
LED Key (from right to left)
1. Red
>10
2. Green
<10
3. Green
<10
4. Green
<10
5. Green
<10
6. Yellow
<10
7. Yellow
>10
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% 10
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).
10
ohms/sq
9
ohms
10
, Meter On, and Battery OK
10
Static Dissipative
9
Static Dissipative
8
Static Dissipative
7
Static Dissipative
6
5
Conductive
9
, 10
© 2002 DESCO INDUSTRIES INC.
10
Employee Owned
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