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.
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.
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
Snap Socket
Conductive Rubber
Snap Stud
Unit 17. Millbrook Business Park, Sybron Way • Crowborough, East Sussex TN6 3JZ United Kingdom
Phone: 00 44 (0) 1892-665313, Fax: 00 44 (0) 1892-668838 • Internet:
PPE-5046.E
Page 2 of 3
© 2011 CHARLESWATER LTD.
Figure 6. Cleaning the electrodes.
