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 • E-mail: [email protected], Internet: www.charleswater.co.uk
PPE-5046.E
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Surface-to-Ground
Measurements (Rg)
The Surface-to-Ground feature is best
used when expected results are less
than 10
6
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 meter.
Figure 4. Installing Surface-to-Ground
cord assembly.
C. Place the
µ
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.
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.
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. If the rubber is worn, replace
electrodes. Otherwise snap the clean
electrodes back onto the meter.
Electrode Replacement
Charleswater Europe offers an
electrode replacement kit for the
:
Meg
(call customer service for information).
Included with each kit are 3 gold plated
electrodes and 3 conductive rubber
electrodes. Replacement electrodes
must be installed correctly to ensure
proper operation. Follow these
instructions carefully:
A. Remove the old electrodes by
placing a screwdriver under the lip of
the gold cap and prying up to remove.
B. Remove the conductive rubber piece
from inside the snap stud.
C. Clean the new electrode assemblies
with isopropyl alcohol.
D. Insert a new conductive rubber
electrode into a new snap socket, with
the widest end down. Be sure the
rubber is pressed in all the way.
E. Carefully trim the rubber electrode
leaving 3.2mm exposed above the
socket.
F. Remove the rubber electrode and
invert it (wide end up).
G. Snap on a new gold electrode
socket over the rubber electrode.
H. The rubber electrode should be
protruding slightly through the hole in
the socket. If not, give the socket a
slight twist until the rubber is exposed.
Figure 7. Replacing the electrodes.
Once you have replaced the electrodes,
you may wish to make a quick
calibration check (see Calibration
Section) to assure that the electrodes
are operative.
Theory of Operation
The
:
Meg measures resistivity 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 meter’s centre 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.
GROUND
POINT
SNAP SOCKET
CONDUCTIVE RUBBER
SNAP STUD
NEW ELECTRODE
SOCKET
NEW RUBBER
CONDUCTIVE
