Camille Bauer GOSSEN METRAWATT GEOHM C, Operating Instructions Manual

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6 GMC-I Messtechnik GmbH
Measuring Method and Functional Principle
Earthing resistance is measured with the GEOHM
®
C by means of the
ammeter-voltmeter test method.
The battery powered, potential-free constant power source (quartz-
controlled square-wave generator) delivers constant current of up to
10 mA at a frequency of 128 Hz to the measuring ranges.
In the interest of safety, maximum test voltage at the terminals is limited to
50 V with reference to earth.
Constant test current travels via terminal
E through the earth electrode
whose resistance R
E
is to be measured, through the auxiliary resistor R
H
and finally to terminal H .
The voltage drop which occurs due to earthing resistance R
E
, and which
is measured at terminals ES or E and S , is first fed first to an electronic filter
which is synchronous to the generator, and then to a synchronously
controlled rectifier in order to eliminate influences caused by polarization
voltages and stray alternating currents which are present in the soil to the
greatest possible extent.
The earthing resistance to be measured is proportional to the voltage
drop. It is displayed directly at the LCD in digital format.
Crucial operating conditions are continuously monitored for possible
errors. The presence of interference voltage and values in excess of allow-
able auxiliary earth conductor resistance at the external current circuit are
signaled by means of LEDs. Probe resistance at the voltage circuit is mea-
sured each time a measurement is started. If the allowable value is
exceeded, the appropriate LED lights up.
Excessively low battery voltage and over-ranging are indicated at the LCD.
2 Safety Features and Precautions
The GEOHM
®
C electronic measuring and test instrument has been
manufactured and tested in accordance with safety regulations
IEC 61010-1/EN 61010-1/VDE 0411-1 and EN 61557.
If used for its intended purpose, safety of the operator and the instrument
is assured.
Read the operating instructions carefully and thoroughly before using your
instrument, and observe all instructions included therein.
Attention!
!
Owing to its test voltage of no more than 50 V the tester may not
be used in agricultural facilities.
The measuring and test instrument may not be used:
• If the battery compartment cover has been removed
• If external damage is apparent
• With damaged connector cables and measuring adapters
• If it no longer functions flawlessly
• After excessive stress due to transport
• After lengthy periods of storage under unfavorable conditions
(e.g. humidity, dust, extreme temperatures)
Meanings of Symbols on the Instrument
Indicates EC conformity
Protection class II device
Warning concerning a point of danger
(Attention: observe documentation!)
9 V DC charging socket
for NA102 charging adapter (article no. Z501N)
CAT I I Measuring category 250 V CAT II device
This device may not be disposed of with the trash. Further infor-
mation regarding the WEEE mark can be accessed on the Inter-
net at www.gossenmetrawatt.com by entering the search term
’WEEE’.
!
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