Configuring The Measuring Range - Range Function - Gossen MetraWatt GEOHM C Mode D'emploi

5.4.1 Configuring the Measuring Range – RANGE Function
Automatic Measuring Range Selection
If automatic measuring range selection is used, the instrument selects the
highest possible current it is capable of transmitting from the earth
electrode to the auxiliary earth electrode. This is a constant current with a
square-wave frequency of 128 Hz. The following current values and
resistance measuring values are possible:
Constant Current Resistance Measuring Range
0.01 ... 19.99 Ω
10 mA
0.1 ... 199.9 Ω
1 mA
100 μA 1 Ω ... 1.999 kΩ
100 μA 10 Ω ... 19.99 kΩ
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Note
If a resolution of only 1 Ω occurs with an earthing resistance value
of, for example, 1 Ω, resistance between the earth electrode and
the auxiliary earth electrode is so great that a measuring current of
only 100 μA is possible. Remedy: Drive the auxiliary earth
electrode deeper into the ground or pour a bucket of saltwater
over the auxiliary earth electrode (only effective if the soil is dry).
The auxiliary earth electrode becomes less resistive as a result and
is capable of conducting a larger test current. Probe resistance is
less critical, although a bucket of water may also be helpful if the
soil is dry. Earthing resistance is not influenced by these mea-
sures. However, the earth electrode may not be artificially
watered, because this would simulate optimized conditions for the
measurement.
GMC-I Messtechnik GmbH
Manual Measuring Range Selection
As a rule, you will not need to use manual measuring range selection
unless no measurement value is displayed, or if greatly fluctuating
measurement values occur with automatic range selection. In extreme
cases, superimposed interference voltages may make it impossible for the
automatic range selection function to find a suitable measuring range, and
may result in continuous error messages. A suitable measuring range can
be selected manually in such cases. However, extreme fluctuations in
earthing resistance can only be eliminated by moving the measuring point
to a different location.
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Press the RANGE key.
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Select a suitable measuring range.
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Start the measurement as described above.
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Note
When the measuring range is selected manually, it must be kept in
mind that the specified accuracy values are only valid as of mea-
sured values of at least 5% of the upper range limit (except in the
10 Ω range: separate specification for small values).
The measuring range can be set as high as 50 kΩ by means of manual
measuring range selection.
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