Influence On Measurement Accuracy; Technical Terms - PEWA UNITEST TELARIS ERDE Mode D'emploi

4.1 Influence on Measurement Accuracy

Noise voltages present at ground connections may influence the measurement result.
Interference voltage influence is very low for the instrument TELARIS EARTH. A precise
filter suppresses all interference whose frequencies are different with respect to the res-
pective measurement frequency. Together with the possibility to choose between two
measurement frequencies, best measurement results can be guaranteed. During automa-
tic frequency selection mode, TELARIS EARTH selects the measurement frequency with
the lowest, measurable interference voltage. Only carry out manual frequency selection, if
the noise frequency is known. If interference voltages are present influencing the measu-
rement result in spite of the filter, this condition is shown by displaying „Unoise". Further
influence on measurement accuracy is emitted by ratios RH/RE and RS/RE, or absolute
value of RH and RS. If the ratio RH/RE (RS/RE) exceeds the value 1000/1 (10000/1), the
measurement accuracy indicated in the technical data section does no longer apply for
the TELARIS ERDE. This is caused by the fact that the voltage to be measured only amo-
unts to 1/1000 (1/10000) of the voltage present within the measurement circuit. If the
ratio RH/RE (RS/RE) becomes excessive, "D Limit RH (RS)" is shown in the display. The
user should try to realise a better ground connection or earth rod contact to the surroun-
ding earth (e.g. inserting earth rods deeper into the ground, humidify earth).

Technical Terms

Ground: The ground is a conductor within the earth or a foundation being in conductive
connection with the earth (e.g. a foundation ground in concrete).
Reference ground: An area of the earth that is sufficiently distant from the respective
ground such that no noticeable voltages, caused by the grounding current, occur at any
point within this range.
Auxiliary ground (H): Additional ground leading the measurement current for measure-
ment purposes.
Probe (S): An additional ground, preferably an earth rod, which is used as a potential
supply for the reference ground for measurement purposes.
Diffusion resistance of a ground: The resistance of the earth between ground and refe-
rence ground.
Absolute error: Difference between displayed and real measurement variable value.
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