Influence On Measurement Accuracy - BEHA UNITEST TELARIS ERDE 8986 Manual De Instrucciones

Influence on Measurement Accuracy

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 in-
terference whose frequencies are different with re-
spect to the respective measurement frequency. To-
gether with the possibility to choose between two
measurement frequencies, best measurement re-
sults can be guaranteed. During automatic fre-
quency selection mode, TELARIS EARTH selects
the measurement frequency with the lowest, mea-
surable interference voltage. Only carry out manu-
al frequency selection, if the noise frequency is
known. If interference voltages are present influ-
encing the measurement result in spite of the filter,
this condition is shown by displaying „Unoise". Fur-
ther 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 accura-
cy 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
amounts 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 surrounding earth (e.g. inserting earth rods
deeper into the ground, humidify earth).
22
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 suf-
ficiently distant from the respective ground such
that no noticeable voltages, caused by the ground-
ing current, occur at any point within this range.
Auxiliary ground (H): Additional ground leading the
measurement current for measurement purposes.
Probe (S):An additional ground, preferably an earth
rod, which is used as a potential supply for the ref-
erence ground for measurement purposes.
Diffusion resistance of a ground: The resistance
of the earth between ground and reference ground.
Absolute error: Difference between displayed and
real measurement variable value.