5TE Operator’s Manual
8. Troubleshooting&Sensor Care
25
Sensor Cleaning
The EC measurement is very sensitive to the presence of non-
conducting contamination on the screws, especially at high
EC. The most common source of contamination is skin oil
from handling the screws traces with bare hands. Figure 3a
and 3b show the simplified electrical circuit resulting from a
finger print on the screw in a low EC soil and high EC soil,
respectively. It is apparent that in a low EC soil, the effects of
contamination are relatively small, because the resistance in
the soil dominates the total resistance. However, in a high EC
soil, the effects of contamination become very large. This
demonstrates the need to keep the screws clean, especially
when the probe is to be used in high EC soil. Contamination
of the screws during handling and shipping prevent the fac-
tory calibration from being valid past 8 dS/m, although the
probes will measure accurately at much higher EC with proper
cleaning and calibration by the user.
Figure 3a: Simplified circuit of con-
taminated probe in low EC (high
resistance) soil. R
total
=101
Ω
,
fingerprint causes 1% error.
Figure 3b: Simplified circuit of
contaminated probe in high EC
(low resistance) soil. R
total
=5
Ω
,
fingerprint causes 25% error
