Veris Technologies 3150 Soil EC Mapping System - Trouble-shooting - Manual (Page 9)

B. Testing Coulter-Electrode continuity
1. Place ohmmeter lead on terminal wire bolt and other lead on disk blade. Rotate
blade ¼ turn. If readings are consistently above 2 ohms, check for excessive
corrosion at the coulter blade mounting bolts, or the terminal located near the
coulter pivot. Make sure that high ohm readings are not due to poor contact
between blade and ohmmeter lead. Re-test holding lead firmly against edge of
blade, removing rust or paint if necessary.
2. If ohms jump over 2 ohms when the blade is rotated, and you were careful to
maintain good contact between the lead and the blade, the problem is likely inside
the hub. Because electrical signals cannot be sent consistently through the coulter
bearing, Veris has designed a more reliable path for the EC signal to travel. A
special hub with a spring plunger presses against the spindle of the coulter, serving
as a commutator. Shown below is a cut-away view of the hubcap and plunger
assembly. When ohm readings jump during blade rotation, it is due to the greased
rollers on the bearing making intermittent and inconsistent contact. See
Maintenance and Service procedure #4: Spring Plunger adjustment and
replacement on adjusting and replacing spring plungers.
Figure 3.7
C. Testing Coulter-Electrode isolation
If continuity tests show no excessive resistance on any channel, yet erratic soil EC
readings continue, or if EC readings do not drop to
–1 when unit is out of the soil, it is
possible that the channels are not isolated. This could be the result of a pinched wiring
hubcap
commutator
coulter spindle