Knowledge Base

If a failure of any vibrating wire transducer or the electrical cable is suspected, the following steps can be followed. The transducers themselves are sealed and cannot be opened for inspection. The “Troubleshooting Flowchart” (below) should also be followed if any instrument failures are suspected.

The steps below and the Troubleshooting Flowchart are applicable generally to any vibrating wire instrument.

STEP 1

Before any of the following steps are followed, the portable data logger should be used to verify the stability of the reading and the audio signal from the portable logger should be heard. An unstable (wildly fluctuating) reading from a transducer or an unsteady audio signal are both indications of possible problems with instruments or their related electrical cables. If a portable data logger is giving faulty readings or audio signals from all transducers, a faulty readout unit must be suspected. Another readout unit should be used to check the readings from the transducers and itmsoil Instruments Ltd. should be consulted about the faulty readout unit.

STEP 2

The resistance across the two conductors of the electrical cable should be checked. This can be done using a multimeter device across the two exposed conductors if the cable has not been connected to a terminal cabinet, or can be done just as easily across the two conductors if the instrument has been connected to such a terminal (or datalogger). The resistance across the two conductors should be approximately of the order of 120Ω to 180Ω. The majority of this resistance will come from the transducer (say approximately 130Ω). Before proceeding to Steps 3 and 4, the continuity should be checked between conductors and earthing screen of the electrical cable. If a continuity exists, a damaged cable is confirmed.

STEP 3

If the resistance across the two conductors is much higher than the values quoted in “STEP 1” (or is infinite), a severed cable must be suspected.

STEP 4

If the resistance across the two conductors is much lower than the values quoted in “STEP 1” (say 80Ω or less) it is likely that cable damage has occurred causing a short in the circuit.

STEP 5

If the resistance is within the values quoted in “STEP 1” (i.e. 120Ω to 180Ω), AND no continuity exists between conductor and earth screen and on checking the reading from the transducer, it proves to be still unstable or wildly fluctuating, it must be assumed that the integrity of the circuit is good. A faulty transducer could be suspected if neighbouring construction activities do not account for the anomaly. itmsoil Instruments Ltd. should be consulted. If the point at which the cable is damaged is found, the cable can then be spliced in accordance with recommended procedures.