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7 – Operating Procedure

DPN 402197 © TSS (International) Ltd Page 27 of 30

Where vibration is fast and severe, the resultant induced signals could interfere with

the signal from the target cable.

Slow movements, such as those of the ROV manoeuvring, will have a negligible

effect since the resulting induced voltages will be at a frequency below the pass-band

of the 350 System.

Summary:

Follow the installation instructions throughout this Manual. Ensure the coil mounting

arrangements provide a rigid support that damps vibrations quickly.

Operate the ROV at a speed that avoids the onset of vibration.

Select a tone frequency that does not coincide with the frequency of vibration.

Power-carrying Cables

If you use the 350 System to survey power cables that carry high currents, the coils

might experience saturation. If this occurs, the System will be unable to calculate the

position of the target.

The most effective way to cure this problem is to remove power from the cable or to

operate the ROV at a greater distance from the target.

Impressed-current Cathodic Protection

When surveying near sub-sea pipes or metallic structures that use impressed-current

cathodic protection, the 350 System might suffer from noise pick-up. Provided the

tone frequency is different from that of the cathodic protection the System will be able

to discriminate between the two.

Use the display software to confirm whether such noise breakthrough is occurring.

Summary:

Perform regular checks on signal quality and on the signal-to-noise ratio by using the

SDC display software.

If cathodic protection currents present a problem, arrange to switch off the current

while you perform the target survey. The interference will disappear immediately

although the protection afforded by the current will remain for some time afterwards.

Operating over Ferrous Rock Dumps

Operating the 350 System over a ferrous rock deposit or dump might affect measure-

ments. This is because the ferrous content of the rock will introduce a random distor-

tion to the magnetic fields radiated by the tone-carrying cable.

This distortion varies with the nature of the rock and there is no way to predict the

magnitude of errors introduced.

Summary:

Where possible avoid conducting a survey in areas where the rock formations have a

significant ferrous content.

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