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cNODE transponders built-in tilt sensors support LBL operations

18. December 2013

All cNODE® transponders have a built-in tilt sensor, which is particularly useful in LBL operations. Here we have an example from an offshore field where mattresses are being installed in water depth of 330m. The ROV is using a cPAP® subsea transceiver and a Long Base Line array of 7 cNODE® transponders for high accuracy navigation.

At 12:12 hours LBL location number 6 gives high residuals. The range measurements from location 6 are automatically excluded by APOS and do not affect the positioning, but the residual still prequire some investigation.

Checking the built-in tilt sensor in the cNODE® transponder using telemetry, the sensor indicates the transponder stand has been knocked over during installation of one of the mattresses.

The ROV flies over to confirm and shows that the cNODE® transponder stand has been swept approx. 20m away from its initial seabed location.

The cNODE® transponder stand is placed in the upright position by the ROV.

The cNODE® transponder has to be calibrated into the array in its new position. This starts at 12:34 hours.

The calibrated position of location 6 is calculated at 12:40 hours, the whole calibration process has taken 6 minutes in total, and the LBL array is operational again with all it’s cNODE® transponders.

LBL positioning of the ROV can start again with location 6 in its new position.

Long Base Line calibration is fast with Cymbal acoustic protocol and cNODE® transponders

Timeline:

12:12

APOS shows large residuals on range measurements from the transponder in location 6.

12:13

Readings from the built-in tilt sensor in the transponder indicate the stand has fallen over.

12:19

The ROV confirms visually that the transponder stand has fallen over.

12:24

The transponder stand is placed upright again.

12:34

New baseline measurements to/from the transponder in location 6 starts.

12:40

The transponder is calibrated into the array again, the LBL array is operational and LBL positioning of the ROV commences.

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