We have been working to understand the details of a problem with the Druck pressure sensors used in SBE 41 and SBE 41CP CTDs on Argo floats. The problem is called Druck micro-leaks because, in 3 cases over the last two years where sensors were recovered, it was determined that oil was leaking out of a sealed inner sensor chamber through micro-cracks in glass-to-metal seals at the back of the sensor. The oil leak rate is very slow, just a few micro-litres per month. As oil leaks, a flexible titanium diaphragm, that transmits ocean pressure to the oil chamber, deflects into the sensor chamber to make up for the oil loss, and as a consequence, the sensor develops a progressive negative offset in measured pressure. This becomes evident in Argo data as a negative surface pressure. With enough oil loss the diaphragm deflects inward far enough to contact and short out the pressure sensing element. There is evidence that the diaphragm bottoms out and does not result in a further leak of oil or ocean water through the sensor.
We welcome your questions and will do our best to answer them completely.
Warranty and Instructions for Returning CTDs
Sea-Bird's warranty policy is dependent on whether the float has been deployed or not:
Case 1: Floats that are not
yet deployed --
Please return these CTDs/floats (return instructions)
Case 2: Floats that are
Sea-Bird will provide information (in the near future) on how to recognize the micro-leak problem through an analysis of the float's pressure data. If Sea-Bird agrees that the pressure sensor data indicates a micro-leak problem, we will issue a certificate to the user for a free CTD for use on a subsequent float.
Case 3: Floats that are not
yet deployed, but which must be deployed --
If you must deploy these floats because of substantial commitments, Sea-Bird will treat these in the same manner as floats that have been deployed (Case 2).
Sea-Bird Home Phone: (+1) 425-643-9866 Skype: sea-bird-electronics E-mail: email@example.com