Field Service Bulletin 26: SBE 49 FastCAT CTD

Publication Date: 
Friday, July 19, 2013
AttachmentSize
FSB26.pdf1.1 MB

Equipment Affected

This field service bulletin applies to all SBE 49s.

 

Description of Problem

Noise

A field report and subsequent testing at Sea-Bird revealed a noise signal in the temperature channel of approximately 2.5 mK peak-to-peak, at a frequency of 3 to 4 Hz. Parameters that are calculated using CTD temperature are affected similarly in magnitude and frequency (for example, salinity noise of approximately 0.003 psu peak-to-peak). The character of the noise is such that averaging of the SBE 49 data substantially reduces the effect of the noise. The SBE 49 samples at 16 Hz, and can be set up to average up to 255 samples (transmitting only the averaged data). The table and figure illustrate noise reduction through averaging data scans in the SBE 49.

For customers who are averaging 8 or more scans per sample in the SBE 49 and transmitting the averaged data, the noise is small compared to the instrument accuracy, and will have negligible impact on the output.

Sample Rate
(Hz)
Noise Amplitude
(mK, peak-to-peak)
Scans Averaged
16 2.5 (sampling rate)
8 2 2
4 1.25 4
2 < 0.5 7
1 < 0.2 16

 

Temperature Sensor Modification for Serial Numbers 0276 - 0320, corresponding to SBE 49s shipped August 2012 - May 2013
(serial numbers approximate; see photo to compare to your SBE 49)

In August 2012 Sea-Bird began using a thinner temperature probe than the previous design (see photo). The thin probe uses the same thermistor resistor component as the thick probe, but the sheath design was modified due to a material change. The change was intended as temporary, until we could reproduce the original sheath with a new material. Although there have not been any reported failures, Sea-Bird returned to the original thick probe design in June 2013.

 

Solutions

Noise

An electro-magnetic (EM) modification to the SBE 49 substantially eliminates the noise. Sea-Bird has implemented this modification in all SBE 49s built after May 2013 (approximately serial numbers 0321 and later).

Temperature Sensor Modification for Serial Numbers 0276 - 0320, corresponding to SBE 49s shipped August 2012 - May 2013
(serial numbers approximate; see photo to compare to your SBE 49)

Sea-Bird returned to the thick temperature probe design in all SBE 49s built after May 2013.

Warranty Policy for all SBE 49s built before May 2013

There is no need to return the SBE 49 immediately for modification, unless you are using it without averaging or with minimal averaging and the noise affects your data quality.

Sea-Bird will make the modifications described below when you return the SBE 49 for servicing (repair and/or calibration):

Temperature Probe Design Problems with Data?
(data does not meet customer needs
because of noise)
Customer returning SBE 49 for
Service that requires Disassembly?
(for example, repair or replacement of circuit boards)
Sea-Bird Response
Thick no no Perform requested service (standard charge)
no yes Perform EM modification (no charge)
in addition to requested service (standard charge)
yes no Perform EM modification (no charge)
yes yes Perform EM modification (no charge)
in addition to requested service (standard charge)
Thin no or yes no or yes Perform EM modification and change to thick temperature probe (no charge),
in addition to requested service (standard charge)
Applies To