Field Service Bulletin 22: SBE 3 Frequency Shift with SBE 25 CTD and Cold Temperature Applications
This field service bulletin applies to SBE 3s that meet all of the following criteria:
- SBE 3plus, 3F, or 3S with serial numbers 5179 and higher.
- Integrated with an SBE 25 CTD or a non-Sea-Bird system that provides less than 11.5 V of power to the SBE 3
- Used in very cold water (approximately 2 °C or less)
Note: The Field Service Bulletin does not apply to an SBE 3 on an SBE 9plus CTD; the 9plus provides a much higher voltage to the SBE 3, eliminating any possibility of the frequency shift described below.
Description of Problem
For the specified SBE 3s, customers may see a frequency shift in the SBE 3 output, resulting in decreasing the period of the output frequency by approximately 6.4 µS (corresponding to approximately ±0.1 °C) when at 2 °C or below and at lower than typical supply voltage. The frequency shift appears as a step change in the data, and remains as an offset in the data until the temperature rises above approximately 2 °C or the supply voltage is increased.
- The SBE 25 provides 11.5 V ± 0.125 V to the SBE 3. The frequency shift is likely to occur only on the low end of the specified voltage range.
We are unaware of any customers with bad data as a result of this problem.
If your data demonstrates the shift described above, contact Sea-Bird and send us the data for evaluation. If we agree that the temperature data exhibits the frequency shift problem, we will replace the SBE 3.