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Hydrophone Handbook

               Best Practices

 9.3 Measurements:
 1. Establish a routine monitoring scheme to check the health

      of your measurement instruments. Before starting
      measurements, it is best to use a stable reference
      transducer (or “gold” standard transducer) to regularly test
      your acoustic measurement system. SPC tracking will help
      establish appropriate control limits to identify anomalies
      early.
 2. Control and monitor the water temperature. Hydrophone
      calibrations by Onda are done at 23.5 °C.
 3. Use a dissolved oxygen meter to regularly monitor the
      dissolved oxygen level in the water.
 4. Ensure that the impedance set on the oscilloscope matches
      the output impedance of the hydrophone (e.g., 50 Ω with
      preamplifier and 1 MΩ without preamplifier).

 9.4 Calibrations:
 1. Maintain Hydrophone calibrations, typically recommended

      once per year. To start, complete the Hydrophone
      Calibration Questionnaire to specify the calibration option(s)
      and the hydrophone configuration.
 2. Establish a calibration strategy. Some users have a second
      hydrophone set available to limit any measurement
      downtime when the primary hydrophone is sent for
      calibrations. Other users have established a scheme where
      dedicated “workhorse” hydrophones are traceable to
      reference hydrophones.

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