Frequently Asked Questions

Overview:   Connect a Model 831 to an underwater hydrophone. 

Features :  Model 831 Measures underwater noise.

The 831 can connect to a piezoelectric hydrophone -

1. Replace the microphone with an ADP005 ‘dummy mic’ adapter
2. Connect the hydrophone to the BNC connector end of the ADP005
3. Using the adapter, place the hydrophone in a pistonphone adapter to calibrate
4. On the Model 831 select TOOLS and create a calibrator entry for the pistonphone.  Set the calibrator level to the appropriate level (see below) and the frequency to 250 Hz.  The level may be different for differing models of pistonphones.  Consult the pistonphone manufacturer’s documentation to determine the correct level.
5. Calibrate. Although reference pressure levels differ for measurements in air and water, this step will adjust the Model 831 for to account for this difference. 20 μPa is typically used as a reference for air, and 1 μPa for water. The difference is 20x in the linear domain, and 26 dB (26.02 dB to be exact) in the log domain. As an example, 1 Pascal pressure equates to 94 dB re. 20 μPa in air and 120 dB re. 1 μPa in water.

Note: When using the RA0043 hydrophone adaptor with a pistonphone, the volume is changed slightly and therefore a hydrophone calibration adapter correction factor should be applied. The calibration factor can be found on the RA0043 calibration chart or is etched on each adapter.

Note: the K-Factor can also be verified in the field by using the 1/2" sampling port on the side of the adapter.

Example: To calibrate using a standard 114 dB pistonphone such as GRAS 42AA, enter 144.5 dB:

use actual sensitivity from calibration sheet to change reference pressure from 20 μPa in air to 1 μPa for water K-Factor, correction for volume difference when using RA0045 Sensitivity to enter in 831 when calibrating TC4013 hydrophone