The Underwater Sound Reference Division (USRD) of the Naval Undersea Warfare Center Division Newport operates and maintains a facility dedicated to performing low frequency calibrations of hydrophones and reciprocal transducers. The facility includes three closed, insulated pressure vessels, designated as Systems J, K, and L, and their associated acoustic measurement and environmental control systems. Each of these systems share the following characteristics:

• Receive sensitivity is measured via the comparison method (no transmission measurements are provided for devices under test).
• Measurements are conducted with continuous wave (CW) signals. Both standing wave and uni-directional waves are used in Systems J and L. System K operates in a standing wave mode only.
• Available Temperature Range: -3 to +40 degrees Celsius. Ground borne noise is minimized by isolating the test vessels with air bag suspensions.
• Calibrations are made by comparison with a reference hydrophone as verified by primary calibration in a reciprocity coupler.

Facility Specifications

Systems

System J

System J, a vertical test vessel, provides measurements in both a standing wave and in a uni-directional wave mode. The vessel contains two pressure compensated projectors (located at each end) and an array of six reference hydrophones placed along the vessel's length. These reference hydrophones provide the measurement system with field data (when a uni-directional wave is generated) and function as the reference hydrophone for the comparison calibration. Connections for devices under test are provided via underwater bulkhead connectors. One cable packing gland is also available; its use is dependent upon test pressure requirements and the physical properties of the cable being packed. A personal computer (PC) based measurement system provides the test vessel with signal transmission, data acquisition (up to four channels simultaneously) and control functions. System J has also been specially instrumented to conduct material characterization (velocity reduction) measurements on acoustic decoupling materials.

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System K

System K, a vertical test vessel, provides measurements in a standing wave mode only. The vessel contains one pressure compensated projector located at the top of the test vessel and a single reference hydrophone rigged opposite the device under test. Both the reference hydrophone and the device under test are rigged near the bottom of the vessel for the comparison calibration measurement. Connections for devices under test are provided via underwater bulkhead connectors; a cable packing gland is also available. The measurement system features a Hewlett Packard Model 3562A Signal Analyzer for signal generation and data acquisition.

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System L

System L, a horizontal test vessel, also provides measurements in both a standing wave and in a uni directional wave mode. For this system, an array of seven pressure compensated projectors are used at each of the two ends of the test vessel. As in System J, an array of six reference hydrophones are positioned along the length of the test vessel to provide field data and reference hydrophone functions. Connections for devices under test are provided via underwater bulkhead connectors; a cable packing gland is also available. A PC based measurement system provides the test vessel with signal transmission, data acquisition (up to four channels simultaneously) and control functions.

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Contact

For questions or assistance in obtaining measurement services, contact the Low Frequency Facility head at: 401-832-3252 or nuwc_npt_usrd_low_freq@navy.mil.