Abstract: Apparatus for measuring the power of radiation that includes float means (16) and force balancing means (48, 50, 60, 80). The float means includes a target (46) for the radiation and is constructed such that the net gravitational force, including buoyancy force, if any, acting on the float means tends to accelerate the float means in a first direction. The force balancing means includes drive means (80) for providing a drive signal and means (50) responsive to the drive signal for exerting a balancing force on the float means in a second direction opposite the first direction, such that the magnitude of the balancing force corresponds to a characteristic of the drive signal.

Abstract: An apparatus for calibrating a force measuring instrument of the type that includes a force sensitive element submerged in a liquid. The apparatus comprises a magnetic object having a known weight when submerged in the liquid, and an electromagnet. The electromagnet includes a core having a first end that extends beneath the surface of the liquid to a position near the upper surface of the force sensitive element. The electromagnet further includes a coil surrounding a portion of the core, means for energizing and deenergizing the coil, and a thermal insulator surrounding the first end of the core to prevent the core from contacting the liquid and to limit heat flow from the core into the liquid. When the coil is energized, the magnetic object is picked up from the force sensitive element and adheres to the insulator. When the electromagnet is deenergized, the magnetic object falls back onto the force sensitive element for calibration of the instrument.

Abstract: A precision acoustic source that is capable of producing acoustic radiation having peak and average power levels that are independently and simultaneously adjustable. The apparatus comprises an acoustic transducer and drive means for producing a drive signal comprising a series of drive pulses to the transducer, such that the transducer produces acoustic radiation having selected peak and average power levels. The drive means comprises means for establishing a series of fixed-length clock cycles, means for generating a series of trigger signals, pulse generating means responsive to each trigger signal to produce a selected number of standard pulses, an amplifier for generating a drive pulse in response to each standard pulse. The amplifier adjusts the amplitude of each drive pulse such that the peak power of the acoustic radiation is equal to the selected peak power level. Each trigger signal occurs either R or S clock cycles after the preceding trigger signal, R and S being positive integers.