Abstract: An audiometric instrument that includes a dual pressure transducer configuration along a common air line with a first pressure transducer situated in a probe proximate to the ear of a user and a second pressure transducer situated proximate to a pressure control device. A restriction is preferably placed in the air line between the two pressure transducers to assist with obtaining a better comparison of the local pressure measurements from the different pressure transducers.

Abstract: A hands-free dual audiometric probe headset. In one embodiment, the headset includes a resilient headband attached to a first audiometric probe holder including a first audiometric probe attached thereto and a second audiometric probe holder including a second audiometric probe attached thereto, the headset system configured to reliably hold the audiometric probes in place in the ears of a test subject during binaural testing.

Abstract: An ear canal pressurization device optimized for aural acoustic immittance testing is disclosed. Changes in volume of a first flexible chamber, due to motor movement, produce changes in ear canal pressure based on Boyle's law. A vent may be opened to allow ear canal pressure to gently equalize to ambient air pressure or to generate ear canal pressure sweeps free of pressure baseline offset. The vent may be closed to set a static ear canal pressure or to generate ear canal pressure sweeps with an incidental baseline offset. The vent may be controlled to generate ear canal pressure sweeps with an intended baseline offset. The device produces ear canal pressure proportional to drive voltage, so any desired pressure versus time function can be generated by applying a coil driving voltage with the appropriate amplitude versus time function.

Abstract: An ear canal pressurization device optimized for aural acoustic immittance testing is disclosed. The preferred embodiment of the device is comprised of a rigid mounting framework which holds in position, axially aligned, a first flexible chamber assembly, a centrally disposed forcer assembly, and a second flexible chamber assembly. The forcer assembly comprises a ferromagnetic bobbin and coil that provides electromotive force for a moving magnet linear motor. The motor is comprised of a rigid chamber link, which passes through the hollow core of the bobbin, with a ferromagnetic keeper washer and axially aligned rare earth ring magnet at either end, with like magnetic poles facing each other. The motor is elastically suspended between the first and second flexible chambers.

Abstract: A system is described which makes it possible for an audiometer to measure, analyze, and respond to acoustic signals that are present near the opening to the ear canal during audiometric testing. The signals monitored are those produced by the audiometer itself and any ambient noise present in the test environment. The system is implemented by permanently mounting a measurement microphone in each earphone enclosure so that the microphone can monitor the acoustic signals being produced by the earphone. The acoustic signals and ambient noise levels are then sampled and the sampled acoustic data is analyzed to provide verification of test signal integrity and to stop testing when the ambient noise level exceeds an acceptable level.

Abstract: An improved tympanometric testing means is described for automatically testing the status of the middle ear. The testing unit provides a recording on a chart showing a change in the compliance of the middle ear during change of the air pressure in the external ear. The tympanometric test unit operates automatically as the clinician inserts the test probe into the patient's ear. The unit automatically determines that the probe is in an unblocked condition and that the test probe tone is at a proper intensity relative to the ear canal volume. When these conditions are met and the ear canal pressure at the probe reaches the predetermined test start pressure, the unit proceeds with the testing as the pressure in the ear canal moves between desired limits such as between the +200 and -200 mm H.sub.2 O and while the recorder makes a plot of the ear drum compliance.

Abstract: A rotary shredder for waste materials has a pair of counterrotating cutting shafts, each of which mounts a series of spaced-apart disc-type cutters. The cutters on one shaft extend into the spaces between cutters on the other shaft so that the cutters on the two shafts coact to shred material fed therebetween. The two shafts are driven by a reversible radial piston hydraulic motor through a gear train arranged to rotate one cutter shaft at twice the speed of the other. The hydraulic motor is driven by an electric motor-driven fixed or variable displacement pump. A flow-reversing valve in the hydraulic motor control circuit controls the direction of fluid flow through the hydraulic motor. The reversing valve is electrically actuated automatically by a fluid pressure-operated switch to reverse flow and the direction of rotation of the cutters to prevent jamming whenever fluid pressure in the motor circuit rises to an abnormally high level.

Abstract: A hydraulic power supply unit has a fluid reservoir and a motor-driven pump which delivers fluid under pressure to a hydraulic system through a check valve in a fluid supply line. A hydraulic pressure accumulator downstream of the check valve helps maintain the system under a predetermined pressure. An accumulator pressure release valve automatically relieves the accumulator and thus the connected system of hydraulic pressure when the pump is inactive. The valve has a valve body with a pilot port connected to the discharge side of the pump upstream of the check valve, an accumulator port in communication with the accumulator and a return port in communication with the reservoir. Internal passages within the valve body interconnect the pilot, accumulator and return ports. A movable valve member within the valve body moves to a closed position when the pump operates to block flow from the accumulator port to the return port, thereby pressurizing the accumulator and the system.