The National Institute of Standards and Technology has completed and placed into calibration service a new Ultrasonic Interferometer Manometer that uses a low-vapor-pressure oil for the manometer fluid. This manometer operates up to 140 Pa with an expanded (k=2) uncertainty of U(P)=[(3x10~(-3) Pa)~(2)+(3.7x10~(-5) P)~(2)]~(1/2), where P is the pressure in Pa. Its completion has greatly simplified the calibration of low-pressure instruments and significantly improved the accuracy of the results for pressures below about 50 Pa.
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