AVS 51st International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP14
The Effect of Dissolved Nitrogen Gas on the Density of Octoil-S --Working Fluid of the NIST 140 Pa Oil Ultrasonic Interferometer Manometer (UIM) Pressure Standard

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: J. Hendricks, National Institute of Standards and Technology
Authors: J. Hendricks, National Institute of Standards and Technology
A.P. Miiller, National Institute of Standards and Technology
Correspondent: Click to Email
The NIST Low Pressure Manometry Laboratory provides primary national pressure standards ranging from 0.01 Pa to 360 kPa. The topic of this presentation is the study of the density of octoil-s, the working fluid the NIST 140 Pa oil UIM which is the current NIST standard covering the pressure range from 100 Pa down to 0.01 Pa. The oil manometer was developed to avoid the ~ 0.2 Pa room temperature mercury vapor pressure that limits the lowest absolute pressure that can be measured with the NIST 360 kPa, and 160 kPa mercury UIMs. The NIST 140 Pa UIM is used to calibrate customer pressure transducers such as Capacitance Diaphragm Gauges (CDGs) of the appropriate Full Scale (FS) range, 0.1 torr, 1 torr, and the bottom ranges (0.01 FS and 0.1 FS) of 10 torr CDGs. The relative change in density of octoil-s as a function of nitrogen gas pressure was determined using a vibrating tube densimeter with a manufacturer's stated uncertainty of 5x10@super -6@ g/cm@super 3@ and a repeatability of 1x10@super-6@ g/cm@super 3@. Results will be presented showing that the effect of dissolved gas on the density of octoil-s does not contribute significantly to the uncertainty of the 140 Pa oil UIM. In addition, the results show that the performance of a planned 1,400 Pa oil UIM will not be adversely impacted by this effect. Finally, planned integration of the densimeter to the NIST oil UIM will allow periodic checks of the density of the manometer fluid should contamination be suspected.}