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Title: High vacuum measurements and calibrations, molecular flow fluid transient effects

High vacuum pressure measurements and calibrations below 1 × 10-8 Torr are problematic. Specifically, measurement accuracies change drastically for vacuum gauges when pressures are suddenly lowered in vacuum systems. How can gauges perform like this? A brief system description is first required to answer this question. Calibrations were performed using a vacuum calibration chamber with attached vacuum gauges. To control chamber pressures, vacuum pumps decreased the chamber pressure while nitrogen tanks increased the chamber pressure. By balancing these opposing pressures, equilibrium in the chamber was maintained at selected set point pressures to perform calibrations. When pressures were suddenly decreased during set point adjustments, a sudden rush of gas from the chamber also caused a surge of gas from the gauges to decrease the pressures in those gauges. Gauge pressures did not return to equilibrium as fast as chamber pressures due to the sparse distribution of gas molecules in the system. This disparity in the rate of pressure changes caused the pressures in different gauges to be different than expected. This discovery was experimentally proven to show that different gauge designs return to equilibrium at different rates, and that gauge accuracies vary for different gauge designs due to fluid transients inmore » molecular flow.« less
Authors:
 [1] ;  [2]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River Nuclear Solutions.
  2. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL).
Publication Date:
OSTI Identifier:
1223188
Report Number(s):
VAC-D--15-00161
Journal ID: ISSN 0042-207X; PII: S0042207X15001827
Grant/Contract Number:
AC09-08SR22470
Type:
Accepted Manuscript
Journal Name:
Vacuum
Additional Journal Information:
Journal Volume: 119; Journal Issue: C; Journal ID: ISSN 0042-207X
Publisher:
Elsevier
Research Org:
Savannah River Site (SRS), Aiken, SC (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY fluid transient; molecular flow; ion gauge; spinning rotor gauge; capacitance diaphragm gauge; cold cathode gauge; vacuum measurement; vacuum calibration; vacuum measurement errors