AVS 50th International Symposium
    Vacuum Technology Thursday Sessions
       Session VT+MS-ThM

Paper VT+MS-ThM8
A New Look at the Modulated Bayard-Alpert Gauge

Thursday, November 6, 2003, 10:40 am, Room 323

Session: Reproducibility, Precision, and Accuracy of Vacuum and Process Measurements
Presenter: B.R.F. Kendall, Elvac Laboratories
Authors: B.R.F. Kendall, Elvac Laboratories
E. Drubetsky, Televac Division of The Fredericks Company
Correspondent: Click to Email
There is an increasing need for accurate vacuum measurements below 10@super-9@ Torr. Ordinary Bayard-Alpert gauges may have large and unpredictable errors at these pressures because of x-ray and other unwanted effects. Several special gauges have been developed to overcome these problems. One of the most cost-effective is the Modulated Bayard-Alpert Gauge (MBAG), first described by P.A. Redhead in 1960 and subsequently investigated in detail in many other laboratories. These gauges were widely used in Europe for several decades. We have evaluated several different MBAGs, ranging from first-generation glass-envelope types to a new miniature metal-envelope version. Performance data are given for operation in various modulation modes. An advantage of these gauge tubes is that, if necessary, they can be used as conventional BA gauge tubes with existing controllers. Some versions can be electronically adjusted for uniform sensitivity. The design of demodulation circuitry is discussed. X-ray errors causing gauges to over-read by several hundred percent at 10@super-10@ Torr can be essentially eliminated by using the modulation principle.