Product Lines

Televac Vacuum
Instrumentation Overview

This six-page brochure offers an overview of the primary Televac product lines. The brochure includes product illustrations, capsulized descriptions, and technical information.

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Much Ado About Nothing, Or...
So You Want to Measure Vacuum

This 28-page booklet offers an entertaining, informative description of basic vacuum measuring principles. A line in the opening paragraph sets the tone: "A little nonsense now and then is relished by the wisest men."

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Fundamentals of Vacuum Measurement, Calibration and Certification

Editorial Reprint. This six-page, full-color editorial describes and illustrates various types of vacuum instruments & basic means of vacuum calibration against standards for certification. Published in Industrial Heating, October 1992 issue.

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Control of Vacuum Furnaces for Heat Treating of Aircraft Gas Turbine Components

Editorial Reprint. Six-page, full-color editorial describes and illustrates methods used to control vacuum furnaces for heat treating or aircraft gas turbine components. Originally published in Industrial Heating; October 1994 issue.

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ARTICLES: Abstracts of scientific papers concerning ultra-high vacuum measurement - available from Televac

Vacuum Measurements Using Modern Cold Cathode Technology

Emil Drubetsky and Richard Glazewski
Televac, A Division of the Fredericks Company, Huntingdon Valley, PA

 

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Cold cathode gauges for ultra-high vacuum measurements

B. R. F. Kendall: Elvac Laboratories, Penn Eagle Industrial Park, Bellefonte, Pennsylvania 16823
E. Drubetsky: Televac Division of The Fredericks Company, Huntingdon Valley, Pennsylvania 19006

Nine cold cathode gauges have been evaluated on ion-pumped ultra-high vacuum systems operating at pressures down to the 10-11 Torr range. The test gauges included magnetrons, inverted magnetrons, and double inverted magnetrons from four different manufacturers as well as experimental variable-geometry gauges built especially for this project. Spinning-rotor and extractor gauges were used for calibration. The investigation covered repeated calibration over the 10-10 to 10-4 Torr range, stability over periods of up to 35 000 h of low pressure operation, tests for discontinuities in the current-pressure characteristics, stray magnetic field measurements, susceptibility to external magnetic fields, outgassing effects, and starting behavior at very low pressures. Our conclusion is that modern cold-cathode gauges are capable of giving far more accurate results than were possible with earlier Penning-type designs. Because of their extremely low outgassing rates, and their relative freedom from X-ray and electron stimulated desorption errors, they may in practice give results at low pressures which are more accurate than those obtained with typical hot-cathode gauges.

Starting Delays in Cold-Cathode Gauges at Low Pressures

B. R. F. Kendall: Elvac Laboratories, 435 Park Lane, State College, Pennsylvania 16803
E. Drubetsky: Televac Division of The Fredericks Company, 2400 Philmont Avenue, Huntingdon Valley, Pennsylvania 19006

A cold-cathode gauge does not immediately start when power is applied. Starting is generally assumed to be triggered by a cosmic ray or other energetic particle. The starting behaviors of two magnetron, two inverted magnetron, and five double inverted magnetron gauges were studied at pressures ranging from 2 x 10-7 down to 10-10 Torr. The effects of various starting devices (beta, alpha, field-electron, and photon emitters) were also evaluated. The median starting time for a given gauge was found to be approximately inversely proportional to pressure and consisted of two distinct components: a dormant interval and a growth period. The dormant interval is inherently nonreproducible, being governed by the statistical laws of random events. It can only be quantified by taking the median of a large number of measurements. It is normally by for the larger component and can amount to hours or days at 10-10 Torr. The growth period, on the other hand, is highly reproducible. It typically has a value of about 1 min at 10-10 Torr. For most of the growth period the discharge current is below the limit of detection, making it necessary to use special experimental techniques to determine the true growth period. A double inverted magnetron with radioactive triggering to reduce the dormant interval to less than a second at 10-10 Torr is described. Sources of error in starting-time measurements are discussed.

Stable Cancellation of X-Ray Errors in Bayard-Alpert Gauges

B. R. F. Kendall: Elvac Laboratories, 100 Rolling Ridge Drive, Penn Eagle Industrial Park, Bellefonte, Pennsylvania 16823
E. Drubetsky: Televac Division of The Fredericks Company, 2400 Philmont Avenue, Huntingdon Valley, Pennsylvania 19006

X-ray induced emission of electrons from the ion collectors of Bayard-Alpert gauges has long been recognized as a cause of falsely high readings at low pressures. Less well known is the existence of a reverse X-ray effect leading to a superimposed, but usually smaller, error signal in the opposite direction. First explained by Redhead and others in the 1960s as being caused by photoemission from the gauge envelope, this phenomenon was immediately recognized as potentially useful in cancelling the forward X-ray effect. Although promising experimental results were obtained with special gauge tubes, these early researchers concluded that the cancellation process was too unstable to be of any practical use. We report the results of an attempt to stabilize the cancellation process by the use of identical materials at the two photoemission sites. Experimental Bayard-Alpert gauge tubes were built with gold coatings on the interiors of the gauge envelopes and on the surfaces of the ion collectors. The envelope coatings were operated at approximately 15-25 volts below the potential of the ion collector. Stable reduction of the X-ray errors by a factor of more than 20 has been demonstrated. Short-term improvements by a factor of 100 have been achieved. Useful improvements have also been observed in sensitivity and in stability at high pressures. Results of long-term stability tests at pressures in the 10-10 Torr range are described.

For a copy of these papers, contact Televac.

Literature Request Form

If you would like more information sent to you, select any of the following articles or literature...

Literature

Televac Vacuum Instrumentation Overview

Fundamentals of Vacuum Measurement, Calibration and Certification

Much Ado About Nothing ...

Control of Vacuum Furnaces for Heat Treating of Aircraft Gas Turbine Components

Articles

Cold cathode gauges for ultra-high vacuum measurements

Starting delays in cold-cathode gauges at low pressures

Stable Cancellation of X-Ray Errors in Bayard-Alpert Gauges


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