Gauge Head Research Articles

Inverted magnetron manometer with enhanced operating time

If a cold-cathode ionization gauge is operated in a gas atmosphere with a high content of hydrocarbons at high pressures, the pressure reading of the gauge is disturbed by the contamination after a certain time of operation. Since in the most cases it is not possible to eliminate these disturbing residual gas components, one has to demand that the measuring process may not be substantially influenced by these gas components. To enhance the time of reliable pressure reading of a cold-cathode gauge we have equipped the entrance of an inverted magnetron gauge head with an ion baffle. By this measure the time of a reliable operation of the gauge is increased at least by a factor 3. The construction of this ion baffle is rather simple. It does not require any additional voltage supply or additional magnets. An additional feedthrough is only necessary for the measurement of the discharge current of the measuring system. The gauge has a range of pressure measurement from 10 −9 to 3×10 −3 mbar.

On the use of a capacitive diaphragm gauge for dust detection in next-step fusion devices

The technology underlying a ceramic capacitive diaphragm gauge (CDG) manometer has been investigated for use as a microbalance for measurement of dust accumulation in next-step fusion devices such as ITER. Initial trials have confirmed in principle the use of CDG devices as dust microbalances and both the gauge head and electronics have been adapted to address the environmental constraints. Remote electronics, capable of controlling the gauge at a distance of 30m, have been developed and a prototype device has been tested in the laboratory, where a sensitivity of 500μg∕cm2 and dynamic range of at least 103 were demonstrated. The work shows that this approach is a promising contender to measure dust accumulation in next-step fusion devices.

Development of a rapid profilometer with an application to roundness gauging

Abstract This paper presents the development of a real-time, contact-based, high frequency, response profilometer employed as a roundness gauge for measuring circular form error for 100% part inspection on the shop floor with an accuracy of better than 0.5 μm with measurement times of less than 1 s. The gauge head is a closed-loop controlled mechanism comprising a contact force probe that is rigidly attached to a high bandwidth linear translator. The gauge head assembly is, in turn, attached to a precision spindle. The objective of the complete tool is to contact the sidewall of the circular feature, translate the probe tip to produce a defined contact force with the workpiece and rotate the gauge head assembly. During rotation of the spindle, this contact force is maintained at a nominally constant value by dynamically translating the force probe along a radial direction to follow surface deviations. The gauge head assembly (including force probe and servo drive) has a fundamental mode natural frequency of 330 Hz while scanning the workpiece with a constant contact force typically less than 100 mN. Form error (deviation from a nominal circle) is measured using a capacitance-based displacement sensor measuring the relative radial displacement of the probe with the spindle rotating at a constant rotation speed. This paper discusses the design and characterization of this metrology tool.

放射線等による圧力測定異常とその対策

In the SPring-8 Storage Ring, the pressure measured by Bayard-Alpert gauge near photon-absorber were not observed aging effects by a beam self-cleaning. As the result of investigations of this phenomenon, three causes of misreading of pressure measurement were found; (1) irradiation of the scattered X-ray to gauge head, (2) a large amount of electronic inflow to gauge head, (3) irradiation of the scattered X-ray to gauge cable. We took measures to the misreading, for example shielding of gauge heads and cables etc, and came to be able to measure pressure within tens of percent errors.

Hot-cathode-ionization-gauge system with a self-compensating circuit for errors caused by an external-electron source

A hot-cathode-ionization-gauge system, consisting of a gauge head with a correcting electrode, an automated-pressure-compensating circuit, and a shield tube, succeeded in overcoming two kinds of erroneous pressure indications with hot-cathode-ionization gauges. Several tens of hot-cathode-ionization gauges in the SPring-8 storage ring have indicated abnormally low pressures (of the order from 10−8 to 10−9 Pa) at stored-electron-beam conditions due to an influx of photoelectrons. Some of these gauges, located near photon absorbers, have indicated negative pressures (from −2×10−9 to −2×10−7 Pa). To investigate these pressure-measurement errors, simulated experiments to reproduce the phenomena were carried out using an external-electron source which was located near a hot-cathode-ionization-gauge head. The kinetic energy of incident electrons to the gauge head from the external-electron source was varied from 10 to 90 eV. The maximum total-electron-beam current from the external-electron source at the position of the gauge head was about 0.12 mA (90 eV), which was 3% of the normal emission current from the gauge filament. In the pressure range of 10−7 Pa, the pressure-measurement errors which occur in the ring were reproduced. During the experiment, the variation of the indicated emission current was less than 1% of the normal emission current. With no emission from the gauge filament, negative currents were detected at the grid and the collector of the gauge from the external-electron source at the same pressures as in the simulated experiment. It was found that detected negative current at the grid of the gauge was 50%–60% of the total-electron-beam current from the external-electron source and it was confirmed that the detected negative current at the collector depends on the kinetic energy of the incident electrons. From these results and calculations, it was also found that the variation of the emission of the gauge filament did not cause the negative-pressure indications at all. Furthermore, it was also confirmed that the hot-cathode-ionization gauge indicated abnormally low pressures or negative pressures when the net current detected at the collector in operation of the gauge was extremely small or negative, respectively, due to the influx of many electrons from the external environment. These experiments were done to simulate operation conditions at the SPring-8 storage ring. In the simulated experiments for abnormally low-pressure indications, pressure measurements using a hot-cathode-ionization-gauge head with a correcting electrode and an automated-pressure-compensating circuit were carried out in the pressure range from 10−6 to 10−8 Pa. It was found that the compensated pressure indicated the actual pressure within an error range of ±15% for incident electrons with 20 eV, although the indicated pressure of the ionization-gauge controller was in a different order than that of the actual pressure and the error current was less than the order of 10−10 A. In the simulated experiment for negative-pressure indications, it was found that the shield tube could reduce incident electrons from the external-electron source by a factor of about 1/10.

An odd kind of fame: Stories of Phineas Gage

Over 150 years ago, in an industrial accident, a tamping iron was blown through Phineas Gage's head. The resulting personality change - he was “no longer Gage” - has featured widely in neuroscience and psychology courses. Take a moment to marvel at the unlikely occurrence: an iron bar, thicker than a broomhandle, crashes through a man's head. He “is able to walk off, talking with composure and equanimity of the hole in his head. …

Formation of negative electromotive force and degradation of insulation resistance in ionization vacuum gauges

Authors have observed an unusual phenomenon that the collector current in an Extractor vacuum gauge, which several times experienced a bakeout of 570 K, about 70 h, becomes negative at pressures in or near the XHV region. To investigate the causes, the temperature dependence of the collector current, the electromotive force (e.m.f.), and the insulation resistance of the collector electrode for both an “unusual” and a new gauge were measured. As a result, their dependence for the unusual gauge showed strikingly different behaviors from those for the new gauge. These results suggest that some new structure is formed in the gauge head by several bakeouts. Also it was found that the new gauge shows a positive larger e.m.f., but the current due to this e.m.f. was very small because the collector electrode has a very high insulation resistance.

Frontal lobe function: Mr. Phineas Gage's famous injury.

T next article in our series is a case report written in 1848 by John M. Harlow, M.D., describing his care of Mr. Phineas Gage, who suffered an extreme injury to the frontal cortex. Mr. Gage was employed as a railroad worker in Vermont and fell victim to a freak accident that involved a long metal rod called a tamping iron. This rod was used to pack sand over an explosive charge, which was used to excavate rock for the building of railroad lines. In this instance the charge exploded unexpectedly and propelled the 3-foot-long rod through Mr. Gage’s head. The 13-pound rod entered the left cheek and exited the midline of the skull anterior to the bregma, resulting in severe injury to his left and, in all probability, his right prefrontal cortex. The Gage case, one of the most famous and influential in neuropsychiatry, played a crucial role in the discovery of behavioral syndromes resulting from frontal lobe dysfunction. Readers interested in detailed accounts of the case and its historical context can find excellent reviews by MacMillan and Barker. The case report was initially met with disbelief because it was thought to be impossible for a human to survive a brain injury of such magnitude. Beyond the astonishing fact of Mr. Gage’s survival was the description of his ability to walk immediately after the event, communicate sensibly, and remain lucid though most of the period following the injury. This fact attracted the attention of P. T. Barnum, who employed Mr. Gage for a short period following his recovery. Dr. Henry J. Bigelow, a prominent professor of surgery at Harvard Medical School, examined Mr. Gage after Harlow’s report and failed to note the changes in Gage’s behavior. He proclaimed that Gage had no demonstrable sequelae of the injury. Dr. Bigelow and others used the Gage case as a persuasive argument against the field of phrenology, which was the only prominent discipline at the time that considered the possibility of localization of brain function. Yet, as the reader will note, there are several suggestions in the original report that Mr. Gage’s behavior had changed. Dr. Harlow promised to report the mental manifestations of the injury in a subsequent communication. He did not produce this report until 20 years later, when he described a pervasive change in personality and character in the Journal of the Massachusetts Medical Society, a periodical with very limited circulation. In this report, Harlow described the following:

A case study of the effect of lubrication and profile grinding on low rail roll-over derailments at CSX transportation

Kingsport and Blue Ridge are two subdivisions of CSX Transportation's Corbin Division. Annually they carry 42 million gross tons (MGT) of predominantly 100 ton coal car traffic through Kentucky, Tennessee, and North Carolina. Because of the mountainous terrain, the track has several sharp curves (up to 14°) and steep grades (up to 1.2%). Between the period of January 1990 through October 1991, eight derailments occurred. Some of the derailments were called low rail roll-over derailments and the others, although not listed as low rail rollover derailments, had several common features. Under normal operating conditions the track structure would have been considered good. However, because of the rugged conditions on these two subdivisions, the track structure needed strengthening and upgrading. Factors contributing to low rail roll-over include heavy axle loads, under-balanced train speeds, inadequate lubrication, wide track gauge and poor rail head profiles. During the period of the derailments, maintaining track gauge, line and level was a continuous operation. In the sharp curves, damage occurred rapidly to newly replaced timber ties and premium head hardened rail. The average life of the low rail in a 14° curve was 18 months (60 MGT). These conditions were costly and required a solution. Research and tests carried out by National Research Council of Canada, CSX Transportation and Loram Maintenance of Way, led to the development of a comprehensive lubrication and grinding program. The lubrication emphasized friction control between the low rail-wheel interface. The grinding method was changed from corrective to preventive. NRC/ LORAM asymmetric profile geometry of low and high rails was scrupulously maintained. Since the implementation of these two programs, there has not been a low rail roll-over derailment or a derailment with any feature associated with low rail roll-over derailment.

An improved throughput method for the measurement of outgassing rates of materials

A modified throughput method using a system with an extremely high vacuum (XHV) pump was developed to determine the outgassing rate of a vacuum chamber type sample accurately eliminating the contribution of outgassing from the vacuum gauge. The up-stream and down-stream sides of an orifice were connected with two sets of bridges, each of which consisted of one gauge head on a T-tube and two valves to terminate the tube. Hence the combination of the space being measured and the gauge was selected by the valve operation. A mass spectrometer was also set to the similar bridge to analyse the outgassing species. The outgassing rates of the total and the gauge were measured using the different valve combinations and the true outgassing rate of the sample was that of their difference. The outgassing rate of an electrolytically polished stainless steel chamber with TiN inner coating was determined at various temperatures after baking at 150 °C. Only hydrogen was then released at a specific rate at room temperature, of 7 × 10 −11 Pa·m·s −1, which was sufficiently low for use of the wall material in XHV equipment.

Spinning rotor gauge for operation at free spatial orientation

A spinning rotor gauge (SRG) head with reinforced magnetic suspension and its metrological properties are presented. The new gauge can be operated at any orientation of the gauge head. Usually the gauge head stays with its axis vertical on the thimble (sensor tubing) which is fixed to the horizontal. Industrial applications sometimes require the thimble to be orientated in a non-horizontal position. This necessarily requires the gauge head axis, that is always perpendicular with respect to the thimble, to be tilted against the vertical. When the gauge head axis is vertical the magnetic drag on the rotating sensor is a minimum, effecting a residual pressure indication of the order of 10 −4 Pa, air equivalent. Maximum drag occurs with the gauge head axis horizontal. This is about 0.3 Pa equivalent, with a long-term stability of better than 10 −3 Pa. The rotor deceleration-versus-pressure characteristics were investigated for various inclination angles of the gauge head at pressures from atmospheric down to 10 −4 Pa.

Vacuum

A highly versatile new ionization gauge, the IMG 300, has been introduced by Balzers High Vacuum Limited, Milton Keynes, to control and monitor vacuum installations and plasma and sputtering processes. In its basic configuration, the IMG 300 is a simple ionisation vacuum gauge which can be bench or rack mounted. When a high-pressure (HP) gauge head is fitted, the IMG 300 covers the l-10-6mbar range, while a Bayard- Alpert (BA) gauge head covers the measurement range from 10-2–10-9mbar. The high-pressure gauge head is immune from electric and magnetic interference often encountered in process plant.

The effect of rotor acceleration on the zero stability of spinning rotor gauges

The zero stability of spinning rotor gauges, in particular after the initial acceleration of the magnetically suspended ball-rotor, was investigated for different ball materials and frequencies of the inductive drive. With standard Cr-steel balls and 16 kHz drive the drift of zero-readings typical ranges up to ± 1×10 −7 mbar N 2 equivalent during the first 2 h subsequent to the initial speeding-up from 0 directly to 415 rps (no overshoot). This is traced back to temperature imbalances generated inside the gauge head by the motor currents, which lead to variation of the rotor dimensions and so to ball-speed changes during temperature equalization. The zero stability can be improved (about one order of magnitude) by using balls made of material with low thermal expansion (NiFe). A lower frequency (∼3 kHz) drive was found to reduce the settling time of zero-readings appreciably.

中耳圧の体平衡におよぼす影響

The influence on human equilibrium of positive and negative middle ear pressure was studied with a strain gauge platform and head position sensor system. The data obtained were digitalized and analysed by a microcomputer, Deviation of head and body sway center followed by eye closure was adopted as the parameter for the analysis. Three groups of people were examined; 1) patients with unilateral otitis media with effusion (OME), 2) normal volunteers, 3) patients with middle ear ventilation tubes on one side. Patients in group 1 were examined before and after the treatment of OME. Those in groups 2 and 3 were examined with positive or negative pressure applied on the ear randomly chosen (group 2), or on the ear with a ventilation tube inserted (group 3). The OME patients' head deviation to the affected side turned to the opposite side right after treatment. Head deviation similar to that of the untreated OME patients was observed when positive external earcanal pressure (group 2) or negative middle ear pressure was applied. The shift of the stapes' foot plate might be one of the causes of these head deviations. More studies are needed to clarify the mechanisms of disequilibrium produced by unusual middle ear pressure.

The spinning rotor gauge

The determination of pressure in a high vacuum from the gaseous drag of a freely rotating sphere was already proposed in 1946 by Beams and co-workers. On the basis of novel techniques, this method was developed from its original bulky and delicate experimental state to a practicable, compact instrument for widespread laboratory and industrial use. The present paper gives a detailed description of the gauge head functions, and of the method of evaluation of the rotor deceleration rate. The predictability of the gaseous drag is discussed in view of absolute pressure gauging. The feasibility of extending the measurement range up to atmospheric pressure is demonstrated on the basis of experimental results.

Modulating ion current pressure gauge

A remote pressure measurement system suitable for ultra-high vacuum in a very severe noise environment, such as found in high energy accelerators, is reported. The pressure in a beam pipe of the 12 GeV proton synchrotron at the National Laboratory for High Energy Physics has been measured with high accuracy by a newly developed hot-cathode extractor type ionization gauge, here called the modulating ion current gauge. The output signal from the gauge head was sent to the synchrotron subcontrol room by a 120 m long cable and the measurement was carried out with full beam in the synchrotron. The miniaturized gauge head has a hemispherical mesh anode and a cylindrical electrode between the ionization region and the ion-collector to modulate the ion current. The modulated signal is sent to an amplifier via a double shielded coaxial cable and after amplification is detected with a phase sensitive detector. This new gauge can reject externally induced noise. The effects both of ions desorbed by electron-impact from the anode and of X-ray photocurrents from the ion-collector can also be avoided.

Acoustic method and apparatus for measuring micron and submicron distances

A gauge for measuring variations in distance of a surface relative to a reference by means of phase shifts in a zone of high acoustic impedance. A gauge head is provided with a first orifice for emitting acoustic waves, driven by a reference signal, toward a surface positioned very close to the gauge head, forming a high impedance zone. A second orifice in the gauge head picks up acoustic waves subjected to the zone and these waves are converted to electrical signals for comparison to the reference signal in a phase detector. The phase error between the two signals is indicative of surface distance variations.

Calibration of Shock and Vibration Measuring Transducers

Abstract : This book is an authoritative reference on the calibration procedures used in both primary and secondary calibration laboratories. Contains well- established basic calibration methods, describes transducer, force gage, and impedance head characteristics to the limited extent necessary to aid in performing accurate calibrations. The use and interpretation of results and a detailed description of errors are given. Primary and secondary standards, reciprocity and comparison methods are discussed. Describes the use of calibration shakers and shock motion calibrations. All necessary basic equations are developed.

Methods of pumping speed and gas release measurement in ionization gauge heads—A review

The problems associated with the change of both the equilibrium and composition of the residual gas within ionization gauge heads during measurements are presented. The phenomena which contribute to the specific shape of the plot (log P,t) are discussed in some detail as a basis for understanding the behavior of gauge heads as sinks and/or sources of gas. A critical analysis of the physical principles underlying the methods for the determination of a gas removed/or re-emitted is given. Understanding of the processes discussed will permit the selection of the most adequate method for the measurement of the pumping and gas release in an ionization gauge head during its operation. By using suitable experimental methods, accurate determination of these characteristics is possible. The results obtained can be used to correct the pressure readings taken with gauge heads in which ionized gas is used as a means of determining gas density.

変調イオン電流ゲージ

The pressure in a beam pipe of the 12 GeV proton synchrotron of National Laboratory for High Energy Physics has been measured with a high accuracy by the new developed modulating ion current gauge (MIC-G). The output signal of the gauge head was sent to the sub-control room of the synchrotron by a 120 m long cable and the measurement was carried out when a proton beam was accelerated in the synchrotron. The gauge head has a modulator electrode between an ionization region and an ion collector to modulate the ion current. The modulated signal is sent to an amplifier with a double shielded cable and then it is amplified and detected with a phase sensitive detector (PSD). This method can reduce externally induced noise and the influences of desorbed ions by a electron impact from an anode electrode and of X-ray photoelectric currents from an ion collector can be also avoided.